27th April 2017
- Recovery of hard coral cover continues following Cyclone Hamish in 2009.
- Recovery slower at some locations due to persistent populations of crown-of-thorns starfish (COTS).
- Widespread bleaching was observed at low to moderate levels, particularly affecting shallow and sheltered (back reef) habitats.
- COTS activity decreased from previous survey, with two individuals observed at one reef.
Figure 1 - Map showing location of reefs in the Pompey sector of the Great Barrier Reef. Click on figure to go to AIMS Spatial Maps for information on individual reefs.
|Pompeys Sector||Summary||Trend since last survey|
|Median Coral Cover||Moderate (10-30%)||Increased|
|COTS status:||No Outbreaks||Decreased|
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 in February 2017 on five reefs in the Pompey sector of the Great Barrier Reef (GBR; Fig. 1). Median reef-wide live coral cover increased at four of five reefs (Table 1), in conjunction with a decrease in crown-of-thorns starfish activity (Fig. 2). A decrease in coral cover at Cannan Reef may not necessarily be recent, as it was previously surveyed in 2005, when an Incipient Outbreak of COTS was recorded. Only two A. planci were observed during manta tow at one of the five reefs in 2017 (Table 1).
Qualitative assessments of bleaching from manta tow surveys in 2017 revealed that bleaching was widespread at a low to moderate level. Generally, bleaching was low (up to 10%) below 6m depth and in exposed (front reef) and steep-walled habitats. Bleaching prevalence increased in shallow (<6m) and sheltered (back reef) habitats, with up to 50% of hard corals showing signs of heat stress in some habitat patches. The outer-shelf reef, Ben Reef, was least affected by bleaching, with very low levels (<5%) observed in all habitats surveyed.
Table 1 - Summary of manta tow surveys for reefs in the Pompey sector. Arrows indicate the trend in live coral cover and A. planci since last survey; ▲ = increase, ▼ = decrease, " " = no change.
|Reef||Shelf Position||Tows||Previous survey year||A. planci||A. planci per tow||Median Live Coral Cover||Median Soft Coral Cover||Reef Status|
|20-354||Mid||21||2011||2 ▲||0.1||30-40% ▲||0-5%||NO|
|CANNAN||Mid||21||2005||0 ▼||0||10-20% ▼||0-5%||NO|
|CREAL||Mid||19||2013||0 ▼||0||5-10% ▲||0-5%||NO|
Dates: 16th February – 8th March 2017
Vessel: RV Cape Ferguson
Survey leader: Kerryn Johns
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 for survey reefs in the Pompey sector of the GBR.
Figure 3 – The front reef slope at Ben Reef flourishing with tabulate Acropora colonies, showing strong recovery from the impacts of Cyclone Hamish in 2009. There was very little evidence of the effects of bleaching on this outer shelf reef in the early stages of the bleaching event unfolding in February and March 2017.
Figure 4 – A pale Acropora colony on the reef slope of Creal Reef – a sign of heat stress. Up to 10% of hard corals were bleached in some habitat patches on most reefs surveyed in this sector. Sheltered (back reef) habitats and shallow habitats were particularly affected.
Figure 5 – The consolidated rubble remnants of branching Acropora colonies at Credlin Reef form a new substrate for corals to colonise. Coral cover at Credlin Reef was reduced to very low levels by crown-of-thorns starfish (COTS). The skeletons of corals consumed by COTS weaken and collapse over time. Further, corals and coral skeletons were subject to physical destruction caused by Cyclone Hamish in 2009. In this shallow, sheltered habitat, many of the young corals colonising the rubble substrate were showing signs of heat stress in February 2017