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

Dates: 3^rd – 21^st March 2016

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 (henceforth coral cover) and abundance of the coral feeding crown-of-thorns starfish (COTS), Acanthaster planci, were completed on five mid-shelf reefs in the Pompey sector of the Great Barrier Reef (GBR) using the manta tow technique. In addition, intensive scuba surveys of benthic organisms and fishes, as well as scuba searches for agents of coral mortality, were completed on 11 mid-shelf reefs. Preliminary results of manta tow surveys and scuba searches are presented in this report.

Manta tow surveys found that coral cover was variable. Cover was high (30-50%) at one reef, moderate (10-30%) at two reefs and low (0-10%) at two reefs. Overall coral cover was at similar levels to previous surveys but had increased at two reefs and decreased at one reef. Crown-of-thorns starfish (COTS) were recorded on manta tow at three of five reefs. On two reefs COTS abundance had decreased compared with the previous survey, while COTS were recorded on the third reef for the first time since 1992. An Active Outbreak of COTS was recorded at Reef 21-062 for the third consecutive survey, Reef 21-064 was reclassified as Recovering and the other three reefs remained classified as no outbreak. Coral bleaching was recorded at all reefs during manta tow surveys but was generally restricted to scattered individual coral colonies and did not exceed 10% of total hard coral cover on any occasion.

Coral bleaching was also recorded at all scuba survey sites. A low level of coral bleaching was widespread and individual colonies of a range of coral genera were affected, particularly Montipora spp., Seriatopora spp., Porites spp. and a variety of corals from the family Faviidae. COTS were observed during the scuba surveys at two reefs. Numbers of individuals and numbers of scars had decreased compared with previous survey at these locations. A small number of COTS scars were recorded at four other reefs. White syndrome disease, brown-band disease and skeletal eroding band (SEB) were rare in the Pompey sector and black-band disease was not observed at scuba survey sites. The density of the coral-feeding snails Drupella spp. ranged from 13.3/ha to 453/ha.

Results are summarised in Tables 1 to 3. 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 five reefs in the Pompey sector were surveyed using manta tow (Table 1). Coral cover at Reef 20-348 increased from very low at the last survey to moderate (10-20%). COTS have not been recorded on manta tow at this reef for two consecutive surveys. An active outbreak of COTS was recorded at Reef 21-062, but the number of individuals observed on manta tow has declined substantially since 2008. However persistent COTS activity meant coral cover declined from the previous survey to a very low level (0-5%). A single individual COTS was observed on manta tow at Reef 21-064 where coral cover remained stable at a low level (5-10%). Reef 21-054 was reclassified from Active Outbreak in 2014 to Recovering in 2016. Coral cover at Reef 21-187 was moderate (10-20%), which is about the same as in the previous survey. Three COTS were recorded on manta tow surveys of Reef 21-187 the first record from that reef in 14 years. There were also many feeding scars which indicate the presence of cryptic individuals. Coral cover at Reef 21-139 had increased to a high level (30-50%) since the previous survey, and reached very high levels in some areas. No COTS recorded on manta tow at Reef 21-139.

There were signs of recent mechanical damage at a number of reefs in the Pompey sector (20-348, 21-062, and 21-064) which was probably due to Cyclone Marcia. This category 4 cyclone passed through this area in February 2015 and likely contributed to the lack of recovery in coral cover seen on these reefs.

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

Three sites at each of eleven reefs were surveyed in detail using scuba. Coral bleaching was observed at all sites on all survey reefs (Table 2). At most reefs coral bleaching was restricted to scattered colonies, reaching up to 5% bleaching on some transects. The maximum bleaching category recorded was 5-10% at Pompey Reef No. 1 and Tern Reef. The hard coral genera Montipora spp., Porites spp., Favia spp., Goniastrea spp. and Seriatopora spp. were consistently the most affected. Bleached soft corals were seen at Reef 21-591, Tern Islet and Penrith Island. Up to 20% of soft corals at Penrith Island Reef were bleached.

Table 2. Summary of coral bleaching at reefs in the Pompey sector. Coral genera are listed from most abundant to least abundant in terms of number of colonies affected. 15 transects were surveyed per reef.

# transects: represents number of transects with bleaching observed from the 15 transects surveys. Median and maximum: refer to values for the bleaching categories.

COTS were observed at two reefs during scuba search surveys (Table 3). Nine large adult COTS were recorded at Reef 21-062 as well as 37 COTS feeding scars. Individuals were noticeably flaccid, suggesting they were in poor condition, possibly due to the low coral cover. Six large adult COTS and one small sub-adult were recorded at Reef 21-064 and 28 feeding scars were seen. These numbers were similar to the previous surveys of these locations two years earlier. Both COTS and feeding scars were recorded at Reef 21-060 in the previous survey but none were observed this year’s survey. Coral disease was generally rare at survey sites in the Pompey sector, with a maximum record of 11 colonies with white syndrome at Reef 21-353. The highest density of Drupella spp. was 453/ha at Pompey Reef No. 2. Densities of this order are not unusual on reefs in this sector. At all other locations, the density of Drupella spp. was much lower and similar to the long-term average for these reefs.

Table 3. Summary of SCUBA search surveys for reefs in the Pompey sector.

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