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


Summary

  • Overall moderate levels of coral bleaching (10-30% of total hard coral cover).
  • Impact of the summer 2016/17 bleaching event varied, some reefs had low levels of bleaching while a high proportion of corals were bleached at other reefs.
  • Median reef-wide live coral cover had increased on four of seven reefs since they were last surveyed.
  • Coral cover had declined on two reefs, John Brewer and Rib Reefs. The decline on Rib Reef was due to a crown-of-thorns starfish (COTS) outbreak.
  • Coral disease outbreaks were recorded at Davies and John Brewer Reefs.  

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

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

Townsville Sector Summary Trend since last survey
Median Coral Cover Moderate (10-30%) Increased
COTS status: 1 Active Outbreaks, 0 Incipient Outbreaks Increased
Coral bleaching: Moderate Increased

As part of the Long Term Monitoring Program (LTMP), seven reefs in the Townsville 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) increased in the sector (Table 1) as reefs continue to recover from Severe Tropical Cyclone Yasi in February 2011. Results for individual reefs are given in Table 2.

A large COTS outbreak was observed at Rib Reef. COTS were also observed on John Brewer Reef and during scuba search surveys of Chicken Reef, indicating increasing COTS activity on reefs in this sector.

Qualitative assessments of bleaching from manta tow surveys revealed that bleaching was widespread, affecting all reefs in the sector, generally at a moderate level (10 to 30% of total hard coral cover). The highest incidence of bleaching was recorded at Havannah Island Reef where it affected 50-75% of total hard coral cover. Moderate (10 to 30%) to high levels (30-50%) of bleaching were also recorded on parts of Dip, Myrmidon and Rib Reefs. Bleaching was generally widespread on the reef slopes of reefs throughout the sector, from the reef flats, reef crest and slope down to below 10m. White syndrome disease outbreaks (incidence of disease at a higher rate than normally recorded during manta tow surveys) were observed on the first flank of Davies Reef and the front and second flank of John Brewer Reef. An outbreak of black-band disease was also recorded on the second flank of John Brewer Reef.

 

Table 2: Summary of manta tow surveys for reefs in the Townsville 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
HAVANNAH IS Inner 27 2013 0 0 20-30%  0-5% NO
DAVIES Mid 47 2015 0  0 20-30%  0-5% NO
JOHN BREWER Mid 74 2016 1  0.01 30-40%  0-5% NO
RIB Mid 34 2016 38  1.12 20-30%  0-5% AO
CHICKEN Outer 46 2016 0 0 10-20% 0-5% NO
DIP Outer 43 2015 0 0 10-20%  0-5% NO
MYRMIDON Outer 52 2015 0 0 10-20%  0-5% NO

Dates: 24th April - 14th May 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. planci for survey reefs in the Townsville sector of the GBR.

Image 1: Coral bleaching was widespread throughout the sector. A high proportion of coral cover was affected on some reefs, such as Havannah Island Reef.

Image 2: John Brewer Reef was less affected by coral bleaching than other reefs in the region and coral cover was high.

Image 3: There was a large COTS outbreak on Rib Reef. Coral cover has declined as a result.

This footage highlights the effect that the 2016/17 summer bleaching event had on the corals growing on the fringing reef that surrounds Havannah Island in the Palm Island Group. Corals that are brightly coloured, fluorescent and bleached white are showing symptoms of heat stress. The dull coloured corals covered in turf algae have died recently, likely due to bleaching, while there are other normal-coloured corals that appear unaffected.