Reproductive cycle and cohort formation of Venus antiqua (Bivalvia: Veneridae) in the intertidal zone of southern Chile
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Revista Chilena de Historia Natural
70: 181-190, 1997
Reproductive cycle and cohort formation
of Venus antiqua (Bivalvia: Veneridae)
in the intertidal zone of southern Chile
Ciclo reproductivo y formaci6n de una cohorte de Venus antiqua
(Bivalvia: Veneridae) en el intermareal del sur de Chile
ROBERT A. STEAD 1, ELENA CLASING 2 ,
JORGE M. NAY ARR0 3 and GLADYS ASENCI0 4
Instituto de Biologfa Marina. Universidad Austral de Chile, Casilla 567, Valdivia, Chile
1
Present address: Biology Department. Memorial University of Newfoundland, St. John's, Newfoundland A IB3X9, Canada
E-mail: stead@morgan.ucs.mun.ca, 2eclasing@valdivia.uca.uach.cl,
3jnavarro@ valdi via. uca.uach.cl, 4 gasencio@ valdi via. uca.uach.cl
ABSTRACT
The reproductive cycle and generation of a new cohort of the clam Venus antiqua is described in relation to the annual food
availability and temperature cycle at Yaldad Bay, Chiloe Island, southern Chile. The spawning period followed a seasonal
pattern and was restricted to spring and summer (November 1990 to February 1991 ). whereas during autumn and winter the
population was reproductively quiescent. First settlers were detected in January 1991, approximately thirty days after the
main spawning event. Mean shell length at settlement was 0.26 mm; growth rate of this cohort was rapid till the end of
summer (0.0021 to 0.0085 mm·d- 1). reaching an average length of I mm at the end of March, whereas during autumn and
winter (May to September) almost no shell growth was observed. The cohort recommenced growth in spring 1991 (Octo-
ber) and the clams quickly attained an average length of 6 mm (0.0248 to 0.0510 mm·d- 1) at the end of the first year
(January 1992). Both the reproductive cycle and growth of this cohort at Yaldad Bay followed a seasonal pattern which was
coupled to water temperature and food supply (chlorophyll a and organic seston).
Key words: Reproductive cycle, cohort formation, Bivalvia.
RESUMEN
Se describe e1 ciclo reproductivo y la generacion de una cohorte de Venus antiqua en relacion a la oferta alimentaria anual
y al ciclo de temperatura en la Bahfa Yaldad, Isla de Chiloe. sur de Chile. El periodo de desove en adultos siguio un patron
estacional, restringiendose al periodo de prima vera y verano (noviembre 1990 a febrero 1991 ), permaneciendo la poblacion
en estado de minima actividad durante el otoiio e invierno. Los primeros individuos asentados se detectaron en enero 1991,
aproximadamente treinta dfas despues de ocurrido el principal evento de desove. El asentamiento ocurrio a una talla media
de 0,26 mm; la cohorte crecio rapidamente hasta fines de verano (0,0021 a 0,0085 mm·d- 1) alcanzando a fines de marzo una
talla promedio de 1 mm, mientras que practicamente no se observo crecimiento durante el otoiio e invierno (mayo a
septiembre). El crecimiento de Ios individuos de la cohorte se reanudo en primavera (octubre 1991) alcanzando rápida-
mente una talla promedio de 6 mm (0,0248 a 0,0510 mm·d- 1) al final del primer aiio de vida (enero 1992). Tanto el ciclo
reproductivo como el crecimiento de la cohorte siguio un patron estacional fuertemente ligado al ciclo de temperatura del
agua y a la oferta alimentaria (clorofila ay seston organico) en Bahfa Yaldad.
Palabras clave: Ciclo reproductivo, formacion de cohorte, Bivalvia.
velopment and growth (Newell et al. 1982).
