REEF SNAPSHOT SUMMER 2020-21
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REEF SNAPSHOT SUMMER 2020-21
© Commonwealth of Australia, 2021, published by the Great Barrier Reef Marine Park Authority
ISBN 978 0 6450437 0 9
The Reef snapshot: summer 2020-21 is licensed by the Commonwealth of Australia for use under a Creative Commons By
Attribution 4.0 International licence with the exception of the Coat of Arms of the Commonwealth of Australia, the logo of the
Great Barrier Reef Marine Park Authority, the Australian Institute of Marine Science and CSIRO, any other material protected by a
trademark, content supplied by third parties and any photographs. For licence conditions see: http://creativecommons.org/licences/
by/4.0
This publication should be cited as:
Great Barrier Reef Marine Park Authority, Australian Institute of Marine Science, and CSIRO 2021, Reef snapshot: summer 2020-21,
GBRMPA, Townsville.
Cover image: © Great Barrier Reef Marine Park Authority 2018. Inside images: Page 1 extract from the artwork ‘Step of Change’ by
Juru Traditional Owner Nicky Bidju Pryor (© Bidju Designs 2018); Page 2 © Victor Huertas 2020; Page 6 © Frederieke Kroon 2016, ©
CSIRO 2018, © Matt Curnock 2020.
This snapshot draws on various types of information, including:
Climate time series data (www.bom.gov.au/climate/change)
Cyclone wave damage predictions (www.nature.com/articles/srep26009)
eReefs GBR4 rivers 2.0 model data (http://dapds00.nci.org.au/thredds/catalogs/fx3/catalog.html?dataset=gbr4_2.0_rivers)
Eye on the Reef program data (www.gbrmpa.gov.au/our-work/eye-on-the-reef)
Long-term Monitoring Program survey reports (www.aims.gov.au/docs/research/monitoring/reef/latest-surveys.html)
ReefTemp data (www.bom.gov.au/environment/activities/reeftemp/reeftemp.shtml)
We acknowledge the continuing sea country management
and custodianship of the Great Barrier Reef by Aboriginal
and Torres Strait Islander Traditional Owners, whose rich
cultures, heritage values, enduring connections and shared
efforts protect the Reef for future generations.
1
About this snapshot
AUSTRALIA
Summer is a critical time for the health of coral. This snapshot Summary for 2020-21
provides a summary of the conditions on the Great Barrier
Reef this summer, what this means for coral, and what actions • Conditions were relatively good for coral recovery.
are underway. The focus is coral, it does not examine the • There were no prolonged high temperature or major
health of other habitats or species, however, these may be cyclone disturbances, and many reefs continued their
added for future snapshots. recovery from past impacts.
Each year, towards the end of summer, the snapshot is • Water temperatures did not cause as much coral heat
prepared by the three main Australian Government agencies stress as recent years, although all months were warmer
responsible for Reef management and science: the Great than average.
Barrier Marine Park Authority, Australian Institute of Marine • Cyclone Kimi was the only tropical cyclone that tracked
Science (AIMS), and CSIRO. across the Reef, and its potential to cause widespread
catastrophic damage to reefs was assessed as very low.
This snapshot is based on the latest available information • While there was some good rainfall in the catchment,
at the time of writing. It does not take the place of ongoing flood levels in waterways near the Reef were generally not
rigorous reporting by all agencies. It sets the scene for the major or sustained.
more comprehensive reports released later in the year, such • Crown-of-thorns starfish remain at outbreak or potential
as the mid-year Long‑term Monitoring Program reports outbreak levels in parts of the northern, central and
by AIMS and reports from the Marine Monitoring Program (particularly) southern regions of the Reef. The Crown-of-
managed by the Marine Park Authority. thorns Starfish Control Program continues to work in all
three regions to cull starfish down to non-outbreak levels.
Coral
monitoring
programs
AIMS has been monitoring the length and breadth of
the Great Barrier Reef for more than 35 years.
The Long-term Monitoring Program is the most
comprehensive record of coral reef condition
available for the Reef with a focus on the long-term
trends in coral decline and recovery. Ninety‑three
reefs are routinely monitored as part of this program.
An additional 32 inshore reefs are monitored as part
of the Marine Monitoring Program managed by the
Marine Park Authority.
