1966-67 Seasonal variation in phytoplankton from lake rotorua and other inland waters, New Zealand

New Zealand Journal of Marine and Freshwater Research

                       ISSN: 0028-8330 (Print) 1175-8805 (Online) Journal homepage: http://www.tandfonline.com/loi/tnzm20

                Seasonal variation in phytoplankton from lake
                rotorua and other inland waters, New Zealand,

                Vivienne Cassie

                To cite this article: Vivienne Cassie (1969) Seasonal variation in phytoplankton from lake
                rotorua and other inland waters, New Zealand, 1966–67, New Zealand Journal of Marine and
                Freshwater Research, 3:1, 98-123, DOI: 10.1080/00288330.1969.9515280

                To link to this article: http://dx.doi.org/10.1080/00288330.1969.9515280

                        Published online: 29 Mar 2010.

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98                                                                        [MAR.

                                                               SEASONAL VARIATION IN PHYTOPLANKTON
                                                               FROM LAKE ROTORUA AND OTHER INLAND
                                                                    WATERS, NEW ZEALAND, 1966-67
                                                                                        VIVIENNE CASSIE

                                                                      Botany Department, The University of Auckland
                                                                              (Received for publication 10 June 1968)
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                                                            Between, May 1966 and May 1967, 110 preserved samples of the phytoplankton
                                                          of Lake Rotorua, New Zealand, were examined. Species and cell counts have
                                                          been compared with data from Lakes Rotoiti (21 samples) and Ohakuri (36 net
                                                          samples). Brief comparisons have also been made with the flora of two of the
                                                          Wellington City reservoirs and the oxidation ponds at Mangere, Auckland. In
                                                          Lake Rotorua the autumn, maximum was more pronounced than the spring
                                                          maximum. Cell numbers inshore at Kawaha Point were consistently lower than
                                                          those further out in the open lake. The phytoplankton is classified as a eutrophic
                                                          formation of the diatom type, with Chlorophyceae as main subordinates.
                                                          Dominants include Melosira granulata Ralfs (winter, spring, and autumn),
                                                          Melosira distans (Ehr.) Kütz. (spring, summer, and autumn), and Asterionella
                                                          formosa Hass. (summer and autumn).


                                                             Initially this study was planned to observe the effect on phytoplankton
                                                          of aerial spraying with 0.5 ppm of diquat of a 100-acre area in Lake
                                                          Rotorua heavily infested with Lagarosiphon major (Cassie 1967).
                                                          Sampling was continued from May 1966 to May 1967. Samples were
                                                          examined from the treated area of the lake and also from other areas
                                                          so that information on the phytoplanktonic cycle could be obtained.
                                                          Knowledge about the seasonal variation of phytoplanktonic organisms
                                                          is basic to an understanding of the entire plant and animal populations
                                                          since the phytoplankters are the primary producers and constitute the
                                                          first level in the food chain. Data from observations made over a single
                                                          year cannot show the whole pattern of rise and fall in abundance of
                                                          species, but they will serve as a basis for comparison with longer-term
                                                             Little work has been done on the phytoplankton populations of New
                                                          Zealand lakes. The few relevant surveys include those of Flint (1938)
                                                          for Lake Sarah, in the South Island; Jolly (1959) for several North and
                                                          South Island lakes; and Cunningham, Moar, Torrie, and Parr (1953)
                                                          for some North Island coastal dune lakes. Haughey (1965) has made
                                                          an intensive study of the seasonal variation of phytoplankton in sewage
                                                          treatment plants in the vicinity of Auckland. Reid (1964) has con-
                                                          tributed to the knowledge of fluctuations in volume of phytoplankton
                                                          N.Z. Jl mar. Freshwat. Res. 3: 98-123.

                                                          in Lake Rotorua. He attempted to evaluate effects of local factors on
                                                          eutrophication, noting the occurrence of spectacular blooms and the
                                                          organisms causing them. Finally Thomasson (1960) has described the
                                                          planktonic Staurastra of several North Island lakes, including Rotorua
                                                          and Rotoiti.


                                                             In Lake Rotorua samples were collected from three different sites
                                                          (Fig. 1). Station 1 was located in the area sprayed with diquat at
                                                          Kawaha Point. Station 2, the Open Lake Station, was sampled at the
                                                          surface, at a depth of 9 m, and near the bottom (17 m). This site is
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                                                          only a few chains east of the station investigated by Reid (1964) in
                                                          1963 and 1964. Station 3, a control site for Station 1, was at first an
                                                          area heavily infested by weed unaffected by any influence due to chemical
                                                          spraying. All samples were precisely of 200 ml. Those from Stations 1
                                                          and 3 were collected from a plastic tube extending from surface to
                                                          bottom (cf. Lund 1949). This core of water was thoroughly mixed
                                                          before the samples were collected.
                                                            Samples from Station 2 were taken from a Ruttner bottle. Plankton
                                                          organisms in water samples were fixed by adding 2 ml of a solution of
                                                          iodine-potassium iodide. Cells were allowed to settle out in polythene
                                                          bottles for 4-5 days. The supernatant liquid was then slowly drawn off
                                                          with an upturned siphon. The settled plankton was tipped into 4 in. X 1 in.
                                                          glass tubes and again allowed to sink for 2-3 days, after which the
                                                          supernatant was carefully reduced to 2 ml. Very dense samples were

                                                           SPRAYED AREA

                                                                             FIG. 1—Locality map and sampling sites.

                                                          concentrated to 20 ml. Counting was carried out, at first under bright
                                                          field, with a binocular microscope (Cooke, Troughton, and Sims)
                                                          and, later, with a phase contrast microscope (Reichert Zetopan).
                                                          Photomicrographs were taken with photo-automatic camera attachments
                                                          to fit the phase contrast microscope.
                                                             From the 2 ml (or 20 ml) concentrate an aliquot of 0.2 ml was drawn
                                                          off with a 5 ml pipette and loaded drop by drop into a Palmer-Maloney
                                                          counting chamber. Half the area was counted and results were expressed
                                                          as numbers of cells per litre. The remaining half was checked for
                                                          organisms not already recorded in the count. One subsample was counted
                                                          from each sample. Individual cells of unicellular, colonial, and filamen-
                                                          tous species each received a single count, but for Anacystis and Botryo-
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                                                          coccus each colony was noted, and for Oscillatoria, each filament. Such
                                                          a method allowed for the recording of the maximum number of sub-
                                                          ordinate species (except those flagellates disintegrated by the preser-
                                                          vative) and enabled a picture to be built up of the flora as a whole.


                                                          ENVIRONMENTAL FACTORS

                                                             Although no figures are available for the full year to indicate changes
                                                          in chemical content of the water, records were kept of water temperatures
                                                          at the site of the open lake station (Fig. 2). Figures for rainfall and
                                                          hours of sunshine have been taken from records made by the Meteoro-
                                                          logical Service at Whakarewarewa, near Rotorua.