INTRODUCTION Each species has a variety of genetic and
environmental adaptations which coordi-
Marine bi valves from temperate latitudes nate these reproductive events with the
generally follow a cyclical pattern of repro- environment in order to maximize repro-
duction which can be divided into three ductive success (Newell et al. 1982). The
stages: gametogenesis and vitellogenesis, duration of each one of these stages can be
spawning and fertilization, and larval de- annual, semi-annual or continuous, depend-
(Received 19 October 1995; accepted 20 June 1997; managed by F. Patricio Ojeda)182 STEAD ET AL.
ing on the particular species and the tion and growth of post-larvae in the field
environmental influences. Environmental will contribute towards improved stock
factors will affect the number of cohorts management and mariculture practice.
produced annually as well as their subse- The present study analyzes the reproduc-
quent growth and survivorship. tive cycle of Venus antiqua and its relation-
Whilst studies relating to the reproduc- ship with several important environmental
tive cycle and growth of bivalve species variables in the generation of a new cohort
from the northern hemisphere are numerous in the natural habiatat of this species.
(Ansell 1961, Ansell et al. 1964a, I 964b,
Kautsky I 982a, 1982b, MacDonald &
Thompson 1985a, 1985b, Harvey & Vincent MATERIAL AND METHODS
1989, 1990), few studies for the Chilean
coast have integrated both these aspects with The study was carried out on the tidal flat
environmental variables. Such is the case of at Yaldad Bay, Chiloe Island, southern
the infaunal filter-feeding bivalve Venus an- Chile (43° OS'S; 73 44'W) (Fig. 1). The
tiqua King & Broderip 1835, which inhabits tidal flat (0.5 % slope) is exposed over a
intertidal and shallow sandy bottoms along distance of 500 m during EL WS (semi-di-
the Pacific coast of South America from urnal tides). The Venus antiqua bank is re-
about 12° S to 54° S and along the Atlantic stricted to the lower half of the intertidal
coast south of 31° S, including the Falkland zone, which is constituted of gravelly mud-
Islands (Osorio et al. 1983). Individuals are dy sand containing 2.4 % of combustibles
iteroparous and follow an indirect reproduc- (i.e., organic matter) with a mean grain size
tive strategy; size at first reproduction (46- of 0.5 mm. Specimens were collected ran-
48 mm length, Lozada & Bustos 1984) is domly by hand at monthly intervals from
attained at an age of 4 to 5 years, whereas the study area at ML WS, between Septem-
commercial harvesting begins when clams ber 1990 and November I 99 I (except Apri I
reach 55 mm (5-6 years of age) (Clasing et I 991); I 0 male and I 0 female clams within
al. 1994). Despite the wide distribution of V. a shell length range of 50 to 55 mm were
antiqua and its significance to artisanal fish- immediately selected for histological analy-
eries, only a few investigations on its biolo- sis. The gonads were preserved in aqueous
gy and ecology have been carried out (see Bouin's fixative and later embedded in par-
Jerez et al. 1991 ). affin wax. Tissue was cut in 7 f..Lm sections
The large tidal amplitude (6.85 m max- and stained with hematoxilyn and eosin.
imum) found in the Chiloe Archipelago Gonadal tissue sections were qualitatively
(Chile) has enhanced the formation of ex- examined and classified into one of four
tensive tidal flats, which are characterized maturity stages (developing, ripe, spawn-
by their high biological productivity (Viv- ing, post-spawning) according to the de-
iani I 979). In terms of biomass, the infau- scription of Lozada & Bustos (1984).
nal bivalve Venus antiqua is one of the Growth of the individuals within a co-
dominant species in this environment. On hort was monitored by sampling the clams
the tidal flat of Yaldad Bay, the species is present in the upper 0.5 cm of the sediment.
restricted to the lower half of the intertidal Sediment samples taken at monthly inter-
zone, where in past years it has reached vals (September I 990 to February I 992)
average densities of 270 ind.-m- 2 (R. each consisted of 25 subsamples obtained
Stead, personal observation). However, with a 2. I cm diameter plastic corer tube
this bank was heavily exploited shortly af- introduced to a depth of 0.5 cm, i.e., a total
ter the start of this investigation, consider- sampled area of 85 cm 2 . The sediment re-
ably reducing the abundance of individu- tained on a I 25 f..Lm mesh sieve was exam-
als to less than 50 ind.-m- 2 • Due to the ined under a dissecting microscope. Indi-
currently overexploited status of this re- viduals identified as Venus antiqua were
source in Chile (Re yes et al. 199 I, Clasing measured (maximum shell length) with a
et al. 1994 ), a more thorough understand- calibrated ocular graticule to an accuracy
ing of reproductive timing and the forma- of 0.015 mm. Average shell length was ea!-REPRODUCTIVE CYCLE AND COHORT FORMATION OF VENUS ANTIQUA 183
N
~
Intertidal zone
0 300m
73°44'
Fig. 1: Location of the study site at Yaldad Bay, Chiloe island, Chile.