Additional observations are gathered by the
multiple organisations and people contributing to
the Eye on the Reef program, including through the
Reef Joint Field Management Program.
2
This summer, conditions were relatively good for coral recovery.
What has Just like any natural system, the Reef goes through cycles of
disturbance and recovery. It is also very large, and disturbances
affect it at a range of local and regional scales. This means Reef
the Reef
condition can be variable across different locations.
Climate change is the greatest threat to the Reef. It influences
weather patterns and the ocean’s temperature, pH level and currents,
experienced?
as well as intensifying the effects of other threats. Climate change is
escalating, and the Reef is already experiencing the consequences of
this.
Unfortunately, the events that cause disturbances on the Reef are
becoming more frequent, leaving less time for coral recovery.
Four key stresses on coral reefs:
• Above average sea temperatures: an increase of only one degree Celsius above normal summer maximum sea temperature
for just four weeks can trigger coral bleaching and potentially death. The level of bleaching risk is assessed by the number of
Degree Heating Days, a measure of the accumulation of heat stress over a period of time.
• Cyclones and storms: powerful waves generated during cyclones can seriously damage habitat, particularly coral reefs.
• Flood plumes: when large volumes of fresh, muddy water flow from the catchment into the ocean after intense or prolonged
rainfall, it is called a flood plume. Intense or prolonged rainfall events make this more likely. Flood plumes affect water quality,
primarily through reduced clarity due to increased sediment and nutrients, and this can affect coral health.
• Crown-of-thorns starfish: crown-of-thorns starfish are a native coral predator, but when populations reach outbreak status
(approximately 15 starfish per hectare), they eat coral tissue faster than it can grow.
Cooler Mean sea surface temperature anomaly (˚C) Warmer Mass coral Cyclone Extreme Crown-of-thorns
Cooler Mean
Meansea
seasurface
surfacetemperature
temperatureanomaly
anomaly(˚C)
(˚C) Warmer bleaching
Mass coral
(max wind
Cyclone
rainfall event
Extreme
starfish outbreak
Crown-of-thorns
Cooler Warmer Mass coral Cyclone
category Extreme Crown-of-thorns
detected
bleaching (max wind rainfall
N event
Northern starfish outbreak
(Blue shades indicate cooler than average, red shades indicate warmer than average) bleaching (max
in wind
Reef
category
– rainfall event starfish outbreak
detected
(Blue
category
damaging NC Central
Northern detected
(Blueshades
shadesindicate
indicatecooler
coolerthan
thanaverage,
average,red
redshades
shadesindicate
indicatewarmer
warmerthan
thanaverage)
average) in Reef –
in Reef
wave –
potential)
N Northern
S Southern
CCCentral
damaging Central
damaging
wave potential)
wave potential) SSSouthern
Southern
NC
NNCC
The Great
Barrier Reef has NCS
3
S
experienced NCS
NCS SS 33
a variety of Trevor
disturbances Trevor
Trevor
over the past 5 2
22
5 2
22
55 55 S
decade. Yasi Zane Ita SS Penny
Yasi
Yasi Zane
Zane Ita
Ita Penny
Penny
2 2 2 5 2 2
22 22 22 55 22 22
Anthony Tim Dylan Marcia Linda Oma
Anthony Tim Dylan
Dylan Marcia Linda
Linda Oma
Oma
Anthony Tim Marcia
1 1 1 4 4 1 2
11 11 11 44 44 11 22
Tasha Oswald Edna Nathan Debbie Iris Owen
Tasha
Tasha Oswald
Oswald Edna Nathan
Nathan Debbie
Debbie Iris
Iris Owen
Owen
Edna
Northern Central Southern
Northern
Northern Central
Central Southern
Southern
1950–51 2010–11 2011–12 2012–13 2013–14 2014–15 2015–16 2016–17 2017–18 2018–19 2019–20
1950–51
1950–51 2010–11
2010–11 2011–12
2011–12 2012–13
2012–13 2013–14
2013–14 2014–15
2014–15 2015–16
2015–16 2016–17
2016–17 2017–18
2017–18 2018–19
2018–19 2019–20
2019–20
Last century Last decade
Last
Lastcentury
century Last
Lastdecade
decade
3
(a) (b) (c) (d)
Cooktown ! Graphical overview
of the key stresses
Cairns !
