Report on surveys of the Swains sector of the Great Barrier Reef


Summary

  • Some reefs in this sector remain to be surveyed in this reporting year

Figure 1: Map showing location of reefs in the Swain 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 Swain sector.

Swains Sector Summary Trend since last survey
Median Coral Cover High (30-50%) Decreased
COTS status: 0 Active Outbreaks, 1 Incipient Outbreaks Increased
Coral bleaching: None 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 solaris* were completed using the manta tow technique on four reefs in the Swain sector of the Great Barrier Reef (GBR). Preliminary results of the manta tow surveys are presented in Table 2. These show that median reef-wide live coral cover (coral cover) had increased at three reefs and remained stable on one (Reef 21-139). Coral cover ranged from moderate (20-30%) to very high (63-75%).

Outbreak levels of COTS were observed on Reef 21-187. At the time of survey the population was localized, as was the impact on coral cover. Coral cover had increased overall on Reef 21-187 since the last survey in 2016. Surveyed reefs showed no obvious signs of coral mortality from bleaching in the past year. Low levels of white syndrome disease were recorded at all four reefs.

*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), Red Sea species (not yet named) and a Pacific species. The range of the Pacific includes the Great Barrier Reef and it has been provisionally named Acanthaster solaris (Haszprunar et. al. 2017).

Table 2: Summary of manta tow surveys of reefs in the Swain 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
21-139 Mid 54 2016 0 0 30-40% 0-5% NO
21-187 Mid 39 2016 20  0.51 20-30%  0-5% IO
21-550 Mid 36 2016 0 0 30-40%  0-5% NO
22-084 Mid 17 2016 0 0 63-75%  0-5% NO

Dates: 11th – 27th October 2017

Vessel: RV Cape Ferguson

Survey leader: 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.

For enquiries, please contact monitoring@aims.gov.au

Figure 2: Sector-wide changes in coral cover and the numbers of A. solaris for survey reefs in the Swain sector of the GBR.

Image 1: Very high coral cover and a diversity of species was recorded around the perimeter of Reef 22-084 as recovery from a COTS outbreak prior to 2006 continues.

Image 2: Crown-of-thorns starfish were locally abundant on Reef 21-187 causing local reduction in coral cover.

Image 3: The reef slope at reef 21-550 shows a diversity of hard corals including foliose, tabulate, branching and massive growth forms.