15 March 2017
Summary
- Strong recovery in hard coral cover on most reefs since storms and Cyclone Hamish in 2008/09
- Little evidence of significant impact of the 2016 bleaching event
- One coral feeding crown-of-thorns starfish, Acanthaster planci observed at one reef
Figure 1 - Map showing location of reefs in the Capricorn-Bunker sector. Click on figure to visit AIMS Spatial Maps for information on individual reefs.
|
Capricorn-Bunker Sector |
Summary |
Trend since last survey |
|
Median Coral Cover: |
High (30-50%) |
Increased |
|
COTS status: |
No Active Outbreak |
Decreased |
|
Coral disease: |
Overall Low |
Increased |
|
Coral bleaching: |
Very Low |
Decreased |
As part of the Long Term Monitoring Program (LTMP), surveys of coral cover and abundance of the coral feeding crown-of-thorns starfish (COTS), Acanthaster planci, were completed on four reefs in the Capricorn-Bunker sector of the Great Barrier Reef (GBR) using the manta tow technique. Results (Table 1) showed that median reef-wide live coral cover (coral cover) had remained stable at two reefs and increased at two reefs, indicating strong recovery since storm damage in 2008/09.
A single A. planci was observed on one reef, Lady Musgrave Island. Small numbers of A. planci have been observed along the back reef at Lady Musgrave Island in previous surveys, but these have always been well below outbreak levels. Overall A. planci activity had declined in this sector compared to the last survey in 2015.
Surveys in 2017 recorded very low levels of coral bleaching, which was limited to scattered individual colonies on one reef (One Tree Island). There was no evidence of mortality from coral bleaching the previous summer. Although all reefs surveyed had a higher incidence of white syndrome coral disease since the previous surveys, levels were low to moderate and no doubt reflect the increased cover of table and branching Acropora corals, which are known to be among the most susceptible corals to this disease. Higher than average incidence of brown-band coral disease was also observed at all the reefs surveyed in 2017.
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.
Table 1 - Summary of manta tow surveys of reefs in the Capricorn-Bunker sector. Arrows indicate the trend in live coral cover and A. planci since last survey; ▲= increase, ▼= decrease,“ ” = no change.
|
Reef |
Shelf Position |
Tows |
A. planci |
A. planci per tow |
Median Live Coral Cover |
Median Dead Coral Cover |
Median Soft Coral Cover |
Reef Status |
|
Outer |
47 |
0 |
0 |
40-50% |
0% |
0-5% |
NO |
|
|
Outer |
69 |
1 |
0.01▼ |
30-40% |
0-5% |
0-5% |
NO |
|
|
Outer |
78 |
0 |
0 |
30-40% ▲ |
0-5% |
0-5% |
NO |
|
|
Outer |
45 |
0 |
0 |
50-63% ▲ |
0% |
0-5% |
NO |
Figure 2 - Sector wide changes in coral cover and the numbers of A. planci through time for all survey reefs in the Capricorn-Bunker sector of the GBR. Orange points are the mean coral cover estimates and the orange line and envelope are the modelled trends through time (mean ± 1 S.E.) from a Generalised Additive Model (GAM). Blue bars are the number of A. planci (mean ± 1 S.E.). All data are estimates per two-minute manta tow, averaged across all survey reefs in the sector. The dotted horizontal blue line indicates Incipient Outbreak density threshold for A. planci (0.22 A. planci /tow) that may be expected to reduce regional coral cover. The dotted red line indicates Active Outbreak densities of A. planci (1.0 A. planci/tow) that are certain to reduce regional coral cover.
Figure 3 – Recovery from storm damage at One Tree Island. a. Reef areas that previously had high cover of mainly Acropora corals were reduced to bare substrate in 2008/09 after storms and Cyclone Hamish damaged the reef b.The surveys in January 2017 found that hard corals, particularly table Acropora spp., have recolonised the reef slope.
Figure 4 – A typical scene from the Capricorn-Bunker reefs, showing a shallow reef slope with very high cover of table Acropora spp, punctuated by sandy gullies.