                                                          < 16


                                                                                                           O   O BOTTOM (I7M)

                                                                 -A-JL4   hi   k\K   k   \k   A_L*   k\k

                                                          FIG. 2—Surface and bottom temperatures at open lake station from 14 May 1966
                                                                                       to 19 May 1967.
1969]      CASSIE—SEASONAL VARIATION IN PHYTOPLANKTON                     101

                                                                                    Temperature (Fig. 2)

                                                            Surface temperatures at the open lake station ranged from 8.2°c in
                                                          August to 21.3°c in late February. In winter, early spring, and late
                                                          autumn, conditions were isothermal from surface to bottom; but in
                                                          spring and summer (from October to March) surface values tended to
                                                          be slightly higher than those at the bottom (up to 2°c higher on 9
                                                          February 1967). On 30 March 1967 an isothermal temperature of 18.7°c
                                                          was noted at the open lake station, but no samples of phytoplankton were
                                                          obtained on this date. Conversely, no temperature is available for the
                                                          sampling date of 28 June 1966. Despite such occasional surface heating,
                                                          Lake Rotorua does not appsar to have a distinct epilimnion and
                                                          hypolimnion (Dr G. R. Fish, pers. comm.).
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                                                                               Rainfall and Hours of Sunshine

                                                            February 1967, the month with the heaviest rainfall, was also the
                                                          month with the most sunshine (Table 1). These conditions coincided
                                                          with peak production of the diatom Asterionella formosa (see p. 106).

                                                          TABLE 1—Monthly rainfall and hours of sunshine at Whakarewarewa from May 1966
                                                                                           to May 1967
                                                                                                Rainfall   Hours of
                                                                                                 (in.)     sunshine
                                                                            May 1966             3.96       165.5
                                                                            June 1966            6.27       111.7
                                                                            July 1966            8.72       141.6
                                                                            August 1966          4.32        161.3
                                                                            September 1966       6.26        143.6
                                                                            October 1966         3.47        199.2
                                                                            November 1966        6.96        143.5
                                                                            December 1966        4.47        180.0
                                                                            January 1967         2.66        195.1
                                                                            February 1967        9.79       202.9
                                                                            March 1967           6.04        148.8
                                                                            April 1967           1.75       155.5
                                                                            May 1967             4.62       136.2

                                                             In each of the 110 samples examined, 20-30 different phytoplankters
                                                          were usually listed (Appendix I). Zooplankters were scarce, never more
                                                          than 4 species being found in any one sample, and then usually less
                                                          than 10 of each. Numbers of species varied in different parts of the lake
                                                          on the same day. For instance, on 20 January 1967 a minimal number
                                                          was recorded for the surface of the open lake station (11 plants and 1
                                                          animal), while at Kawaha Point there were 32 plants and 1 animal, the
                                                          greatest number of species listed in any one sample. The total number
                                                          of cells per litre in this sample, however, was less than half that recorded
                                                          at the other stations on the same day.
102       N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH                       [MAR.

                                                          QUALITATIVE AND QUANTITATIVE RESULTS

                                                            The dominant phytop'ankters in Lake Rotorua are the diatoms.

                                                          TOTAL SURFACE PHYTOPLANKTON (Fig.              3)

                                                             In general, a similar trend was apparent at each sampling site. Figures
                                                          from Kawaha Point were nearly always lower than those from the
                                                          other two stations, where the spring maximum in August did not much
                                                          exceed 2 X 106 cells per litre. (Figures for bottom and middle depths
                                                          were slightly greater.) The autumn figures were more than twice as
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                                                          high, over 5 X 106 cells per litre in the open lake (9 m). The corres-
                                                          ponding figure for Kawaha Point was nearly seven times less. By April
                                                          1967 cells at the bottom of the open lake station exceeded those at the
                                                          surface and middle layers. Off Mokoia Island autumn maxima were
                                                          even greater than those at different depths in the open lake.

                                                          FIG. 3—Total cells per mi'llilitre at surface from May 1966 to May 1967 at three
                                                               different stations. (The broken line in counts from off Mokoia Island indicates
                                                               a change in the sampling site to a more heavily weed-infested area.)

                                                          DOMINANT SPECIES

                                                             Throughout most of the sampling year the bulk of the flora was
                                                          formed by filaments of a large, drum-shaped, chain-forming, centric
                                                          diatom Melosira granulata (Fig. 5), but at times it was superseded by
                                                          star-shaped colonies of a pennate diatom Asterionella jormosa (Fig. 4).
                                                          Yet another species of Melosira, M. distans, may co-dominate, its chains
                                                          being so small that its true ecological position is hard to assess accurately.
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                                                                     FIG. 4—Asterionella formosa Hass. Film 3/31. X412.
                                                                       FIG. 5—Melosira granulata Ralfs. Film 6/13. X 900.
                                                                      FIG. 6—Botryococcus braunii Kutz. Film 3/30. X 412.
                                                          FIG. 7—Pediastrum duplex var. gracillimum West and West, with Melosira
                                                                      granulata var. angustissima O. Mull. Film 5/14. X 487.
                                                                        FIG. 8—Peridinium striolatum Playf. 4/1. X 412.
                                                                 FIG. 9—Cystodinium comifax (Schillg.) Klebs. Film 2/1. X 660.
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                                                              FIG. 10—Staurodesmus Ieptodermus (Lund) Teiling. Film 6/18. X 900.
                                                          FIG. 11—Staurastrum anatinum i. longibrachiatum (West and West) Film
                                                                                          4/15. X 660.
                                                                            FIG. 12—Cosmocladium sp. Film 1/7. X 412.
                                                                    FIG. 13—Actinastrum hantzschii Lagerh.. Film 4/17. X 487.
                                                                  FIG. 14—Staurodesmus dickiei (Ralfs) Lillier. Film 6/14. X 900.
                                                                       FIG. 15—Staurastrum muticum Breb. Film 4/6. X 660.
1969]        CASSIE—SEASONAL VARIATION IN PHYTOPLANKTON                              105

                                                          Subordinate species (Figs 6-15) belong mainly to the green algae
                                                           (Table 2). Many of these, including species of Staurastrum, Staurodes-
                                                          mus, Cosmarium, and Closterium, are relatively scarce although their
                                                          cells, especially those of Staurastrum, are often larger and more conspic-
                                                          uous than those of the dominants. Other Chlorophyceae such as
                                                          Mougeotia, Dictyosphaerium, and Actinastrum are sufficiently abundant
                                                          to warrant their classification as subdominants (up to 2 X 105 cells per
                                                          litre). Botryococcus and Pediastrum are not common. With the possible
                                                          exception of Peridinium striolatum, Dinophyceae are not known to be
                                                          ecologically significant in this lake. Ceratium hirundinella and Cysto-
                                                          dinium cornifax occur only sporadically and in small numbers.
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                                                          TABLE 2—Seasonal variation in numbers of species belonging to different algal classes*

                                                                  Class              10.6.66         7.9.66          1.12.66         26.2.67

                                                          Chlorophyceae                14              11              13              15
                                                          Bacillariophyceae             6               4               4               7
                                                          Chrysophyceae                                 1               1
                                                          Dinophyceae                                   2               2               '3
                                                          Myxophyceae                   i               1               3                3
                                                          Other groups                  2               4               1                4

                                                          Dominant species:     Asterionella    Melosira        Melosira        Asterionella
                                                                                 formosa          granulata       granulata       formosa
                                                                                Melosira        Melosira        Asterionella    Mougeotia sp.
                                                                                  granulata       distans        formosa        Melosira
                                                                                                Dinobryon sp.   Actinastrum       granulata
                                                                                                Anabaena          hantzschii    Melosira
                                                                                                  circinalis                      distans
                                                          T h e dates are identical with those selected for illustration of cell numbers and tem-
                                                           peratures from different depths at the open lake station. See Table 3 and Fig. 19.