Cooktown !
and their variation
Mulgrave-Russell River
across the Reef
over recent
Tu
Ri
lly
ve
Cairns
r !
Mulgrave-Russell River
months.
Tu
Townsville !River
lly
Bu
rdek
in
Ri
Bowen !
Townsville
ve
r
!
Bu
rdek
Bowen !
Mackay
in !
Ri
ve
r
QLD Mackay !
QLD
zroy Ri
F it ve
r
Rockhamptonz!roy R
F it i ve
r
Rockhampton
Gladstone! !
Gladstone !
´ ´
Bundaberg !
Bundaberg !
0 300
0 300
Kilometres
Kilometres
SDC210308SDC210308
Maximum freshwater
Maximum exposure
freshwater ratio
exposure ratio Cumulative
Cumulativepotential Degree
cyclone Degree
potential cyclone Heating
Heating Crown-of-thorns
DaysDaysCrown-of-thorns starfish starfish
High: 1 High: 1 waveexposure
wave exposure # #
160 160
outbreak
outbreak status status
5 5cyclones
cyclones Severe outbreak
Severe outbreak
150
(°C Days)
150
(°C Days)
Low: 0 4 cyclones 140 Established outbreak
Low: 0 4 cyclones 140 Established outbreak
Great Barrier Reef Region and 130
Potential outbreak (culled)
Great Barrier
WorldReef Region
Heritage Area and
boundary 3 cyclones 120 130 Potential outbreak (culled)
World Heritage Area boundary 3 cyclones 110 120 Potential outbreak
Indicative reef 2 cyclones
100 110 Potential outbreak
IndicativeGreat
reef Barrier Reef 2 cyclones No outbreak (culled)
1 cyclone 90 100
No outbreak (culled)
Degree Heating Days
Catchment
Great Barrier Reef boundary 80 90 No outbreak
1 cyclone
0 cyclones 70
Degree Heating Days
Catchment boundary
River 80 No outbreak
60
0 cyclones 70
River 50
40 60
30 50
20 40
10 30
0 (No 20
data)
10
0 (No data)
Recent conditions across the Reef
(a) Maximum exposure to water from rivers on any single day between 1 October 2020 and 16 March 2021. Exposure
values represent the ratio of freshwater to seawater at the sea surface, calculated using aggregated model data from
the four kilometre resolution eReefs hydrodynamic model version 2.0 (GBR4_H2p0). Data from CSIRO.
(b) Estimated cumulative exposure to destructive waves (significant wave height of four metres or greater) from tropical
cyclones between 1 July 2020 and 16 March 2021. Additionally, some outer shelf reefs (e.g. between Townsville and
Cooktown) potentially experienced big swells from tropical cyclone Niran while it was outside the Reef. Data from AIMS.
(c) Accumulated Degree Heating Days (DHD) as of 16 March 2021. The map shows 14-day DHD accumulated over the
Reef during the period 1 December 2020 to 16 March 2021, based on the IMOS 2002-2011 climatology. This map is
likely to be an overestimate of the actual heat stress because of constraints due to missing data from persistent and
widespread cloud cover over the northern area of the Reef. Data from the Bureau of Meteorology.
(d) Crown-of-thorns starfish outbreak level observations between 1 July 2020 and 16 March 2021. Data from the Marine Park
Authority and AIMS.
2
2
Kimi
Kimi
Ongoing crown-of-thorns starfish outbreak
Ongoing crown-of-thorns starfish outbreak
JULY AUGUST SEPTEMBER OCTOBER NOVEMBER DECEMBER JANUARY FEBRUARY MARCH
JULY AUGUST SEPTEMBER OCTOBER NOVEMBER DECEMBER JANUARY FEBRUARY MARCH
2020–21
2020–21
4
What does this mean for coral?
During summer, surveys are conducted on the Great Barrier Reef to help us see how corals have been faring in different regions.
The information below summarises what we know about coral condition as of the end of March 2021. It is a summary of what has
happened over summer and gives the long-term context of the new observations. More comprehensive analyses and summaries will
be available later in the year. A timeline of key monitoring reports appears on the back page of this snapshot — for example, surveys
of additional inshore coral reefs will be conducted by the Marine Monitoring Program over the coming months. References for the
information below appear on the inside cover.
