ltm2010-02-03

Dates: 19thFebruary - 2ndMarch 2010

Vessel: MV Iron Joy

Survey leader:

Kate Osborne

SummaryManta tow surveys were completed on seven reefs in the Pompey sector and three reefs in the Whitsunday sector of the Great Barrier Reef (GBR) Marine Park. Detailed surveys for benthic organisms, visual census of fishes and surveys for agents of coral mortality (SCUBA search) were made on eight reefs in the Pompey sector. Preliminary results from the manta tow and SCUBA search surveys are presented in this report.Median reef-wide live coral cover declined on all survey reefs in the Pompey sector. Several types of disturbance are likely to have contributed to the observed decline. With the exception of Penrith and Tern Islet, all reefs were located within 60km of the track of severe tropical cyclone Hamish a category 4 tropical rotating storm that passed through the region in March, 2009. Crown-of-thorns starfish (COTS) have been present on some reefs in sufficient numbers to cause coral decline and there was also evidence of low-level coral bleaching throughout the sector. Coral cover on three mid-shelf reefs in the Whitsundays was unchanged since surveyed in 2009.

	Image 2. Median reef-wide live coral cover declined on all survey reefs in the Pompey sector located within 60km of the track of severe tropical cyclone Hamish a category 4 tropical rotating storm that passed through the region in March, 2009. Exposed parts of reefs had been nearly completely wiped clean of hard coral. Photo: AIMS LTMP.

COTS were recorded on four reefs in the Pompey sector. Tern Reef is still classified as Active Outbreak where 19 COTS were counted, a substantial reduction from 141 observed in the 2008 survey. Reef 21-060 had the largest decline in coral cover since it was last surveyed in 2006 (from 40-50% to 5-10%) and was classified as Incipient Outbreak with 11 COTS recorded in 2010. Reef 21-062 was not surveyed using manta tow, but outbreak densities of COTS were observed during SCUBA searches. Three COTS were counted on 20-348 but future increases in COTS are unlikely as coral cover is already low around the perimeter of this reef.Coral bleaching was observed on five of the seven reefs manta towed in the Pompey sector and two of three reefs in the Whitsunday sector. Many affected colonies were pale rather than fully bleached and were uncommon on most reefs generally confined to specific genera, especially Montipora spp. However, an estimated 10% of corals on some parts of Penrith and Tern Reefs were bleached; bleaching was proportionally higher on the reef flats than on the reef slopes and several coral genera were affected.Although reefs in the Pompey sector were near to the track of cyclone Hamish (March, 2009), the extent of damage was variable because the dense network of reefs meant that some areas on reefs were sheltered compared to others nearby that received the full force of the storm. Exposed sections of reef were commonly denuded of coral and colonized by coralline algae. Also the impact of cyclone Hamish on coral cover could not be estimated on all reefs because several reefs had been subject to COTS outbreaks since the last surveys. However on those reefs without a history COTS coral cover decreased, with the greatest declines recorded on those reefs within 30km of the eye of the cyclone.Coral diseases were recorded on all reefs. Only one reef, Pompey Reef (No1) had moderate levels of disease. The full complement of identifiable diseases were recorded during from reefs in the Pompey sector during SCUBA searches (Table 2).The number of Drupella increased on most reefs but no reefs had densities that were high enough to cause significant coral mortality.Details of the manta tow method can be found in the Standard Operational Procedure No. 1 AIMS Research - Crown-of-thorns Starfish and Coral Surveys - Standard Operational Procedure 8 ] or in the Survey Manual for Tropical Marine Resources (English et. al.1997). For a full explanation of the COTS outbreak terminology used in this report, refer to COTS under "Reef Issues" at the following web-page: AIMS Research - Reef Monitoring

Pompey Sector

Perimeters of seven reefs in the Pompey Sector were surveyed using manta tow (Table 1). These reefs plus one additional reef (21-062) were also surveyed in detail using SCUBA (Table 2).

