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

Manta tow surveys were completed on eight reefs in the Capricorn-Bunker sector, four reefs in the Swain sector and two in the Pompey 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 the same reefs. Preliminary results of the manta tow and SCUBA search surveys are presented in this report.

Median reef-wide live coral cover declined on the majority of sampled reefs since previous surveys. Coral cover declined on six reefs in the Capricorn-Bunkers and on two reefs in the Swains and remained stable on two other reefs in each sector. Coral cover declined at both reefs in the Pompey sector. The declines in hard coral cover in the Swain and Pompey sectors 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 Cyclone Hamish in 2009. The manta tow results are summarised in Tables 1, 3 and 5.

Six crown-of-thorns starfish (COTS) were recorded during manta tow surveys on three reefs in the Capricorn-Bunkers, whilst three COTS were recorded during SCUBA searches at Fairfax Reef. This is the second successive survey where COTS have been recorded on this reef since it was first surveyed in 1991. One COTS was recorded at Wade Reef in the Swains during manta tow surveys but none were recorded on any reefs in this sector during the intensive SCUBA search surveys. Five COTS were recorded at Reef 21-064 in the Pompey sector during manta tow surveys and eight more were recorded at this reef during SCUBA search surveys. On reefs surveyed in the Capricorn-Bunkers, with the exception of Erskine and Fairfax Reefs, the incidence of "white syndrome" (a disease-like necrosis found particularly on tabulate Acropora spp.) had declined since 2007. The incidence of white syndrome increased slightly at three reefs in the Swains but had declined at a fourth reef. The incidence of White syndrome had declined at both reefs in the Pompey sector. The SCUBA search results are summarised in Tables 2, 4 and 6.

Evidence of bleaching was minimal: a few individual pallid colonies were seen on manta tow surveys of the back-reef areas of Lady Musgrave and Hoskyn Island Reefs and on the front of Broomfield Reef in the Capricorn-Bunker sector. A few pale colonies of Seriatopora hystrix were recorded in SCUBA searches at North Reef in the Capricorn-Bunker group and a few pale Fungiids (mushroom corals) were recorded at Reef 20-353 in the Pompey sector.

Perimeters of eight reefs were surveyed using manta tow (Table 1). Three sites on each of these reefs were then surveyed in detail using SCUBA (Table 2). During manta tows surveys six COTS were observed on three reefs, Boult, Fairfax and Lady Musgrave, although densities were below outbreak levels and all reefs in this sector have been classified as No Outbreak. Detailed surveys revealed only three COTS on a single reef, Fairfax Reef, although these numbers were also below outbreak levels. This contrasts with the last survey in 2008 when no COTS were seen on any reef in the Capricorn-Bunker sector. No outbreaks have been recorded from this sector over the entire history of survey by AIMS.

Since the last surveys in 2008, median reef-wide live coral cover (Table 1) has declined on six reefs (Boult, Erskine, Fairfax, Hoskyn, Lady Musgrave and North Reefs) and has remained stable on two others (Masthead Island, Broomfield). The declines on these reefs were due to a combination of large storms in 2008, which dramatically reduced cover, and Cyclone Hamish in 2009, which then further reduced cover to its present level.

SCUBA searches on the intensive survey sites showed that white syndrome disease was encountered on all reefs in this sector. However, the numbers of affected colonies were lower than the previous surveys in 2008, though this was mainly a result of the decline in hard coral cover; particularly table Acropora colonies that are notably susceptible to this disease. Brown band disease affected low to moderate numbers of colonies on most reefs, whilst skeletal eroding band disease was seen on low numbers of colonies on Masthead Reef.

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

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:

Perimeters of four reefs were surveyed using manta tow (Table 3). Three sites on each of these reefs were then surveyed in detail using SCUBA (Table 4). One COTS was recorded at Wade Reef in the Swains during manta tow surveys, but none were recorded on any reefs in this sector during the intensive SCUBA search surveys. This suggests that the COTS outbreaks that occurred during the early part of the decade have run their course and that the affected reefs are beginning to recover.

Median reef-wide live coral cover declined at two reefs, 21-550 and 22-084, but remained stable on the other reefs in this sector (Table 3). Cover at Reef 22-084 decreased from a moderate (10-20%) level to the very low (1-5%) level since the last survey in 2008. Reef 21-550 declined from high levels (30-50%) to moderate (10-20%) since 2008. These declines are most likely attributable to the effects of severe cyclone Hamish in March 2009. The two reefs that showed little change in coral cover also felt the effects of Hamish. However areas on these reefs exposed to strong wave action (back reefs) already had a low coral cover as a result of past recent COTS outbreaks.

SCUBA searches on the intensive survey sites showed that white syndrome disease was encountered on all reefs in this sector. Compared to surveys in 2008, the number of infected colonies had increased on three of the reefs, but declined on the remaining reef (Wade). Brown band disease occurred in low to moderate numbers of colonies only on Wade and Chinaman Reefs, whilst skeletal eroding band disease occurred in low numbers of colonies on all reefs except Reef 21-550.

Table 4. Summary of SCUBA search survey results for the Capricorn-Bunker sector.

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

Two reef perimeters were surveyed using manta tow (Table 5). Three sites on each of these reefs were then surveyed in detail using SCUBA (Table 6). Five COTS were recorded at a single reef, Reef 21-064, in the Pompeys during manta tow surveys, and eight were recorded at this reef during the detailed SCUBA search surveys. This reef has now been designated as undergoing an Incipient Outbreak. COTS in these numbers (~ 53 COTS/hectare) would be expected to have a local impact on live coral cover and are a cause for concern. No COTS were recorded at Reef 20-353 during either manta or SCUBA surveys.

Median reef-wide live coral cover declined on both reefs surveyed. Reef 22-353 declined from high levels (30 to 50%) in 2008 to very low levels (0 to 10%) in this survey. Reef 21-064 declined from high (30 to 50%) to moderate levels (10-30%). These declines are most likely attributable to the effects of severe cyclone Hamish in March 2009 as both reefs lie near to the path of the cyclone track. However, Reef 21-064 was further away (30km compared to 10km for Reef 22-353) and somewhat more protected which accounts for the smaller decline in coral cover.

SCUBA searches on the intensive survey sites showed that white syndrome disease was encountered on both reefs in this sector, but in very low numbers. The number of colonies infected decreased on both reefs compared to surveys in 2008. No Black or Brown Band disease occurred on either reef, whilst skeletal eroding band disease occurred in low numbers of colonies on Reef 21-064 only.

Table 6. Summary of SCUBA search survey results for the Pompey sector.　

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

References

English, S., Wilkinson, C. and Baker, V. (1997) Survey Manual for Tropical Marine Resources (2^nd Edition). Australian Institute of Marine Science. Townsville.

For further information contact
Dr. Hugh Sweatman, AIMS
Telephone: +61 7 4753 4470
Fax: +61 7 4753 4288
Email: h.sweatman@aims.gov.au