Cooktown
Northern Cooktown
Central Cooktown
Southern
TheCairns
northern region Cairns The
central region The southern region
includes coral reefs includes reefs from includes reefs
from Cape York down to just north of Cairns from south of the
Rockhampton Rockhampton Rockhampton
Lizard Island. down to south of the Whitsundays down to
Whitsundays. Reefs the Capricorn-Bunker
In-water surveys in this region have sustained significant area and out to the Swain Reefs.
(October to December): These surveys coral loss in the past due to mass coral
found high (30 to 50 per cent) levels of bleaching and severe tropical cyclone In-water surveys (August to September):
hard coral cover in the Cape Grenville Debbie in 2017 and the continued The Pompey Reef area was not due to be
area and moderate (10 to 30 per cent) southward spread of crown-of-thorns surveyed by the Long-term Monitoring
levels in the Princess Charlotte Bay starfish outbreaks. Program this year.
and Cooktown-Lizard Island areas.
Coral cover had increased on most of This summer, sample reefs off Cairns, Hard coral cover was very high (50 to
the visited reefs since they were last Innisfail and the Whitsunday Islands 75 per cent) in the Capricorn-Bunker
surveyed, although there were declines have been surveyed by the Long-term area overall, with increases on most
on 12 reefs. One reef had elevated levels Monitoring Program. Surveys of reefs surveyed reefs since they were last
of white syndrome disease. off Townsville are to occur in March- visited. Declines in cover were recorded
April, but results from these were not for two reefs, likely as a result of the 2020
An incipient outbreak of crown-of-thorns yet available when this snapshot was mass coral bleaching event. Numbers of
starfish was detected on one reef in prepared. crown‑of‑thorns starfish were low overall
the Cape Grenville area. Starfish levels and the trend was unchanged since
recorded at other surveyed reefs were In-water surveys (January to February): previous surveys.
low or zero. This summer’s surveys found hard coral
cover was moderate for the Cairns area Coral cover was moderate in the Swain
Low levels of hard coral bleaching were and had increased at all surveyed reefs. Reefs area, and had increased at most
observed on some reefs in the region, There has been strong recovery since survey reefs. Crown-of-thorns starfish
restricted to scattered individual colonies. 2020, which was the lowest hard coral were recorded at most surveyed reefs.
cover recorded since surveys began and Active outbreaks were recorded on three
Later, in January-February, anecdotal reefs and an incipient outbreak at a fourth
reports and Eye on the Reef program resulted from cumulative disturbances
between 2016 and 2019. Coral cover reef. At two reefs, starfish numbers had
surveys observed bleaching and reduced sufficiently for the reefs to be
fluorescing of corals on shallow reef was also moderate in the Innisfail area,
with surveyed reefs showing a mix of considered recovering rather than under
flats around several mid-shelf islands. active outbreaks.
In March, helicopter surveys in the increased, decreased and stable cover
Cooktown to Cape Melville area observed levels since they were last visited. Low levels of hard coral bleaching were
only low to moderate coral bleaching on Similarly, coral cover was also moderate observed on a few reefs in the Swain
some inshore and mid-shelf reefs, and in the Whitsunday Islands area, where Reefs area and most surveyed reefs in the
none on outer-shelf reefs. cover had increased on five reefs and Capricorn-Bunker area. Bleaching was
declined on five reefs. restricted to scattered individual colonies.
Numbers of crown-of-thorns starfish were Additionally, Eye on the Reef program
low and stable since previous surveys, surveys indicate levels of bleaching
with only two individuals recorded across remained low throughout summer across
31 surveyed reefs. a range of reefs in the southern region.
Low levels of hard coral bleaching were
observed on a few reefs in the region,
restricted to scattered individual colonies.
Summer 2020-21 was a relatively good year for the Reef’s corals. No major cyclone or prolonged high
sea temperature disturbance events occurred. Many reefs will have been able to continue their
recovery from past impacts.
Northern: pre-summer Central: pre-summer Southern: pre-summer
50 50 50
Coral cover (%)
Coral cover (%)
Coral cover (%)
40 40 40
30 30
30
20 20
20
10 10
10 Data from AIMS
1985 1990 1995 2000 2005 2010 2015 2020 1985 1990 1995 2000 2005 2010 2015 2020 1985 1990 1995 2000 2005 2010 2015 2020
5
What are we doing to help coral?