Localizaci6n del sitio de estudio en Bahia Yaldad, Isla de Chiloe, Chile.
cu1ated from all individuals collected on zooplankton and debris, before filtering
each sampling occasion, whereas growth through prewashed, precombusted, pre-
rate of the cohort was estimated by obtain- weighed Whatman GF/C filters. The ob-
ing the difference in average shell length tained samples were stored in darkness at
between two consecutive samplings (L1L= -20 °C until analysis.
Lr L 1) and dividing by the number of days
between them (L1t = t 1 - t 2).
Salinity and water temperature were RESULTS
monitored on each sampling occasion using
a WTW LF 191 conductivity meter and a Reproductive cycle
0.1 °C precision thermometer, respectively.
In order to determine the seasonal vari- Histological analysis revealed slightly dif-
ability of food avai !able for reproduction ferent reproductive patterns for male and
and growth, seston and pigment quantifica- female clams (Fig. 2). Only one important
tion (chlorophyll a and phaeopigments) reproductive period (i.e., over 50 % of the
were estimated using the techniques de- population in the spawning stage) was ob-
scribed by Strickland & Parsons (1972). served throughout the year. In both sexes
Water samples (1-2 I) obtained every hour spawning was restricted to spring and sum-
throughout one tidal cycle (6 hours) were mer, with the highest frequencies of spawn-
pumped from a distance of I 0 cm above the ing individuals (93 % females, 83 % males)
clam bed and then filtered through a 333 occurring in December 1990. The repro-
f.Lm nitex mesh sieve to eliminate larger ductive period (i.e., spawning) in females184 STEAD ET AL.
extended the spawning phase until mid-au-
·,~~~
1001 developing
80
.// 0 I tumn (May 1991 ). Spawning in both sexes
was followed by a period of reproductive
, "\\ I quiescence, which was prolonged in fe-
60 males (approximately 6 months; February
0
/ 1\ I
to July) compared to males (3 months; June
201
40 .~~~\\
0
. /_.'_'...·
0 0 b~
\\
II
to August). Gonad maturation restarted in
late winter - early spring (August-Septem-
ber 1991) in most of the adult population,
0+-l ~~........... • ' '.
and by October a large proportion of indi-
viduals were ripe. By November 1991, 90
100 ripe
% of the population was in the spawning
stage, I month earlier than, but following a
pattern similar to the previous year.
60
·------
~
..__., Settlement and growth
40
>,
0 20 The first post-settled individuals were col-
c lected on 16 January 1991, when shell
0
Q)
lengths ranged between 330 and 665 IJ.m.
::J
Measurement of the prodissoconch 11 ring of
.1\
o-
100 spawning specimens < 500 IJ.m long (n= 34) showed
•
Q)
1....
80 that settlement had occurred at an average
LL
size of 264 IJ.m (1 S.D. = ±12.8 IJ.m). The
/0 0
60 cohort grew rapidly until the end of summer
40
0\o (2.09 to 8.55 IJ.m·d- 1, January- March 1991),
whereas during autumn and winter (May-
20 / •.i .\ August) a very low growth rate was ob-
0
• '
···&0-·~·~~--4·-rl·....... , • •
\~ I-e-......o"'•~i~..---l
• ·-· j
served (Table 1). In spring, individuals re-
_·.-rl·
••
commenced growth and attained an average
size of 6 mm after the first year's lifespan
100 post- spawning (January 1992) (Table I).
80
Temperature and salinity
J\/~
60
Water temperature showed a seasonal pattern,
40
the lowest values occurring during the winter
20 ~ months (9.8 C in July 1991) and increasing
I. ""' \ I \ /.
ef •
0
towards summer (17 C in January 1992). Sa-
0 ...... lil • • .,.......& ......, ..
linity was stable throughout the present
ONDJFMAMJJASON
1990 1991 study, fluctuating around 28 (Fig. 3 A).