                                                          Melosira granulata (Fig. 16): Samples for the 8 months showed this
                                                          species to be consistently dominant and graphs of its abundance followed
                                                          closely those for total number of cells at the surface. From mid January
                                                          there was a sharp decrease. By 27 February 1967 a minimum of 13,000
                                                          cells per litre was reached at the open lake station, and only 4,000 per
                                                          litre were recorded from Kawaha Point. Most of the Melosira filaments
                                                          present in the phytoplankton had sunk to the bottom on this date
                                                          (270,000 per litre).
                                                             Melosira granulata soon regained prominence in late autumn at the
                                                          open lake station and off Mokoia Island. Recovery was slower at Kawaha
106       N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH                                         [MAR.

                                                                                                                            • KAWAHA PT.
                                                                                                                            O OPEN LAKE (SURFACE)
                                                                                                                            X MOKOIA ].             X.      X
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                                                                     A   4L    A _LA-_i   Li     A IA   Al A   A   A   LX

                                                          FIG. 16—Melosira granulata: Cells per millilitre at surface from May 1966 to
                                                              May 1967 at three different stations. (The broken line in counts from off
                                                              Mokoia Island indicates a change in the sampling site to a more heavily
                                                              weed-infested area.)

                                                                         • KAWAHA PT.
                                                                         O OPEN LAKE (SURFACE)
                                                                         X MOKOIA 1.

                                                          FIG. 17—Asterionella jormosa: Cells per millilitre at surface from May 1966 to
                                                              May 1967 at three different stations. (The broken line in. counts from off
                                                              Mokoia Island indicates a change in the sampling site to a more heavily
                                                              weed-infested area.)

                                                          Asterionella jormosa (Fig. 17): Two maxima were recorded. The first
                                                          was in mid winter, when cell numbers did not exceed 254 per millilitre.
                                                          The second, in early autumn, and nearly 15 times as great, lasted from
                                                          late February to early March. Asterionella was, however, a major con-
                                                          tributor to the total phytoplankton for nearly 3 months (January to
                                                          April). Cell numbers at the open lake station and Mokoia Island were
1969]      CASSIE—SEASONAL VARIATION IN PHYTOPLANKTON                     107

                                                          in fairly close agreement for most of the sampling year. At Kawaha
                                                          Point numbers were slightly less except at times of peak production,
                                                          when they were six times less than those at the open lake station (sur-
                                                          face) . At no time were Asterionella colonies completely absent from the

                                                          Melosira distans (Fig. 18): Minute 2-4-celled chains, not more than
                                                          6-8/x in diameter, abounded in the samples from all three stations for
                                                          most of the year. Cell numbers did not usually exceed 400 per millilitre.
                                                          Three peaks of abundance occurred: in spring, summer, and autumn.
                                                          Surface estimates did not differ markedly from one site to another.
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                                                                         O OPEN LAKE (SURFACE)
                                                                         X MOKOIA I.

                                                          FIG. 18—Melosira distans: Cells per millilitre at surface from May 1966 to
                                                              May 1967 at three different stations. (The broken line in counts from off
                                                              Mokoia Island indicates a change in the sampling site to a more heavily
                                                              weed-infested area.)

                                                          Vertical Distribution of Phytoplankton in the Open Lake Station (Figs
                                                          19 and 20): Records of total cell numbers per millilitre at the surface,
                                                          9 m deep, and 17 m deep show that there was a more or less uniform
                                                          vertical distribution of phytoplankton at this site throughout the sampling
                                                          year. It cannot be stated that cell numbers were always higher at the
                                                          surface or below. Some variation occurred, although it does appear from
                                                          vertical distribution of Melosira granulata that filaments of this species
                                                          are generally more numerous on the bottom (cf. Lund 1964, 1955; Fish
                                                             Curves for M. granulata at all three depths formed the bulk of total
                                                          cell numbers through spring and summer until mid February, when,
                                                          as in other parts of Lake Rotorua, they fell off rapidly with the blooming
                                                          of Asterionella.
                                                          Records for 4 Representative Days: The pattern of vertical distribution
                                                          at the open lake station of the three dominant diatoms on 4 separate
108        N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH                        [MAR.

                                                          1.000 I—

                                                                                                                   DI7 METRES (BOTTOM)
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                                                                                         L_1A                IA   A I A        A   IA
                                                                                          O                                        A

                                                          FIG. 19—Total cells per millilitre at open lake station from May 1966 to May
                                                                        1967 at three different depths (surface to bottom).

                                                                                                                      D SURFACE
                                                                                                                      O 9 METRES
                                                                                                                      B 17 METRES (BOTTOM)

                                                          FIG. 20—Melosira granulata: Cells per millilitre at open lake station from three
                                                                                        different depths.

                                                          days (10 June, 7 September, 1 December 1966, and 27 February 1967),
                                                          each day representing a different season, is shown in Fig. 21. In winter,
                                                          spring, and early summer cell counts of Melosira granulata, M. distans,
                                                          and Asterionella jormosa showed a more or less even pattern of abun-
                                                          dance from surface to bottom. During most of this time temperatures
                                                          were isothermal. As surface layers became warmer, stratification of
                                                          phytoplankton became more evident. By late February, when Asterio-
                                                          nella was all pervading between 0 and 17 m, surface temperatures were
                                                          up to 1.6°c higher than those at the bottom (Table 3). Although no
                                                          distinct thermocline has been reported for Lake Rotorua, the Asterio-
                                                          nella bloom, which arose with the warming up of the surface water
                                                          layers, is evidence of a certain degree of stability of the water column.
1969]      CASSIE—SEASONAL VARIATION IN PHYTOPLANKTON                        109

                                                                            M. GRANULATA        A. FORMOSA
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                                                                   FIG. 21—Vertical distribution at open lake station of Melosira
                                                                        granulata, Asterionella formosa, and M. distans in four
                                                                        different seasons, at three depths, on 4 single days.

                                                          TABLE 3—Temperatures at three depths from surface to bottom on 4 separate days in
                                                                               different seasons at open lake station

                                                                          Depth       10.6.66    7.9.66      1.12.66   27.2.67
                                                                           (m)         (°c)       (°c)         (°c)     (°c)

                                                                             0         10.8        9.5        16. 4     21 .3
                                                                             9         10.8        9.5        15. 9     21 .1
                                                                            17         10.8        9.5        15. 8     19 .7

                                                          SUBORDINATE SPECIES (Fig.      22)

                                                              Among the large numbers of less important species, most frequent
                                                          were Mougeotia sp., Anabaena circinalis, and Dinobryon cylindricum*
                                                          Long, slender filaments of Mougeotia were minor constituents of the
                                                          phytoplankton from May to October. They disappeared until January,
                                                          when there was an upsurge to 200,000 cells per litre, and remained
                                                          quite conspicuous until mid May, the end of the sampling year. Spiral
                                                          coils of the blue-green alga Anabaena, also scarce in winter and spring,
                                                          suddenly increased in mid summer to a peak of about 267,000 cells per
                                                          litre. They disappeared just as suddenly 3 weeks later. More sporadic
                                                          in appearance was Dinobryon, a colonial chrysophyte, which increased
                                                          slightly during October as Mougeotia faded out. It made only a tran-
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                                                          sitory increase from January to March and was relatively unimportant
                                                          in the total phytoplankton.