Median reef-wide live coral cover declined on all survey reefs. Several types of disturbance are likely to have contributed to coral decline. With the exception of Penrith and Tern Islet, all reefs were located within the severe impact zone of cyclone Hamish (March, 2009). Also COTS have been present in sufficient numbers to cause coral decline on three reefs and there was evidence of bleaching throughout the sector .

COTS were recorded on three reefs during manta tow (20-348, 21-060 and Tern Reef) and on two reefs during SCUBA search (21-060 and 21-062).Tern Reef continued to be classified as Active Outbreak. A total of 19 COTS were seen on Tern Reef, a substantial reduction from the 141 recorded in 2008. Despite outbreak levels of COTS median coral cover remained moderate (20-30%) on this reef. The largest decline in coral cover was recorded on reef 21-060 (40-50% in 2006 compared to 5-10% in 2010); 11 COTS were recorded and the reef was reclassified as Incipient Outbreak. While COTS activity had increased on this reef the major cause of decline was due to the effects of cyclone Hamish (though COTS almost certainly would have contributed). Similarly reef 21-591 showed a decline in coral cover from 30-40% in 2008 to 20-30% in 2010. Reef 21-591 was classified as an Incipient Outbreak when last surveyed in 2008. No COTS were seen during surveys in 2010 and the reef has been reclassified as No Outbreak. While COTS are a likely contributing factor to the observed decline in coral cover the main driver of the decline were the physical effects of cyclone Hamish.

Coral bleaching was seen on five of the seven manta towed reefs. Bleached corals were uncommon and restricted to a few taxa, especially Montipora spp. However, an estimated 10% of corals on some parts of Penrith and Tern Reefs were bleached; bleaching was most common on the reef flats and several coral genera were affected.

SCUBA searches on the intensive survey sites indicated that physical damage was a common cause of coral mortality. This included cyclone damage such as toppling of large blocks of reef framework and rubble banks composed of coral fragments. More recent damage, including breakage of branching coral and displacement of tabulate colonies, was common on some sites. On those reefs without recent COTS outbreaks, reef-wide live coral cover decreased from 20-30% to 5-10% on Pompey No.1 reef and Pompey No.2 reef that were both within the severe impact zone of cyclone Hamish. Penrith Island reef that lay in the moderate impact zone further away from the track of Hamish exhibited a smaller reduction in coral cover coral cover from 40-30% in 2008 to 20-30% in 2010.

SCUBA searches also recorded coral mortality due to COTS on two reefs. COTS have been observed on the sites at reef 21-060 in each of three surveys since 2006; 5 COTS were counted in this survey. COTS were also present on reef 21-062 in densities that are expected to have a major impact on coral cover: 17 COTS were recorded on the belt transects and many more were observed in general area (Table 2).

Low levels of coral diseases were recorded on all reefs during SCUBA searches. Moderate levels of a range of diseases were recorded at one reef: Pompey Reef No.1 (Table 2). The number of Drupella spp. increased on most reefs, but in no cases were densities sufficient to cause significant coral mortality.

SCUBA searches also detected low levels of bleaching on 7 of 8 reefs surveyed. Bleaching was restricted to small numbers of individual colonies. On Penrith Reef, Tern Reef and Reef 20-348, bleached corals were observed on 1 in 4 transects.

Table 1. Summary of results from manta tow surveys the Pompey sector.

Table 2. Summary of results of SCUBA search surveys in the Pompey sector.

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

Whitsundays

The perimeters of three reefs were surveyed using manta tow (Table 3). Reef-wide median live coral cover was unchanged since surveys in 2009.There were a few bleached coral colonies on the reef slope of Reefs 20-204 and 19-131. No evidence of COTS was seen. White syndrome diseases were common on the flank of Reef 19-131.

Table 3. Summary of results from manta tow surveys the Whitsunday sector.

References

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

 

This project is partially supported by the Marine and Tropical Sciences Research Facility

Dr. Hugh Sweatman , AIMS

Telephone: +61 7 4753 4470

Fax: +61 7 4753 4288

Email: h.sweatman@aims.gov.au