• - • Female o ·········o Male
Seston
Fig. 2: Gametogenic phases of female and male
Venus antiqua. The values represent the percen-
tage frequency of clams in each reproductive
Organic and inorganic seston followed a
phase (100% = 10 specimens). pattern similar to that of temperature dur-
ing most of the study period. Highest val-
Estados gametogenicos de hembras y machos de Venus anti-
qua. Los valores representan el porcentaje de frecuencia de ues (48 mg·I- 1, total seston) were observed
individuos en cada estado reproductive (100% = 10 individuos) at the end of spring 1990 (November-De-
cember), and were most probably due to
lasted until mid-summer (January 1991); the effect of resuspension of bottom de-
males followed a similar pattern until Janu- posits observed during strong prevailing
ary, but quickly recovered in February and winds from the north. The rest of the studyREPRODUCTIVE CYCLE AND COHORT FORMATION OF VENUS ANTIQUA 185
Table I
Mean shell length (~-tm) and mean growth rate (~-tm d- 1)
of Venus antiqua spat settled between January and March 1991 at Yaldad Bay.
Talla media (flm) y tasa de crecimiento promedio (flm d· 1)
de postlarvas de Venus antiqua asentadas entre enero y marzo de 1991 en Bahfa Yaldad.
sampling length [flm] n growth rate
date x ±(I S.D.) (flm. d·l)
1990
16 January 463.54 (74.46) 50
3 March 865.17 (162.43) 178 8.5453
29 March 919.93 (162.43) 159 2.0946
15 May 975.00 (150.14) 19 1.1717
14 June 997.63 (188.63) 19 0.7543
16 July 1040.87 (40.00) 5 1.3513
10 August 1060.55 (42.50) 6 0.7872
10 September 1097.50 (95.46) 4 1.1919
11 October 1865.23 (23.46) 8 24.7581
23 November 3684.00 (700.00) 50 42.3023
20 December 4476.00 (800.00) 87 29.3333
1991
20 January 6058.00 (I 037.00) 99 51.0323
19 February 7158.00 (1565.00) 67 36.6667
period was characterized by a low organic DISCUSSION
and inorganic seston concentration with
values below 4 mg·l- 1 and 8 mg·l- 1 respec- Reproductive cycle
tively (Fig. 3 B).
The reproductive cycle of Venus antiqua at
Pigments Yaldad Bay is the first to be described for
an intertidal population of this species in
Chlorophyll a reached a maximum con- Chile. There was a single reproductive pe-
centration during late spring 1990 (No- riod which extended from November 1990
vember-December) and summer 1991- to the end of February 1991 (Fig. 2, spawn-
1992 (February) following a seasonal ing). These results are broadly comparable
cycle similar to that found for seston and with those reported by Lozada & Bustos
temperature. The main peak observed dur- ( 1984) who observed at An cud Bay, Chile
ing spring 1990 was greater (40 jlg·l- 1) and one important spawning period during De-
more prolonged than the main peak for cember and January followed by two minor
summer 1991-1992 (22 jlg·l-1) (Fig. 3 C) events (< 1 month) in April and August re-
although the magnitude of the former can spectively (Fig. 4 A). Weber (1992), ob-
be partly attributed to the effect of bottom served that Venus antiqua from Metri, Seno
resuspension. Fluctuation of phaeopigment de Reloncavf, spawned on two occasions
concentration was similar to that of chlo- during the year: at the end of summer (Feb-
rophyll a, with highest values occurring ruary to March 1991) and at the end of win-
during spring 1990 (November-December) ter to the beginning of spring (mid August
as a consequence of the resuspension of bot- to mid October 1991) (Fig. 4 B). However,
tom detritus. Phaeo-pigment values both these studies were carried out on sub-
throughout the rest of the year were rela- tidal populations, where environmental fac-
tively low (Fig.3 C). tors tend to be more stable, especially with186 STEAD ET AL.
35~------------------------------------------------~ 25
........ 30 ****
AO····-o·····o·····O·········-·o .O·····o----0·-----·-·--o·····O. *** ..o····O--... o -i
0 .... ·o·
·o·····
CD
0
......... 25 20 3
0 1J
20 .,
./·"""·-·
CD
15
./·-............. ·-· .............
15 Q
c
0
(/)
10
5
____.............
- · - · - · o ··--··o ---
./
•-- •
Salinity
Temperature
10
..,c
CD
........