                                                          FIG. 22—Abundance of Mougeotia, Anabaena, and Dinobryon spp. at open lake
                                                                                     station (surface).

                                                              Species more sporadic in appearance and fewer in cell numbers in-
                                                          cluded: Actinastrum hantzschii, Synedra ulna, Closterium aciculare,
                                                          Dictyosphaerium pulchellum, the small Cosmarium contractum var.
                                                          ellipsoideum, species of Staurastrum (mainly S. smithii f. triradiatum,
                                                          S. muticum, and S. leptocladum var. elegans), and Staurodesmus
                                                          (S. triangularis, S. leptodermus, and S. dickiei) {see Appendix II for
                                                          a list of species identified in this survey).

                                                          *Dr J. Lund identified this species as Dinobryon sertularia Ehr. (Jolly 1959,
                                                           p. 58) but Thomasson (1960) lists D. cylindricum Imh. and D. divergens Imh.
                                                           as subdominants in Lake Rotorua during October 1955.

                                                            Naumann's (1931) classification of the phytoplankton has been
                                                          favourably reviewed by Hutchinson (1967), but the latter points out
                                                          that there is no place in Naumann's scheme for the ecologically im-
                                                          portant genus Asterionella. To conform with Hutchinson's ideas, it
                                                          seems logical to classify the phyloplankton flora of Lake Rotorua as
                                                          a eutrophic formation of the diatom {Melosira spp.-Asterionella) type,
                                                          dominated by the Melosira granuIata-M. distans-Asterionella formosa
                                                          association. The subordinate members of this community are mainly
                                                          chlorophycean, with occasional abundance or even dominance of the
                                                          myxophycean Anabaena circinalis and the chrysophycean Dinobryon
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                                                                              COMPARISON WITH OTHER LAKES

                                                             The value of the survey of Rotorua phytoplankton has been enhanced
                                                          by comparing it with phytoplankton in four other bodies of water, each
                                                          of a distinctive type:
                                                          1. A less eutrophic lake—Lake Rotoiti.
                                                          2. A "hydro-electric" lake with pronounced movement of water—Lake
                                                          3. Two reservoirs supplying Wellington City—Morton Dam, Wainui-
                                                          omata, and the upper Karori reservoir.
                                                          4. Moderately and extremely polluted oxidation ponds—Mangere Treat-
                                                          ment Plant, Auckland.

                                                          LAKE ROTOITI {see   Fig.   1)

                                                            Lake Rotoiti is long, narrow, and deep (maximum depth 90 m) and
                                                          connected by a narrow channel—the Ohau Channel—with Lake Rotorua.
                                                          Considerable amounts of water drain from Lake Rotorua into the west
                                                          end of Lake Rotoiti and from there discharges into the Kaituna River.
                                                          A distinct epilimnion and hypolimnion develop during the warmer parts
                                                          of the year, and a thermocline was evident from October 1966 until the
                                                          end of May 1967 (Dr G. R. Fish, pers. comm.). Twenty-one samples
                                                          were obtained from a site in Wrights Bay (at the surface, 4 m, and 8 m)
                                                          at fortnightly intervals from January to May 1967. Growth of the water
                                                          weed Lagarosiphon was not extensive under the site, which was about
                                                          91 m off shore. Each sample was analysed in the same way as those from
                                                          Lake Rotorua.

                                                          Total Cells per Litre: There is some evidence that, at least in summer
                                                          and autumn, the total phytoplankton in Lake Rotoiti is considerably
                                                          less than that in Lake Rotorua (Table 4). Total numbers of cells per
                                                          litre at and below the surface in Wrights Bay were mostly a factor of
                                                          10 below those at the Rotorua open lake station. The figures quoted lend
                                                          support to the view that the degree of eutrophication in Lake Rotoiti
                                                          is less marked than that in Lake Rotorua.
112        N.Z.   JOURNAL OF MARINE & FRESHWATER RESEARCH                     [MAR.

                                                          Dominant Species: Again the dominants were Melosira granulata,
                                                          M. distans, and Asterionella formosa, but in this lake cells of M. distans
                                                          outnumbered those of M. granulata by up to 12 times at the surface (6
                                                          February 1967). Filaments of M. granulata were relatively scarce and
                                                          only once (on 3 January 1967) at 4 m did they reach nearly 300 per
                                                          millilitre. Samples at 4 m and 8 m contained more filaments than those
                                                          at the surface in summer and autumn. Not until May (5 May 1967)
                                                          was this situation reversed, presumably after the relatively stabilised
                                                          water column had been broken up. The numbers of cells of Asterionella
                                                          reached their peak about the same time as in Lake Rotorua, but the
                                                          maximum number was nearly 18 times less than that at the Rotorua open
                                                          lake station (only 212 cells per millilitre on 17 February 1967).
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                                                          TABLE 4—Comparison between total cells per millilitre on comparable days at different
                                                                              depths in Lakes Rotorua and Rotoiti

                                                                         Lake Rotorua,
                                                                        Open Lake Station         6.1.67      27.2.67     2.5.67

                                                                              Surface             1,457       4,550        1,267
                                                                                9m                  964       4,074        1,336
                                                                               17 m               1,525       2,415          514

                                                                            Lake Rotoiti,
                                                                            Wrights Bay           3.1.67      27.2.67      5.5.67

                                                                              Surface               118         257          708
                                                                               4m                   290         438          168
                                                                               8m                   136         155          175

                                                             Less conspicuous members of the flora included Mougeotia, Dino-
                                                          bryon, and Anabaena, but all of these were sporadic in appearance and
                                                          sparse. Two distinct species of Anabaena were recognisable: larger cells
                                                          and spiral coils of A. circinalis, and very much smaller semicircular
                                                          threads of A. flos-aquae (not seen in samples from Lake Rotorua).
                                                          Species which achieved transitory peaks in abundance and could be
                                                          classed as subdominants included Peridinium striolatum, Dictyosphae-
                                                          rium pulchellum, Sphaerozosma aubertianum, and Actinotaenium (Cos-
                                                          marium) pyramidatum.
                                                             Peridinium striolatum, less abundant in Lake Rotorua, was quite
                                                          common in L. Rotoiti, where it appeared as dark balls up to 67ft in
                                                          diameter. It was the most obvious feature of the phytoplankton, though
                                                          sparse (Fig. 8).
                                                             Melosira granulata var. angustissima, in long, narrow, curved filaments
                                                          with sharp points at the ends, was also present in moderate numbers in
                                                          Lake Rotoiti. It likewise was scarce or absent in Lake Rotorua (Fig. 7).

