Report on surveys of the Cairns and Townsville sectors of the Great Barrier Reef

Dates: 26^th Feb to 16^th March 2015

Vessel: RV Cape Ferguson

Survey leader: Kerryn Johns

As part of the Long Term Monitoring Program (LTMP), surveys of reef-wide live hard coral cover and abundance of the coral feeding crown-of-thorns starfish (COTS), Acanthaster planci, were completed on ten reefs in the Cairns sector of the Great Barrier Reef (GBR) using the manta tow technique. Intensive scuba surveys of benthic organisms and fishes as well as scuba searches for agents of coral mortality were also completed on eight reefs in the Cairns sector and two reefs in the Townsville sector. Preliminary results of manta tow surveys and scuba searches are presented in this report.

Median reef-wide cover of living coral (henceforth coral cover) was moderate (10-30%) at seven reefs and low (0-10%) at three reefs in the Cairns sector. Coral cover remained at similar levels to the previous survey at five reefs and had increased on one mid-shelf reef and one outer-shelf reef. Coral cover had decreased since the previous survey at three mid-shelf reefs where COTS subject to COTS outbreaks (two Incipient Outbreaks (IO) and one Active Outbreak (AO) were recorded on mid-shelf reefs). In 2013 outbreak levels of COTS were recorded on seven of the eleven survey reefs in this sector. This was the first time outbreaks had been recorded since 2002. COTS control programs have substantially reduced COTS populations at some locations, particularly popular tourist destinations. COTS were observed in intensive scuba surveys at one mid-shelf reef and one inshore reef in 2015, compared with one mid-shelf and three inshore reefs in 2013.

White syndrome disease (a disease-like necrosis found particularly on tabulate Acropora spp.) was generally rare in the Cairns Sector and other diseases including black-band disease, brown band disease and skeletal eroding band disease were not observed at scuba survey sites. The density of Drupella spp. (coral feeding snails) was generally low and similar to the long-term average. Coral bleaching was widespread and individual pale colonies of a range of coral genera, particularly Seriatopora spp. were recorded.

Intensive scuba surveys at two reefs in the Townsville sector also revealed widespread coral bleaching affecting individual colonies from a range of coral genera. Similar to the Cairns Sector, Seriatopora spp. were most prominently affected. No COTS were observed in scuba surveys at these two reefs. Coral diseases were rare and density of Drupella spp. was low and similar to the long-term average. Manta tow surveys are yet to be conducted at these reefs in 2015. However, at the last survey coral cover at these locations was in a recovery phase from Cyclone Yasi (Rib Reef) and a COTS outbreak (John Brewer Reef).

A summary of the results is presented in Tables 1 to 5. 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 COTS outbreak terminology can be found on the AIMS website.

Perimeters of ten reefs in the Cairns sector were surveyed using manta tow (Table 1). COTS were recorded at Incipient Outbreak levels of 0.53 and 0.42 COTS per tow at Pickersgill Reef and Evening Reef respectively. An Active Outbreak was recorded at Mackay Reef with an average of 1 COTS observed per two minute manta tow. The presence of COTS at these reefs coincided with a decline in coral cover since the previous survey. Single individual COTS were observed at Green Island Reef and at Michaelmas Reef. In 2013 an Incipient Outbreak was recorded for Green Island Reef, however, COTS control programs appear to have reduced these numbers over the past two years. Coral cover at Pickersgill Reef and Mackay Reef was moderate in 2015 (Table 1), while coral cover at Evening Reef (last surveyed in 2007) was low (5-10%). Coral cover was also low at Green Island and Agincourt Reef No.1, and was moderate at Hastings Reef, St. Crispin Reef and Norman Reef. Coral cover was moderate at Michaelmas Reef (10-20%) and Opal Reef (2) (20-30%) and had increased at the latter since last surveyed in 2013. These levels of coral cover continue to hover around the overall long-term average for all reefs in this sector.

Table 1. Summary of manta tow surveys for reefs in the Cairns sector.

Three sites at each of eight reefs were surveyed in detail using scuba (Table 2). At the intensive survey sites, seven COTS, mostly sub-adult and adult sized, were observed at Mackay Reef, and four large adult COTS were found at Low Islets Reef. This was a substantial reduction from the previous survey in 2013 when 25 individuals, mostly small sub-adults, were found at Mackay Reef and 17 individuals ranging in size were recorded at Low Isles. Accordingly, associated feeding scars were substantially fewer than the 2013 survey. No COTS were observed at Green Island or Fitzroy Island intensive survey sites, the latter of which hosted a large population (57 individuals, mostly sub-adults) at the time of the 2013 survey. This reflects COTS control programs that have targeted these popular tourist destinations since the last survey. The incidence of coral disease was generally rare at survey sites in the Cairns Sector, though white syndrome was recorded on 29 colonies at Mackay Reef. Density of Drupella spp. at Mackay Reef was slightly elevated from the long-term average, but still quite low.

Coral bleaching was observed at all survey reefs in the Cairns Sector (Table 3). At some locations, coral bleaching was observed along all fifteen transects but was restricted to individual colonies. The most sensitive corals were Seriatopora spp., though individual colonies from a range of other genera were also impacted. Two more reefs in the Cairns sector remain to be surveyed in 2015.

Table 2. Summary of results of scuba search surveys of reefs in the Cairns sector.

I=inner, M=mid, O=outer, WS = White Syndrome, BBD = Black Band Disease, BrB = Brown Band Disease, SEB = Skeletal Eroding Band Disease

Table 3. Summary of coral bleaching observations for reefs in the Cairns sector

Sites at two Townsville reefs, Rib Reef and John Brewer Reef, were surveyed in detail using scuba (Table 4). Three scars from COTS feeding were recorded at John Brewer Reef, though no COTS were seen. Coral cover at John Brewer Reef has been low since it was reduced to 1% in 2004 by COTS feeding activity. Between 2011 and 2013 coral cover had doubled from 5% to 10%, indicating recovery was underway. No COTS were observed at Rib Reef in 2015. Only one small individual was recorded in the previous survey in 2014, though 27 scars attributed to COTS feeding were recorded. Coral diseases were rare at both Townsville reefs. Coral cover has been increasing at Rib Reef since Cyclone Yasi (2011) and was high in 2014 (30-40%).

Coral bleaching was observed during scuba search surveys at both Townsville reefs (Table 5). Bleaching at Rib Reef was particularly noticeable (6-10% of total hard coral cover) because one of the coral genera that is most sensitive to bleaching, Seriatopora spp., was relatively abundant. Virtually all colonies of Seriatopora spp. were affected by bleaching, though the degree of bleaching varied from pale colonies to recently dead colonies. Individual colonies from a variety of other coral genera were also affected. Bleaching at John Brewer Reef was similar: the majority of Seriatopora spp. were affected along with individual colonies from a variety of other genera. However, the overall proportion of bleached coral colonies was lower (1-5%) than at Rib Reef because Seriatopora spp. were less abundant. More reefs in the Townsville sector remain to be surveyed in 2015.

Table 4. Summary of results of scuba search surveys of reefs in the Townsville sector.

M=mid, WS = White Syndrome, BBD = Black Band Disease, BrB = Brown Band Disease, SEB = Skeletal Eroding Band Disease.

Table 5. Summary of coral bleaching observations for reefs in the Townsville sector.