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


Summary

  • Hard coral cover increased on all reefs since previous survey, indicating recovery following Cyclone Hamish in 2009 (outer-shelf reefs) and Cyclone Ului in 2010 (all shelf positions).
  • Bleaching was low to moderate and widespread, particularly affecting shallow and sheltered habitats on inshore reefs.
  • No population outbreaks of crown-of-thorns starfish, Acanthaster planci.
 

Figure 1 - Map showing location of survey reefs in the Whitsunday sector of the Great Barrier Reef. Click on figure to go to AIMS Spatial Maps for information on individual reefs.

 

Whitsunday Sector Summary Trend since last survey
Median Coral Cover Moderate (10-30%) Increased
COTS status: No Outbreaks Stable
Coral bleaching: Low Increased

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 ten reefs in the Whitsunday 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) increased on all reefs, indicating recovery from Cyclone Hamish in 2009, which impacted outer-shelf reefs, and Cyclone Ului in March 2010, which impacted all survey reefs in this sector.

A single A. planci was observed during SCUBA search surveys on each of two reefs. Feeding scars from A. planci were also observed at four other reefs in the sector. Overall A. planci activity remained stable at very low levels.

Surveys in 2017 revealed widespread coral bleaching. Bleaching affected up to 10% hard coral cover at intensive survey sites. Qualitative assessments of bleaching from manta tow surveys revealed that bleaching was at a low to moderate level. Generally, bleaching was very low (up to 10%) on outer-shelf reefs, below 6m depth and in exposed and steep-walled habitats. Bleaching increased closer to shore and in shallow (<6m) and sheltered (back reef) habitats, with more than 50% of hard corals showing signs of heat stress in some habitat patches. On inshore and outer shelf reefs, occurrence of coral disease and density of the corallivorous snail Drupella sp. was low. On mid-shelf reefs both the occurrence of coral disease and density of Drupella sp. had increased since the previous survey to moderate levels.

Table 1 - Summary of manta tow surveys of reefs in the Whitsunday 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
BORDER IS (A) Inner 55 2013 0 0 10-20%  30-40%  NO
HAYMAN IS Inner 35 2013 0 0 20-30%  20-30%  NO
LANGFORD AND BIRD IS'S Inner 28 2013 0  0 10-20%  20-30%  NO
19-131 Mid 55 2015 0 0 20-30%  0-5% NO
19-138 Mid 32 2015 0 0 30-40%  0-5% NO
20-104 Mid 24 2015 0 0 30-40%  0-5% NO
HARDY Mid 125 2004 0  0 30-40%  0-5% NO
HYDE Outer 50 2015 0 0 10-20%  0-5% NO
REBE Outer 32 2015 0 0 10-20%  0-5% NO
SLATE REEF Outer 39 2015 0 0 10-20%  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.

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 Whitsundays sector of the GBR.

 

Figure 3 – Scattered hard coral colonies contribute to coral recovery following damage caused by Cyclone Ului in March 2010 on the reef slope of Reef 19-131. Some colonies are showing signs of heat stress in the form of vibrant fluorescence or pale branch tips.

 

Figure 4– Branching and bottlebrush growth forms of Acropora and the fire coral Millepora unaffected by bleaching in deeper reef slope habitat (~8m) at Hayman Island Reef.

 

Figure 5 – Branching Acropora; bleached due to high sea surface temperatures in shallow reef slope habitat (~3m depth) at Border Island Reef.

 

Figure 6 – A crown-of-thorns starfish on the reef slope (~8m depth) at Langford-Bird Reef.