Supporting coral reef resilience is vital. Below are three examples of actions being taken to help coral.
Seeing the benefit of green zones
Green zones, or no-take marine reserves, protect
33 per cent of the Marine Park, and multiple lines
of evidence show they are effective. Studies
indicate reefs in green zones have fewer crown-of-
thorns starfish outbreaks and recover faster from
disturbances when compared to blue zones, which
are open to fishing. Green zones also provide benefits
for highly-prized fish, particularly coral trout. Recent
AIMS monitoring shows there are nearly twice as
many coral trout than in areas open to fishing, and
biomass (the total weight of all trout) is now 122 per
cent higher on reefs inside green zones. Coral trout in
marine reserves also provide larval subsidies to help
re-seed populations in areas open to fishing.
Harnessing coral slicks for recovery
Coral spawning events often happen only a few times
a year, over a couple of nights, following a full moon.
Drones are used to detect slicks of coral spawn in the
water. Scientists then collect samples and (in floating
ponds, transportable aquaculture systems, or back in
the lab) culture the larvae in the millions. The larvae
are then tagged before being deployed back onto the
reef. As part of the Reef Restoration and Adaptation
Program, researchers from universities and CSIRO will
use predictive modelling and 3D mapping to track larval
releases and see how effective the larval deployments are
at restoring reef areas compared to areas where larvae are
not deployed. The aim is to test protocols that could be
scaled up in the future to support recovery on damaged or
degraded reefs. Slick spotting from the air
Asking people what they value
Changes in environmental threats and impacts to the
Great Barrier Reef mean that Reef communities are
changing the way they use and protect this Aussie icon.
Reef managers require an up-to-date understanding of
how people value, perceive and interact with the Reef,
in order to manage adaptively and protect community
values while responding to emerging threats.
SELTMP is the Social and Economic Long-Term
Monitoring Program for the Great Barrier Reef, led by
CSIRO. Its researchers have conducted large-scale
surveys of Reef user groups in 2013 (8300 people) and
2017 (4000 people).
In May-June 2021, SELTMP will be running new surveys,
seeking participation and input from thousands of
residents between Bundaberg and Cape York.
6
What can you do?
See the Reef. Love the Reef. Protect the Reef.
The Reef is facing unprecedented pressures, yet its astounding beauty continues to inspire people. We
acknowledge the impact that COVID-19 is having on international opportunities to visit the Great Barrier Reef. As
opportunities to visit in a safe way increase, we encourage people from around the world to come and be inspired
by the Reef’s beauty and to take actions to protect it for future generations to enjoy.
Think globally, act locally.
Every effort, no matter how small, collectively matters. Be it in your home or business, all actions matter. Visit
gbrmpa.gov.au for steps you can take.
Understand and follow protection rules for the Great Barrier Reef.
Measures like zoning (access restrictions), permits, no anchoring areas, and extraction limits protect the Great
Barrier Reef for the long term. Adopting a ‘protect your patch’ approach and making the most of user-friendly tools
like the Eye on the Reef app and public moorings will help you help the Reef.
Reef health monitoring
Each year, data on the health of the Reef’s corals are collected, analysed, and shared. The timing of data collection periods, report
releases and related workshops is shown below.
Jul-Sep Oct-Dec Jan-Mar Apr-Jun
Marine Monitoring Marine Monitoring
Long-term Monitoring Program surveys
Program surveys Program surveys
(mainly mid and outer shelf reefs)
(inshore reefs) (inshore reefs)
Eye on the Reef
(surveys/submissions)
Long-term
Monitoring Program Post-summer Reef
Pre-summer workshop
annual summary snapshot
(annual)
report (annual)
(annual)
Marine Monitoring
Program reports
(annual)
Great Barrier Reef Marine Park Authority Australian Institute of Marine Science CSIRO
gbrmpa.gov.au aims.gov.au csiro.au
info@gbrmpa.gov.au reception@aims.gov.au csiroenquiries@csiro.au
+61 7 4750 0700 +61 7 4753 4444 +61 3 9545 2176You can also read