                                                          LAKE OHAKURI (Fig.     23)
                                                             About 25 miles north of Lake Taupo, a 100-ft-wide dam with its
                                                          associated power station spans the Waikato River. The water south of
                                                          this dam forms Lake Ohakuri, a long, narrow, looped stretch—the old
                                                          river bed—extending in a north-easterly direction. The lake is mostly
                                                          about 30 m (in some parts up to 45 m) deep. It is heavily infested with
                                                          dense growths of the free-floating hornwort Ceratophyllum demersum,
                                                          which aids in the eutrophication process by preventing nutrients from
                                                          being lost to the continually flowing water (Hill 1967). A narrow stream,
                                                          the Whirinaki Stream, flows into Lake Ohakuri from 2 miles north-east,
                                                          near the dam. This drains rolling pasture grazed by sheep and is rich
                                                          in phosphate and nitrate. Hill (1967) reports up to five times as much
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                                                          phosphate in the Whirinaki Stream as in the main waters of Lake
                                                          Ohakuri. The lake itself has more eutrophic characteristics at the north
                                                          (dam) end than at the south (Taupo) end. Thirty-six net samples (200
                                                          meshes to the inch) were examined during summer and autumn of 1967.
                                                          These came from three stations:
                                                          l.Lake Ohakuri, north of Orakeikorako (north of the loop towards
                                                          Rotorua). Vertical hauls were made to 20 m, mid lake.
                                                          2. Whirinaki Stream, 2 miles north-east of main lake. Vertical hauls
                                                          were made to 5 m.
                                                          3. Lake Ohakuri, about 1 mile up stream from the dam. Vertical hauls
                                                          were made to 20 m, mid lake.
                                                              The water at Station 1 was mainly bluish, but contained a certain
                                                          amount of sediment. That in the Whirinaki Stream was often dis-
                                                          coloured by dense brown or green phytoplankton blooms. Among these
                                                          a Secchi disc would disappear at 1 m below the surface (Mr C. F. Hill,
                                                          pers. comm.).
                                                              Though a strict comparison with the phytoplankton of Lake Rotorua
                                                          was not possible, since the samples were gathered with a tow net, the
                                                          general features of the larger-celled species could be assessed. Abundance
                                                          was estimated on a 1:5 scale (cf. Cassie 1961). Salient features are:
                                                           1. Dominance of the narrow form of Melosira granulata (M. granulata
                                                          var. angustissima) at all three stations throughout summer and autumn.
                                                           The wider M. granulata was correspondingly scarce.
                                                           2. Local dominance of Asterionella jormosa near the dam. Cells of this
                                                           population were extremely large, more than twice as long as those in
                                                           colonies from Lakes Rotorua and Rotoiti (Fig. 4).
                                                          3. Local blooms in Whirinaki Stream of Anabaena circinalis and Pedia-
                                                           strum duplex var. gracillimum (Fig. 7) (January 1967) and Volvox
                                                           tertius (April 1967). Though common at the same time in the main
                                                           lake, none of these species achieved the vast numbers that discoloured
                                                           the rich, undisturbed waters of the tributary. Volvox has not been found
                                                           by the writer (though it may well be present) in Lake Rotorua, and
                                                           Pediastrum is scarce. Anabaena did not bloom in either Lake Rotorua
                                                           or Lake Rotoiti at the time of its upsurge in Lake Ohakuri.
                                                           4. Local abundance, even subdominance, of Dinobryon and Botryo-
                                                           coccus braunii, especially near the dam.
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                                                                     FIG. 23—Map of the northern end of Lake Ohakuri,
                                                                                 showing sampling sites.

                                                          5. Common subordinate algae included a mainly chlorophycean assem-
                                                          blage: Eudorina elegans, Pandorina morum, Staurastrum longiradiatum,
                                                          and Synedra sp.
                                                          6. Species were recorded which have not been found by the writer in
                                                          either Lake Rotorua or Lake Rotoiti: Botryococcus protuberans,
                                                          Geminella minor, Oocystis pusilla, Pandorina morum, Selenastrum
                                                          gradle, Volvox sp., and Melosira undulata.

                                                          WELLINGTON CITY RESERVOIRS
                                                            Estimations of the phytoplankton of two major sources of Wellington's
                                                          water supply—the Morton Dam at Wainuiomata and the upper and lower
                                                          reservoirs at Karori—have been made available to the writer.
                                                          (a) Morton Dam, Wainuiomata: Within the period        of sampling in Lake
                                                          Rotorua no major bloom was reported of species of     Melosira or Asterio-
                                                          nella. However, just before the time of sampling, a   bloom of M. granu-
                                                          lata var. angustissima did occur. On 18 March         1966 maximum cell
1969]      CASSIE—SEASONAL VARIATION IN PHYTOPI.ANKTON                      115

                                                          numbers in a depth of 10 ft "before the strainer" were estimated at
                                                          > 4 X 106 cells per litre. Other species of Melosira were abundant all
                                                          year at the surface, but only sporadic in deeper layers. Asterionella was
                                                          rare, but a Cyclotella achieved a winter abundance of up to > 5 X 105
                                                          cells per litre.

                                                          (b) Upper Karori Reservoir: Here a variety of Melosira spp. replaced
                                                          M. granulata var. angustissima. They were recorded in considerable
                                                          numbers at the surface, with peaks in April and August of 2,000 and
                                                          2,880 eel's per litre respectively. Cyclotella was the dominant diatom;
                                                          it was never absent at the surface and reached a maximum of over
                                                          5 X 1 0 ° cells per litre in September and January. Even greater numbers
                                                          (8 X 10


                                                             Lake Rotorua, which covers an area of 26 square miles, is greatly
                                                          enriched by an inflow of nutrients from aerial topdressing, storm water,
                                                          land drainage, sewage, and septic tanks (Reid 1964). Large quantities
                                                          of nutrients have been locked up in the massive growths of Lagarosiphon
                                                          and Elodea. It has been stated that where growth of aquatic plants is
                                                          extensive there is less phytoplankton, as in Lake Maraetai (Reid 1964)
                                                          and Lake Rotoiti (Fish 1966). One would expect, therefore, to find
                                                          less phytoplankton in the heavily weed-infested area off Mokoia Island
                                                          and more phytoplankton in the open water of Lake Rotorua. One might
                                                          also expect more phytoplankton in the Kawaha Point area where spray-
                                                          ing had killed the weeds. The release of nutrients after spraying could
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                                                          perhaps have promoted intense blooms of phytoplankton. Such indeed
                                                          occurred after spraying in an arm of Te Weta Bay, Lake Rotoiti (Fish
                                                           1966). However, the two areas cannot be compared in this respect,
                                                          since Te Weta Bay is isolated from the main body of water in Lake
                                                          Rotoiti. Further, spraying took place at a different season. Kawaha
                                                          Point on the other hand is not a separate arm of Lake Rotorua, but
                                                          forms part of the waters of the main lake, which are comparatively well
                                                          mixed. In such a situation localised blooms of phytoplankton are unlikely
                                                          to occur. Spraying in the Kawaha Point area in May 1966 undoubtedly
                                                          killed the weed. Regeneration of green shoots was not reported until
                                                          5 months later (Chapman 1967). Nearly 18 months after the spraying
                                                          there are still only isolated centres of growth of Lagarosiphon, but the
                                                          weed is disappearing in other parts of the lake of its own accord regard-
                                                          less of effects due to spraying (Dr G. R. Fish, pers. comm.).
                                                             Results from cell counts in the present survey show that there were
                                                          consistently fewer phytoplankters near Kawaha Point than there were
                                                           both at the open lake station and among fairly dense weed off Mokoia
                                                             According to Matthews (1967) intense algal blooms would not be
                                                          expected after spraying with 0.5 ppm of diquat, even over a large area,
                                                          if the spraying were carried out in May (late autumn) when "cooler
                                                           water temperatures, higher water movement and more water being
                                                           present, the released nutrients would tend to be flushed from the lakes
                                                           before optimum algal growth in the warm summer months".

