Report on surveys of the Cairns sector of the Great Barrier Reef
- Sector-wide hard coral cover was moderate (10-30%) and stable.
- Impacts from the 2016 bleaching event were patchy, with noticeable coral declines on some reefs but not on others.
- Crown-of-thorns starfish (COTS) activity had markedly decreased with only one individual observed.
|Cairns Sector||Summary||Trend since last survey|
|Median Coral Cover||Moderate (10-30%)||Stable|
|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 planci, were completed on 12 reefs in the Cairns sector of the Great Barrier Reef (GBR; Figure 1) during multiple trips between early September and late December 2016. Median reef-wide live coral cover (coral cover) increased at two reefs and remained stable at six other reefs. The highest coral cover (30-40%) was recorded at the inshore Low Islets Reef (Table 1). Coral cover had decreased at the four remaining reefs (Hastings, Agincourt No.1, Opal (2) and St. Crispin; see Table 2), all situated near the outer shelf of the GBR. These declines were most probably the result of coral bleaching earlier in 2016. Overall, mean sector-wide live coral cover was stable around 20%, a relatively good value based on mean cover since the early 1990’s (Figure 2). This suggests that coral mortality from the 2016 beaching event was patchy in the Cairns sector, and was balanced by coral gains on unaffected reefs. Only one single COTS was observed (at Arlington Reef) during manta tow surveys, which represents a marked decline in COTS numbers from recent past surveys (Figure 2). As in previous waves of outbreaks, the COTS populations appear have spread further south to reefs near Innisfail and Townsville.
Table 2: Summary of manta tow surveys for reefs in the Cairns sector. Arrows indicate the trend in live coral cover and A. planci numbers since last survey; = increase, decrease, “ no arrow ” = no change. For the outbreak status of COTS NO = No Outbreak and RE = Recovering from a previous outbreak.
|Reef||Shelf Position||Tows||Previous survey year||A. planci||A. planci per tow||Median Live Coral Cover||Median Soft Coral Cover||Reef Status|
|FITZROY IS||Inner||38||2012||0||0||20-30%||10-20% ↑||NO|
|GREEN IS||Inner||43||2015||0 ↓||0||5-10% ↑||5-10%||RE|
|ARLINGTON||Mid||60||2016||1 ↓||0.02||10-20%||10-20% ↓||NO|
|HASTINGS||Mid||74||2016||0||0||10-20% ↓||5-10% ↓||NO|
|MICHAELMAS||Mid||112||2015||0 ↓||0||10-20%||10-20% ↑||NO|
|SAXON||Mid||20||2007||0||0||20-40% ↑||10-20% ↑||NO|
|THETFORD||Mid||38||2016||0 ↓||0||20-30%||10-20% ↓||NO|
|AGINCOURT NO.1||Outer||39||2016||0||0||5-10% ↓||0-5% ↓||NO|
|OPAL (2)||Outer||74||2015||0||0||10-20% ↓||5-10%||RE|
|ST. CRISPIN||Outer||84||2016||0||0||5-10% ↓||0-5% ↓||NO|
Dates: 6th September to 19th December 2016
Vessel: RV Cape Ferguson
Survey leaders: Alistair Cheal and Ian Miller
Details of the manta tow method and results can be found here.
Click here for further details of the monitoring program design, sampling methods and a full explanation of the A. planci outbreak terminology.
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Figure 2: Sector wide changes in coral cover and the numbers of A. planci through time for all survey reefs in the Cairns sector of the GBR.
Image 1: Coral communities on parts of Agincourt Reef (No.1) had been affected by the extensive bleaching of the northern GBR a few months prior to these surveys. Such areas had many dead or partially dead coral colonies.
Image 2: The luxuriant coral cover along many sections of Low Islets Reef, an inshore reef not far from Port Douglas, shows that this reef was largely unaffected by the 2016 bleaching event and highlights the patchiness of bleaching related coral mortality in the Cairns sector.