Report on surveys of the Capricorn-Bunker and Swain sectors of the Great Barrier Reef

Dates: 8^th to 29^th August 2014

Vessel: RV Cape Ferguson

Survey leader: Mike Emslie

Manta tow surveys and scuba search surveys for benthic organisms, fishes and agents of coral mortality were completed on four reefs in the Capricorn-Bunker sector and five reefs in the Swain sector of the Great Barrier Reef (GBR). Preliminary results of manta tow and scuba searches are presented in this report.

Median reef-wide live coral cover was variable but mostly moderate (10 to 30%) in both sectors, with clear signs of recovery from the devastating and widespread effects of severe tropical cyclone Hamish in 2009. Coral cover was generally higher than was last reported at each reef. No crown-of-thorns starfish (COTS) were recorded during manta tow surveys in either the Capricorn-Bunker or Swain sector.

Scuba surveys found low incidences of coral disease in the Capricorn-Bunker sector and on three of the five reefs in the Swain sector, but incidences had increased on two reefs. The number of cases of White Syndrome coral disease at Gannett Cay Reef had doubled from previous year but was still low. The incidence of White Syndrome disease at East Cay was the highest yet recorded at that reef, and was substantially higher than the long-term average for GBR reefs in the same position on the continental shelf. Counts of Drupella spp. from scuba surveys were generally low or within the range of previous surveys in both the Capricorn-Bunker and Swain sectors. The large numbers of Drupella spp. recorded in 2013 at Gannett Cay had decreased, but were still high compared with the average for the GBR.

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]. For a full explanation of the COTS outbreak terminology used in this report refer to the following web-page: Crown-of-thorns on the Great Barrier Reef.

Perimeters of two reefs were surveyed using manta tow (Table 1). Sites on each these reefs plus two others were also surveyed in detail using scuba (Table 2). No COTS were recorded during manta tow surveys. Similarly, no COTS were recorded during scuba searches at any reef in the sector. Last year an Incipient Outbreak was recorded on Lady Musgrave Island, however rough weather meant that this reef could not be resurveyed. Similarly the Active Outbreak recorded last year at nearby Fairfax Island Reef is due for resurvey next financial year.

Median reef-wide live coral cover ranged from 40 to 50% on Broomfield Reef to 10-20% on Wreck Reef (Table 1). Coral cover has remained stable on Wreck Reef but has increased slightly since the last survey of Broomfield Reef. The variability in coral cover among reefs reflects differences in recovery from storms in 2008 and from Cyclone Hamish in 2009. Large numbers of coral recruits were observed at all reefs during scuba searches, suggesting that recovery in coral cover is well underway.

Scuba searches on the intensive survey sites found low occurrence of coral disease. For more information on coral disease refer to the AIMS web site at: AIMS Research – Coral Disease. Numbers of Drupella spp. were low to average based on GBR wide data (Table 2).

Table 1: Summary of manta tow survey results for the Capricorn-Bunker sector.

Table 2: Summary of SCUBA search survey results for the Capricorn-Bunker sector.

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

Perimeters of four reefs in the Swain sector were surveyed using manta tow (Table 3). Sites on each of these reefs plus one other were also surveyed in detail using scuba (Table 4). No COTS were recorded during manta tow surveys or during SCUBA search surveys at any reef.

Median reef-wide live coral cover was moderate (10 to 40%) on all four reefs: Reef 21-529, Gannet Cay, Turner Cay and Snake Reef, all of which suffered from major coral mortality from either Cyclone Hamish in 2009 or from COTS outbreaks prior to 2006 (Horseshoe Reef and Gannet Cay). Coral cover had increased on all these reefs, indicating strong recovery.

Table 3: Summary of manta tow survey results for the Swain sector.

Scuba searches at the intensive survey sites at East Cay in the Swain sector recorded the highest incidence of White Syndrome disease for this reef since scuba surveys began in the mid 1990’s. This level of disease is exceptional for a reef in this sector and has only been exceeded by that observed on Reef 21-529 in 2003. The incidence of White Syndrome disease on Gannet Cay and Snake Reef were also higher than the long term averages for GBR reefs in similar shelf positions (Table 4). However these levels of White Syndrome were not higher than those seen on either reef previously. Similarly the incidence of Brown Band disease and numbers of Drupella at Gannett Reef while higher than the long term average GBR were not exceptional for this reef. Incidence of White Syndrome and Brown Band disease on the other reefs were within the range of previous observations. Other diseases only occurred at low levels.

Table 4: Summary of SCUBA search survey results for the Swain sector.

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