                                                                                     Melosira granulata
                                                            A meroplanktonic form, Melosira granulata is classed by Lund (1954)
                                                          as a species with a relatively high demand for light and temperature
                                                          and one that can survive under anaerobic conditions by means of resting
                                                          spores in bottom deposits. Hustedt (1945) believes this species to be
                                                          the most characteristic planktonic diatom of eutrophic waters in Europe.
                                                          Dominance of M. granulata has been reported by other New Zealand
                                                          workers. Jolly's (1959) results in 1955-56 from Lake Rotorua showed
                                                          that it was dominant for almost the entire year, with winter and spring
                                                          maxima (July and August) when it formed 88-97% of the total phyto-
                                                          plankton. All other species were scarce or only locally abundant, except

                                                           a species of Cosmarium. Later, in 1963-64 Reid (1964) again found
                                                           peak production of M. granulata to occur in August in the same lake.
                                                           These records and the data in the present survey show that the behaviour
                                                           of Melosira granulata in a shallow temperate lake in the Southern
                                                          Hemisphere, such as Lake Rotorua, is essentially similar to that of its
                                                          Northern Hemisphere counterpart.
                                                             Both Lund (1954) for English lakes, and Fish (1957) for Lake
                                                           Victoria in Africa, related the numbers of Melosira filaments to the
                                                          degree of turbulence of the water column. Large populations occurred
                                                          in these lakes only when thermal stratification no longer existed. Con-
                                                           versely, cell numbers were found to decrease with increasing stability
                                                          of the water, and numbers of living frustules increased at the bottom.
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                                                          In Lake Rotorua a similar trend was apparent among planktonic fila-
                                                          ments of M. granulata in summer, when, as thermal stratification
                                                          occurred, cell numbers increased toward the bottom (Fig. 21).
                                                             Two protozoans were observed living attached to filaments of Melosira
                                                          granulata. At most times of year a Vorticella was common. A growth
                                                          of urn-shaped Pyxidium cells was restricted to autumn samples. Neither
                                                          organism occurred in sufficient numbers to have an adverse effect on the
                                                          population as a whole.

                                                                                    Asterionella formosa
                                                             Hutchinson (1967) regards A. formosa as probably one of the few
                                                           truly euplanktonic forms among the phytoplankton, most of which have
                                                          an origin from the bottom. Asterionella has been recorded as a member
                                                          of both oligotrophic and eutrophic formations, oligotrophic in the large
                                                          lakes of Canada (Rawson 1956) and eutrophic in most temperate
                                                          regions of the world (Hutchinson 1967). Lund (1949) found in the
                                                          English lakes that live cells of A. formosa were always present in the
                                                          open water and, given adequate light and nutrients, growth would occur.
                                                          No resting stage was observed. From detailed records over a consecutive
                                                          period of years Lund found A. formosa produced greater spring and
                                                          smaller autumn maxima, with up to 5 X 107 cells per litre.
                                                              By contrast, in Lake Rotorua A. formosa did not reach its peak until
                                                          late summer and early autumn. Its abundance was greatest when the
                                                          water column was more stabilised and when M. granulata filaments had
                                                          sunk to the bottom. Reid (1964) found Asterionella to be "very numer-
                                                          ous" in March 1964, but when Jolly (1959) sampled in Lake Rotorua
                                                          in 1955-56, it was never a major constituent of the centrifuged phyto-
                                                          plankton and often constituted 1% of the whole sample.
                                                             Data for a single year, therefore, do not necessarily show the complete
                                                          range of variation in dominance of the different species. Anabaena, for
                                                          example, was never present in the samples collected in 1966-67 from
                                                          Rotorua in quantities greater than 313,000 cells per litre, although Reid
                                                          described a bloom in October 1964 which covered many square miles
                                                          of the lake surface. Furthermore, with the methods used in the present
                                                          survey it was not possible to study fluctuations in abundance of the
                                                          micro-flagellates which could not be preserved.
118       N.Z. JOURNAL OF MARINE & FRESHWATER RESEARCH                   [MAR.

                                                                                        Melosira distans
                                                             The importance of this tiny celled diatom is not easy to assess. High
                                                          in cell numbers but small in cell volume, it could quite easily be over-
                                                          looked altogether, depending on the technique of counting. One of the
                                                          main differences between Lakes Rotorua and Rotoiti appears to lie in
                                                          the more frequent occurrence of M. distans in the latter. The phyto-
                                                          plankton of Lake Rotoiti bears some similarity, at least in summer and
                                                          autumn, to that of Finnish lakes, where Jarnefelt (1956) has reported
                                                          in clear unproductive lakes an association of Melosira distans with
                                                          Dinobryon spp. and often Cycloteila stelligera and C. kutzingiana.
                                                          Dinobryon and Cycloteila stelligera are frequent in Lake Rotoiti, with
                                                          M. distans, M, granulata, and Asterionella.
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                                                             The phytoplankton of Lake Rotorua emerges as a moderately eutrophic
                                                          assemblage dominated by diatoms and with mainly Chlorophyceae as
                                                          subordinates. Reduced cell numbers at Kawaha Point may initially
                                                          have been a result of spraying the surface of this area with diquat, but
                                                          long after the spray had lost effect, phytoplankters continued to be
                                                          scarcer here than in the open lake. The reason for this remains obscure
                                                          at present. In fact it could be simply an effect of sampling close inshore.
                                                             Surface and intermediate depths at the Lake Rotorua open lake
                                                          station consistently displayed cell numbers higher by a factor of 10
                                                          than those from an inshore station in Lake Rotoiti. Such figures imply
                                                          a higher degree of eutrophication in the former lake. However, a com-
                                                          parison of cell numbers per millilitre in Lake Rotorua with those from
                                                          much more heavily polluted bodies of water such as the oxidation ponds
                                                          at Mangere, Auckland, shows that Lake Rotorua is less rich in cells
                                                          of species common to both, such as Actinastrum hantzchii and Anacys-
                                                          tis cyanea, by up to a factor of 104. The most obvious difference from
                                                          a "hydro-electric" lake planktonic flora, such as that in Lake Ohakuri
                                                           (where water movement is much more pronounced), is in the dominance
                                                          of the wide form of M. granulata. In Lake Ohakuri, as in the Morton
                                                          Dam, Wainuiomata, the narrow form, the so-called M. granulata var.
                                                          angustissima (see Cassie 1961, PI. V, figs 1-3), is by far the commonest
                                                          phytoplankter. Thomasson (1960) notes that M. granulata in Lake
                                                          Rotorua is an unusual form with large pores but lacking the usual
                                                          terminal spines.


