- Hard coral cover has declined since 2017 to historically low values (0-10%)
- Recent coral losses are likely due to the 2016 and 2017 bleaching events
- No coral feeding crown-of-thorns starfish, Acanthaster solaris* were observed
Figure 1: Map showing location of reefs in the Cairns sector. Click on figure to go to AIMS Spatial Maps for information on individual reefs.
Table 1: Overview of results obtained from manta tow surveys of reefs in the Cairns sector
|Cairns Sector||Summary||Trend since last survey|
|Median Coral Cover||Low (0-10%)||Decreased|
|COTS status:||No Outbreaks||Stable|
As part of the Long Term Monitoring Program (LTMP), manta tow surveys of coral cover and abundance of the coral feeding crown-of-thorns starfish (COTS), Acanthaster solaris, were completed on five reefs in the Cairns sector of the Great Barrier Reef (GBR). Detailed surveys for benthic organisms, visual census of fishes and surveys for agents of coral mortality (scuba search) were also made on these reefs. Preliminary results of the manta tow and scuba search surveys are presented in this report. Manta tow surveys (Table 1) showed that median reef-wide live coral cover (coral cover) had declined at four reefs and increased at one reef. The coral declines had occurred since 2016 and/or 2017, suggesting that major bleaching events in those two years were the likely cause.
Low levels of coral disease were observed on all five reefs during manta tow surveys. No COTS were seen.
Scuba surveys recorded low levels of coral bleaching, which were limited to scattered individual colonies. There was widespread evidence of coral mortality in the relatively recent past, presumably from coral bleaching over the previous two summers. The number of cases of white syndrome coral disease on all reefs was lower than in previous surveys and incidences were generally at the lower end of the historical range. Incidences of three other coral diseases (black-band, brown-band and skeletal eroding band) were negligible.
Details of the manta tow method can be found in the Standard Operational Procedure No. 9 [AIMS Research - Crown-of-thorns Starfish and Coral Surveys - Standard Operational Procedure 9]. Further details of the monitoring program design, sampling methods and a full explanation of the A. planci outbreak terminology can be found on the AIMS website.
*Note: genetic studies show that there are at least four species of COTS. These are the North and South Indian Ocean species (A. planci and A. mauritiensis), a Red Sea species (not yet named) and a Pacific species. The latter is found on the Great Barrier Reef and has been putatively named Acanthaster solaris (Haszprunar et. al. 2017).
Table 2: Summary of manta tow surveys of reefs in the Cairns sector. Arrows indicate the trend in live coral cover and A. solaris since last survey; ▲= increase, ▼= decrease, “ ” = no change.
|Reef||Shelf Position||Tows||Previous survey year||A. solaris||A. solaris per tow||Median Live Coral Cover||Median Soft Coral Cover||Reef Status|
|ARLINGTON||Mid||60||2017||0 ▼||0||5-10% ▼||5-10% ▼||NO|
|THETFORD||Mid||38||2017||0||0||5-10% ▼||5-10% ▼||NO|
|AGINCOURT NO.1||Outer||32||2017||0||0||10-20% ▲||0-5%||NO|
|ST. CRISPIN||Outer||90||2017||0||0||0-5% ▼||0-5%||NO|
Figure 3: Effects of marine park zoning. Comparisons of the median values of nine variables through time, based on surveys of fixed sites on matched pairs of reefs in this sector. One reef in each pair was rezoned so fishing was prohibited (Green zone) in 2004, the other reef in each pair remains open to fishing (Blue zone). Error bars are 95% credible intervals.
Figure 2: - Sector-wide changes in coral cover and the numbers of A. solaris for survey reefs in the Cairns sector of the GBR.
Image 1: – At Thetford Reef there was a mix of live corals and dead standing colonies that had presumably died from heat stress
Image 2: – Some coral communities at Agincourt No.1 Reef had largely escaped the effects of bleaching.
Image 3. – Despite low coral cover at St. Crispin Reef, herbivorous fishes such as these Steephead parrotfish (Chlorurus microrhinos), were abundant.