(')
0
0+-.--.-.-,.-.-,--.-.-.--.-.-,.-.-.--.-~.-~-+ 5 .._,
·--·
35~--------------------------------------------~
8
;:. .
~
30 **** Inorganic
~:
I A····· A Organic
0>
E
15
I
c ,' ·.
.
0 :' \
10 .· ·.
C> 5 • __ A.,.· \ ..•......._ /•-•"" *** •
(/)
Q +-----,A,_--,-,---,-~---·-·.,·:_~_··~-~~~-----~r·-··_··TA·_··-··,6_··_··~-:!:.:~.:.:-·.:.:··,:_··_··_;_·::;:_-.__··_:_··:;_!·_··_··_:;:t:_-::--_
..,.._.._.._.:;:._)>_
- :J
Ill
30
c: 20
0..
E
C>
0> 10
_•....,.....11REPRODUCTIVE CYCLE AND COHORT FORMATION OF VENUS ANTIQUA 187
100
80
A o - o Male & Female
,--....
60
~
............
40
>-
20
()
c 0
Q.)
100
B
:::J
e:.--e:. Male
0"" 80 • ----- • Female
Q.)
60
!......
lL
40
20
0
0 N D j F M A M j j A s 0 N
Fig. 4: Frequency of spawning adult Venus antiqua clams reported for: (A) Ancud Bay, Chiloe
Island, Chile (Adapted from Lozada & Bustos 1984), (B) Metri, Seno de Reloncavf, Chile (Adapted
from Weber 1992).
Frecuencia de adultos de Venus antiqua en desove reportado para: (A) Bahfa Ancud, Isla de Chiloe, Chile (Adaptado de
Lozada & Bustos 1984), (B) Metri, Seno de Reloncavf, Chile (Adaptado de Weber 1992).
occurs only under environmentally favor- vironment (sensu Newell et al. 1982).
able conditions. Akberali & Trueman However, the prolonged spawning period
(1985) pointed out that intertidal bivalves observed in male clams (approximately 6
are periodically confronted with stressful months, 2 events) indicates that they
conditions, which results in prolonged quickly recover after spawning. The oc-
valve closure. During these unfavorable pe- currence of a second spawning event (al-
riods bivalves cease to feed, reproduce and though probably of less importance than
grow (Bayne & Newell 1983, Akberali & the first), is similar to the pattern de-
Trueman 1985, Wilson & Elkaim 1991 ). scribed by Lozada & Bustos (1984) and
The Venus antiqua population studied Weber ( 1992) for other subtidal popula-
is comparable with other intertidal bivalve tions of V. antiqua. This suggests that
populations (Seed & Brown 1977, Feder et male clams are perhaps less affected by
al. I 979, Harvey & Vincent I 989) in that tidal exposure than females and may re-
reproductive output is limited to one sin- quire less energy for the production of ga-
gle time of the year; in contrast to subtidal metes. However from an ecological point
populations of the same species in which of view, the extended spawning behaviour
reproduction is more continuous, suggest- of male clams is of little value unless it
ing an adaptive strategy to this type of en- occurs in response to subtidal Venus anti-188 STEAD ET AL.
qua females with similar prolonged thors have suggested that only food supply
spawning periods. Prolonged spawning of is important in controlling these processes
males only, has also been observed in an (Bayne & Newell 1983, Brey & Hain
intertidal population of the venerid clam 1992), spawning of V. antiqua at Yaldad
Protothaca staminea (Feder et al. 1979). Bay started during both years at similar wa-
ter temperatures (12.4 °C and 12.5 °C, in
Settlement and growth 1990 and 1991 respectively), suggesting a
strong influence of temperature on repro-
The main spawning period (December duction. According to Mackie (1984), the
1990), was followed after approximately 30 maturation of gametes is induced either by
days by the beginning of the settlement the annual temperature fluctuations or a thresh-
period (Table 1), which extended from J an- old temperature, whereas the act of spawn-
uary to March 1991 (R. Stead, unpublished ing is initiated when temperatures exceed a
data). These results coincide with laborato- critical level characteristic for each species
ry experiments where larvae took between (e.g., 10-12 °C in Mytilus edulis), but again
23 and 28 days to settle (R. Stead, unpub- the characteristics can vary from one local-
lished data). The new cohort exhibited ity to another and depend also on the nutri-
maximum growth rates from the moment of tive value of food available (Seed &
settlement until the beginning of March, by Suchanek 1992). On the other hand, growth
which time clams were five times larger of Venus antiqua spat can be maintained
than at the time of their settlement (Table during periods of low natural food supply
1). A period of slower growth during au- (autumn and winter) by adding cultured mi-
tumn and winter is then followed by rapid croalgae, despite the decrease in water tem-
growth during spring (Table 1). The same perature (P. Katz, personal communica-
growth pattern was observed by Clasing et tion), emphasizing the important role of
al. ( 1994) in Venus antiqua juveniles (> 2 food supply on the growth of this species.