                                                             The writer wishes to express her indebtedness to the following, without whose
                                                          oo-operation this work would not have been possible: the Marine Department
                                                          for financial assistance; the Research Grants Committee for a grant to provide
                                                          microscope and camera equipment; the Electricity Department for permission
                                                          to publish part of a map of Lake Ohakuri; the New Zealand Meteorological
                                                          Service for supplying rainfall and sunshine data; Mr G. D. Waugh for assistance
                                                          with publication; Dr G. R. Fish for arranging collecting of samples from Lakes
                                                          Rotorua and Rotoiti and for valuable advice and criticism of the manuscript;
                                                          Mr I. Johnstone and Dr Mary Allessio for assistance with the collecting; Mr
                                                          C. F. Hill for net samples from Lake Ohakuri; Mr I. L. Vidal for supplying data
                                                          from Wellington City reservoirs; Mr C. T. Webb for draughting the figures;
                                                          Miss Helen Cameron, 'for concentrating the samples; Mr J. F. Lyon for technical
1969]      CASSIE—SEASONAL VARIATION IN PHYTOPLANKTON                                       119

                                                          assistance with the photomicrography; Dr K. Thomasson for help with iden-
                                                          tifications of phytoplankton; Dr Ann Chapman for identifying zooplankton;
                                                          Dr T. Brown for identifying Protozoa; Dr R. M. Cassie for criticism of the
                                                          manuscript; and Professor V. J. Chapman, who instigated the research and in
                                                          whose department the work was carried out.

                                                          CASSIE, V. 1961: Marine phytoplankton in New Zealand waters. Botanica mar.
                                                                    2. Suppl. 54 pp.
                                                             ——1967: Effects of spraying on phytoplankton in Lake Rotorua, 1966.
                                                                    In Chapman, V. J. and Bell, C. A. (Eds.), "Rotorua and Waikato
                                                                    Water Weeds: Problems and the Search for a Solution", pp. 31-9.
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                                                                    Department of University Extension, the University of Auckland,
                                                          CHAPMAN, V. J. 1967: General report. In Chapman, V. J. and Bell, C. A. (Eds.),
                                                                    "Rotorua and Waikato Water Weeds: Problems and the Search for
                                                                    a Solution", pp. 1-14. Department of University Extension, the Univer-
                                                                    sity of Auckland, Auckland.
                                                          CUNNINGHAM,    B.   T.,   MOAR, N.   T.,   TORRIE, A.   W.,   and   PARR, P.   J.   1953:    A
                                                                     survey of the western coastal dune lakes of the North Island, New
                                                                      Zealand. Aust. J. mar. Freshwat. Res. 4: 343-86.
                                                           FISH, G. R. 1957: A seiche movement and its effect on the hydrology of Lake
                                                                      Victoria. Fishery Publs colon. Off. 10. 68 pp.
                                                                   1966: Some effects of the destruction of aquatic weeds in Lake Rotoiti,
                                                                     New Zealand. Weed Res. 6: 350-8.
                                                          FLINT, E. A. 1938: A preliminary study of the phytoplankton in. Lake Sarah
                                                                      (New Zealand). J. Ecol. 26: 353-8.
                                                          HAUGHEY, A. 1965: Phytoplankton in sewage treatment ponds (M.Sc. thesis
                                                                     lodged in the University of Auckland library.)
                                                          HILL, C. F. 1967: Investigation of the weed problem at Lake Ohakuri. In
                                                                     Chapman, V. J. and Bell, C. A. (Eds.), "Rotorua and Waikato Water
                                                                     Weeds: Problems and the Search for a Solution", pp. 15-18. Depart-
                                                                     ment of University Extension, the University of Auckland, Auckland.
                                                          HUSTEDT, F. VON B. 1945: Die Diatomeenflora Norddeutscher Seen mit besonderer
                                                                     Berücksichtigung des Holsteinischen Seengebiets. Arch. Hydrobiol. 41:
                                                          HUTCHINSON, G. E. 1967: "A Treatise on Limnology. Vol. II. Introduction to
                                                                     Lake Biology and the Limnoplankton." Wiley, New York. 1,115 pp.
                                                          JÄRNEFELT, H. 1956: Zur Limnologie einiger Gewässer Finnlands. XVI. Mit
                                                                     besonderer Berücksichtigung des Planktons. Suomal. eläin-ja kasvit.
                                                                     Seur. van. Julk. 17 (1). 201 pp.
                                                          JOLLY, V. 1959: A limnological study of some New Zealand lakes. (Ph.D. thesis
                                                                     lodged in University of Otago library.)
                                                          LUND, J. W. G. 1949: Studies on Asterionella. 1. The origin and nature of the
                                                                     cells producing seasonal maxima. J. Ecol. 37: 389-419.
                                                                   1954: The seasonal cycle of the plankton diatom, Melosira italica (Ehr.)
                                                                     Kütz. subsp. subarctica O. Müll. Ibid. 42: 151-79.
                                                                 —1955: Further observations on the seasonal cycle of Melosira italica
                                                                      (Ehr.) Kütz. subsp. subarctica O. Müll. Ibid. 43: 90-102.
                                                          MATTHEWS, L. J. 1967: Further results of spraying lake weeds. In Chapman,
                                                                     V. J. and Bell, C. A. (Eds.), "Rotorua and Waikato Water Weeds:
                                                                     Problems and the Search for a Solution", pp. 40-4. Department of
                                                                     University Extension, the University of Auckland, Auckland.
120        N.Z.    JOURNAL OF MARINE & FRESHWATER RESEARCH                              [MAR.

                                                          NAUMANN, E. 1931: Limnologische Terminologie. In Abderhalden, E. (Ed.),
                                                                    "Handbuch der Biologischen Arbeitsmethoden". Abt. IX, Teil 8.
                                                                    Urban and Schwarzenberg, Berlin and Vienna. 776 pp.
                                                          RAWSON, D. S. 1956: Algal indicators of tropliic lake types. Limnol. Oceanogr. 1:
                                                          REID, J. 1964: Study of cause and effects of eutrophication. in Lake Rotorua.
                                                                    Health Department Rep., Rotorua.
                                                          THOMASSON, K. 1960: Some planktonic Staurastra from New Zealand. Bot.
                                                                    Notiser 113: 225-45.
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                                                                                              APPENDIX I

                                                                           Numbers of plant and animal species in each sample

                                                                                                         Open lake station
                                                                      Kawaha                                                                Mokoia
                                                                       Point                                                                Island
                                                                                               Bottom              9m            Surface

                                                                                                     a!                                a
1969]        CASSIE—SEASONAL VARIATION IN PHYTOPLANKTON                            121

