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

Dates: 1^st September to 21^st September 2013

Vessel: RV Cape Ferguson

Survey leader: Ian Miller

Manta tow surveys for the 2014 survey year* were completed on eight reefs in the Capricorn-Bunker sector, and four reefs in the Swain sector of the Great Barrier Reef (GBR). Detailed surveys for benthic organisms, visual census of fishes and surveys for agents of coral mortality (scuba search) were made on all these reefs except for one reef in the Swain sector. Preliminary results of the manta tow and scuba search surveys are presented in this report.

Median reef-wide live coral cover had increased or remained at levels similar to those recorded during previous surveys in 2012* when hard coral cover on the majority of survey reefs was yet to recover from declines due to prior impacts from severe weather. The declines in hard coral cover in the Swain sector were attributed to Severe Tropical Cyclone Hamish in March 2009; declines in hard coral cover on Capricorn-Bunker reefs were due to the combined effects of a large storm in 2008 and Severe Cyclone Hamish in March 2009.

Crown-of-thorns starfish (COTS) numbers remain elevated on a number of reefs in the Capricorn-Bunker sector. There is still an Active Outbreak on Fairfax Reef, which has been active since 2012. COTS continue to increase in numbers on Lady Musgrave Island that remains classified as an Incipient Outbreak. Low numbers of COTS were also observed on Boult Reef. Small numbers of COTS, well below outbreak densities, were also recorded during manta tow surveys on Chinaman Reef in the Swain sector. Manta tow survey results are summarised in Tables 1 and 3.

No COTS were recorded during scuba search surveys on reefs in either the Swain or Capricorn-Bunker sectors. On all reefs surveyed, signs of coral disease, counts of Drupella spp. and coral bleaching were generally below those seen in previous surveys. The notable exceptions in the Capricorn-Bunker sector were; Erskine Reef and Masthead Reef that had higher than normal coral mortality due to Brown Band Disease; Masthead and North reef that had higher than normal coral mortality due to White Syndrome; Fairfax Reef that had elevated scarring due to unknown reasons. The exception in the Swain sector was Reef 22-084 that had higher than normal levels of white syndrome. The SCUBA search results are summarised in Tables 2 and 4.

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.

* Survey year reflects financial year of survey, for instance 2012 represents reefs surveyed between July 2011 and June 2012. Surveys for this current financial year are presented as 2014 despite surveys actually taking place in the 2013 calendar year.

Perimeters of eight reefs were surveyed using manta tow (Table 1). Three sites on each of these reefs were also surveyed in detail using scuba (Table 2). During manta tows surveys 43 COTS were observed on Fairfax Reef. This population was highly concentrated on the back reef area and constituted an ongoing Active Outbreak. The outbreak was first observed in 2012 and was the first Active Outbreak to be recorded using manta tow on any reef in this sector since the beginning of surveys in 1986. An Incipient Outbreak was also recorded on Lady Musgrave Island Reef. This is also an ongoing outbreak that was first observed on this reef in 2013. Similar to the outbreak on Fairfax Reef COTS were concentrated on the sheltered back reef area where coral cover was the highest. Small numbers of COTS, below outbreak levels, were also recorded on Boult Reef.

Reefs in this sector are characterised by their relatively low coral cover resulting from large storms in 2008 and Severe Cyclone Hamish, which passed some 100km to the east of the Capricorn-Bunker reef complex in March 2009. Since the last surveys in 2012, median reef-wide live coral cover on the majority of survey reefs in this sector has increased (Broomfield, Erskine, Hoskyn, Lady Musgrave, North) while remaining stable on the rest (Boult, Fairfax, Masthead) (Table 1). The increase in coral cover on the majority of reefs and the presence of many small coral colonies suggest that the prognosis for further recovery on these reefs remains good. No bleaching of hard corals was recorded during manta tow surveys of reefs in this sector in 2014.

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

Scuba searches on the intensive survey sites (Table 2) found white syndrome disease on all reefs in this sector except for Hoskyn Island Reef and Lady Musgrave Island Reef. On Masthead Reef and North Reef the incidence of white syndrome had increased from previous years. Similarly elevated numbers of unknown scars were recorded from Fairfax Island Reef compared to previous surveys. Brown band disease affected low to moderate numbers of colonies on most reefs with the exception of Masthead Reef and Erskine Reef where incidence of the disease was higher than seen in previous years. Skeletal eroding band disease was seen on low numbers of colonies on a minority of reefs. This higher than normal incidence of white syndrome, unknown scars and brown band disease on a number of reefs was surprising given that the reefs in this sector remain in the early stages of recovery and that the colonies affected were generally small. No COTS were observed during scuba searches and counts of Drupella spp. were generally below those recorded in previous years.

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

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

For more information on white syndrome refer to the AIMS web site at:

AIMS Long Term Monitoring - Coral Diseases on the Great Barrier Reef - Introduction

Perimeters of four reefs were surveyed using manta tow (Table 3). Three sites on each of these reefs except for Wade Reef were then surveyed in detail using scuba (Table 4). One COTS was recorded during manta tow surveys at Chinaman Reef, but none were recorded during the intensive scuba search surveys.

In general, patterns of change in coral cover on reefs in this region indicate recovery from recent declines due to Severe Cyclone Hamish that passed through the area in March 2009. Coral cover had increased on Reef 22-084, Chinaman and Wade while it remained stable on reef 21-550. No bleaching of hard corals was recorded during manta tow surveys of reefs in this sector in 2014.

Scuba searches on the intensive survey sites found white syndrome disease on all three reefs in this sector. Of those reefs where signs of white syndrome were observed Reef 22-084 had elevated levels of white syndrome compared to previous years. Low levels of brown band disease were recorded at two reefs (Reef 21-550 and Reef 22-084), whilst skeletal eroding band disease occurred at background levels on Reef 21-550 and Chinaman Reef. Drupella spp. were observed on all three reefs but at numbers that would not be considered exceptional.

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

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

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