years old) and adult clams from Yaldad Our results demonstrate that young clams
Bay. The seasonal growth and reproductive are faced with low natural food supply upon
cyclical pattern are strongly related to the recruitment, largely limiting growth to their
seasonality of water temperature, particu- first three months of life and therefore mak-
late organic matter (POM) and clorophyll a ing them more vulnerable to predation (sen-
concentration, although low chlorophyll a su Kraeuter & Castagna 1989). For aquacul-
and POM concentration at the end of the ture or repopulation of overexploited areas
study (October - November 1991) are in- like Yaldad Bay, the artificial production of
consistent with this interpretation. Howev- "seedlings", at the end of winter, followed
er, Navarro et al. (1993) concluded that by their transfer to the natural environment
chlorophyll a peaks in November- Decem- at the beginning of spring, would enable
ber 1990 and February 1992 at Yaldad Bay these individuals to take advantage of the
(Fig. 3 C) were produced by high diatom greater food supply during spring and sum-
concentrations (30·1 0 6 cells-1· 1), whereas mer, thus allowing them to grow to a larger
microflagellate blooms (21·1 0 6 cells·l- 1) in size (with possibly better survival rates) be-
July and November 1991 were not reflected fore encountering unfavorable winter condi-
in high clorophyl a values; high mi- tions. This strategy would also reduce the
croflagellate concentrations may therefore interval before the onset of commercial har-
explain growth and gonad development vesting, which starts when clams reach 55
during the second year (October and No- mm in shell length.
vember 1991).
The influence of temperature and food
on growth and reproduction in bivalves is ACKNOWLEDGMENTS
well documented (e.g., Bayne & Worrall
1980, MacDonald & Thompson 1985a, We sincerely thank E. Jaramillo, R.
1985b, Harvey & Vincent 1989, Jaramillo Jaramillo and C. Moreno, all from Univer-
& Navarro 1995) and although some au- sidad Austral de Chile, whose critical corn-REPRODUCTIVE CYCLE AND COHORT FORMATION OF VENUS ANTIQUA 189
ments improved an earlier version of this Experimental Marine Biology and Ecology 177:
171-186
manuscript. This manuscript was also bene- EM MET B, K THOMPSON & JD PO PH AM ( 1987) The
fited from comments made by M. Harvey reproductive and energy storage cycles of two
(Universite Lava!, Canada), C. Richardson populations of Mytilus edulis (Linne) from British
Columbia. Journal of Shellfish Research 6: 29-36.
(University of Wales) and R. Thompson FEDER HM, JC HENDEE, P HOLMES, G MUELLER &
(Memorial University of Newfoundland). AJ PAUL (1979) Examination of a reproductive
We are greatly indebted to the Instituto de cycle of Protothaca staminea using histology, wet
weight-dry weight ratios, and condition indices.
Embriologfa (Universidad Austral de Veliger22: 182-187.
Chile) for the use of laboratory facilities HARVEY M & B VINCENT (1989) Spatial and temporal
for histological processing. Thanks are also variations of the reproductive cycle and energy
allocation of the bivalve Macoma balthica (L.) on a
due to GTZ (Germany) for the donation of tidal flat. Journal of Experimental Marine Biology
a Zeiss-Axioskoop Microscope used here. and Ecology 129: 199-217.
This work was supported by FONDECYT HARVEY M & B VINCENT (1990) Density, size
distribution, energy allocation and seasonal
Grant No. 90-0306. variations in shell and soft tissue growth at two
tidal levels of Macoma balthica (L.) populations.
Journal of Experimental Marine Biology and
Ecology 142: 151-168.
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