                                                                                             APPENDIX    II

                                                                                             SPECIES L I S T

                                                                  (Key to localities: l=Lake Rotorua, 2=Lake Rotoiti, 3=Lake Ohakuri.)
                                                                Anacystis cyanea Drouet and Daily                                    1,2,3
                                                                Chroococcus sp.                                                      1,2
                                                                Dactylococcopsis smithii Chodat and Chodat                           1,2
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                                                                Agmenellum quadruplicatum Breb.                                      1
                                                                Anabaena flos-aquae (Lyng.) Breb.                                    2
                                                                Anabaena circinalis Rabenh.                                          1,2,3
                                                                Lyngbya birgei G. M. Smith                                           1
                                                                Lyngbya hieronymusii Lemm.                                           1,3
                                                                Merismopedia elegans var. major G. M. Smith                          1
                                                                Nodularia spumigena Mertens                                          1
                                                                Oscillatoria sp.                                                     1,2,3

                                                                Eudorina elegans Ehr. ...                                            1,2,3
                                                                Pandorina morum (Mull.) Bory
                                                                Volvox sp.                                                           3
                                                                 Geminella minor (Nag.) Heering                                      3
                                                                 Ulothrix sp.                                                        1,2
                                                                Actinastrum hantzschii Lagerh.                                       1,3
                                                                Ankistrodesmus sp.                                                   1,2
                                                                Botryococcus braunii Kiitz.                                          1,2,3
                                                                Botryococcus protuberans West and West                               3
                                                                Coelastrum sphaericum Nag.                                           1,2,3
                                                                Dictyosphaerium ehrenbergianum Nag.                                  1,3
                                                                Dictyosphaerium pulchellum Wood                                      1,2,3
                                                                Ererella bornhemiensis Conrad
                                                                Micractinium pusillum Fresen.                                        3
                                                                Nephrocytium agardhianum Nag.                                        2
                                                                Oocystis pusilla Hansg.                                              3
                                                                Pediastrum duplex var. gracillimum West and West.....                1,3
                                                                Scenedesmus quadricauda (Turp.) Breb.                                1
                                                                Selenastrum gracile Reinsch                                          3
                                                                Tetraedron regulare var. granulare Prescott                          2,3
                                                                Actinotaenium pyramidatum (W. and W.) Teiling
                                                                Closterium aciculare T. West                                             ,2,3
                                                                Closterium cornu Ehr.                                                    ,
                                                                Closterium setaceum Ehr.                                                  3
                                                                Cosmarium contractum var. ellipsoideum (Elfv.) G. S. West                ,2
                                                                Echinosphaerella limnetica G. M. Smith
                                                                Micrasterias sp.                                                       ,2
                                                                Mougeotia sp.                                                        1,2,3
                                                                Sphaerozosma aubertianum W. West                                     2
122        N.Z.   JOURNAL OF MARINE & FRESHWATER RESEARCH                  [MAR.

                                                                Spinocosmarium sp.      ..         ..      ..    ..      ..              ..1,2
                                                                Spondylosium planum (Wolle) West and West        ..      ..              ..1,2
                                                                Staurastrum anatinum f. longibrachiatum (W. and W.) Brock. .             . . 1,2
                                                                Staurastrum leptocladum var. elegans G. S. West ..         ..              ..1,2
                                                                Staurastrum longiradiatum f. majus West and West ..       ..                 3
                                                                Staurastrum muticum Breb.         ..      ..    ..      ..              ..1,2
                                                                Staurastrum smithii (G. M. Smith) Teiling..     ..      ..              ..1,3
                                                                Staurodesmus leptodermus (Lund) Teiling ..      ..      ..              ..1,2
                                                                Staurodesmus triangularis (Lagerh.) Teiling      ..      ..               ..1,2
                                                                Staurodesmus dickiei (Ralfs) Lillier      ..    ..      ..             .. 2
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                                                                 Ceratium hirundinella f. furcoides Schrod. ..        ..      ..        .. 1
                                                                 Glenodinium sp.           ..       ..      ..        ..      ..        .. 2
                                                                 Peridinium striolatum Playf.     ..       ..        ..      ..         ..1,2
                                                                Cystodinium cornifax (Schillg.) Klebs        ..      ..      ..        ..    1,2,3
                                                                Synura uvellaEhr.       ..         ..        ..      ..      ..         ..1,2,3
                                                               Dinobryon cylindricum var. alpinum (Imh.) Bachm. ..            ..        .. 1,2, 3
                                                               Dinobryon sertularia Ehr.       ..       ..     ..            ..        .. 1,2, 3
                                                                 Cyclotella stelligera Cleve and Grun.    ..         ..      ..        .. 2
                                                                 Melosira distans (Ehr.) Kiitz.    ..     ..         ..      ..         ..1,2
                                                                 Melosira granulata Ralfs          ..     ..         ..      ..        . . 1, 2, 3
                                                                 Melosira granulata var. angustissima O. Mull.       ..      ..         ..1,2,3
                                                                 Melosira islandica subsp. helvetica O. Mull.         ..      ..         .. 1
                                                                 Melosira undulata (Ehr.) Kiitz. ..       ..         ..      ..        .. 3
                                                                 Rhizosolenia eriensis H. L. Sm. ..       ..         ..      ..         ..1,2
                                                                 Stephanodiscus sp.        ..       ..     ..         ..      ..         .. 1
                                                                Amphora sp. ..          ..      ..           ..      ..      ..          ..1,2
                                                                Asterionella formosa Hass.       ..           ..      ..      ..          ..1,2,3
                                                                Fragilaria capucina Desmaz.        ..           ..      ..      ..        .. 1,2,3
                                                                Fragilaria sp. ..        ..      ..           ..      ..      ..         .. 3
                                                                Gomphonema sp.           ..      ..           ..      ..      ..         .. 1, 2, 3
                                                                Surirella ovalis Breb. ..       ..           ..      ..      ..        .. 3
                                                                Surirella turgida W. Sm.        ..           ..      ..      ..          ..1,2
                                                                Synedra acus Kiitz.     ..      ..           ..      ..      ..          ..1,2
                                                                Synedra ulna (Nitzsch) Ehr.     ..           ..      ..      ..        . . 1,2, 3
                                                                 Tabellariaflocculosa(Roth) Kiitz.            ..      ..      ..         .. 1
                                                                Euglena (4 spp.)        ..         ..        ..      ..      ..        .. 1
                                                                Phacus sp.     ..       ..         ..        ..      ..      ..        .. 2
                                                                Pyxidium sp. . .        ..         ..        ..      ..      ..        .. 1
                                                                Vorticella sp. . .       ..         ..        ..      ..      ..        .. 1
1969]        CASSIE—SEASONAL VARIATION IN PHYTOPLANKTON                     123

                                                                  Asplanchna sp.          ..        ..     ..    ..    ..     ..1,3
                                                                  Filinia major Colditz . .         ..     ..    ..    ..    .. 1
                                                                  Keratella cochlearis (Gosse)       ..     ..    ..    ..    . . 1,2,3
                                                                  Trichocerca longiseta (Schrank)    ..     ..    ..    ..    .. 1
                                                                  Calamoecia lucasi Brady         ..     ..      ..    ..    ..   1
                                                                  Bosmina meridionalis Sars       ..     ..      ..     ..    ..1,3
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