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


Summary

  • Overall, reefs had moderate levels of coral bleaching (10-30% of total hard coral cover).
  • Reefs that were surveyed at the end of the 2016/17 summer had variable impacts from coral bleaching, with some reefs showing high to very high levels of bleaching in particular reef zones.
  • Median reef-wide live coral cover had increased across the sector, despite declines on three of seven reefs that were surveyed.
  • Crown-of-thorns starfish (COTS) activity continues to increase on reefs in this sector.
  • A coral disease outbreak was recorded at Taylor Reef.  

Figure 1:  Map showing location of reefs in the Innisfail sector. Click on figure to go to AIMS Spatial Maps and click on symbols for information on individual reefs

Table 1: Overview of results obtained from manta tow surveys of reefs in the Innisfail sector.

Innisfail Sector Summary Trend since last survey
Median Coral Cover Moderate (10-30%) Increased
COTS status: 2 Active Outbreaks, 1 Incipient Outbreaks Increased
Coral bleaching: Moderate Increased

As part of the Long Term Monitoring Program (LTMP), six reefs in the Innisfail sector of the Great Barrier Reef (GBR) were surveyed for coral cover and abundance of the coral feeding COTS Acanthaster planci using the manta tow technique. Median reef-wide live coral cover (coral cover) continues to increase on reefs in the sector that are recovering from the effects Severe Cyclone Yasi (category 5) in February 2011 (Table 1). Results for individual reefs are given in Table 2.

COTS activity continues to increase on reefs in this sector. Active outbreaks were observed at Taylor and Gilbey Reefs. Coral cover had declined on Gilbey Reef likely due to COTS feeding activity. On Taylor Reef coral cover had increased since the last survey but is likely to decline since outbreak densities of COTS are still present on this reef. An incipient outbreak was recorded at Flora Reef where coral cover was stable, but may also decline in future due to COTS. Low numbers of COTS were also observed on Feather Reef but at densities that are unlikely to cause coral cover to decline.

Some reefs in this sector were surveyed before the 2016/17 summer bleaching event, while others were surveyed after. Bleaching was limited to small numbers of scattered individual coral colonies on parts of those reefs that were surveyed beforehand (Feather, Flora, Taylor and Gilbey Reefs). In contrast, bleaching was widespread on the two reefs surveyed after the 2016/17 summer bleaching. Wardle Reef was particularly severely affected: on some parts of the reef, bleaching affected 50-75% of total coral cover. There was also significant recent coral mortality on this reef and coral cover had declined since the previous survey, likely from mortality due to summer bleaching. Similarly on Moss Reef bleaching was high in some zones, affecting 30-50% of total coral cover, and coral cover had also declined since the previous survey. White syndrome was observed on all reefs but generally below outbreaks levels (incidence of disease at a higher rate than normally recorded during manta tow surveys). Signs of black-band disease were recorded at Feather Reef.

 

Table 2: Summary of manta tow surveys for reefs in the Innisfail sector. Arrows indicate the trend in live coral cover and A. planci since last survey;   = increase,   = decrease, “  ” = no change. Reef status refers to COTS impact where 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
FEATHER Mid 51 2016 1  0.02 20-30% 0-5% NO
FLORA Mid 50 2007 19  0.38 5-20% 0-5% IO
TAYLOR Mid 50 2016 63  1.26 20-30%  0-5% AO
GILBEY Outer 51 2005 95  1.86 20-30%  0-5%  AO
MOSS Outer 54 2005 0 0 20-30%  0-5% NO
WARDLE Outer 58 2016 0 0 5-10%  0-5%  NO

Dates: 19th - 22nd December 2016 and 27th - 28th April 2017

Vessel: RV Cape Ferguson

Survey leaders: Kate Osborne  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.

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

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

Image 1: COTS activity continues to increase on reefs in this sector with a number of reefs experiencing Active Outbreaks. This photo was taken on Wardle Reef.

Image 2: Coral bleaching affected some reefs badly. This panorama of the reef slope taken on Moss reef shows a huge variation in response of corals to summer heat stress. Some corals are bleached white, some corals are fluorescent and some corals are dead, while others appear unaffected, with everything in between.

Image 3: Wardle Reef was particularly badly affected by coral bleaching and coral cover declined as a result.