ltm200911-12

Dates: 11thNovember - 1stDecember 2009

Vessel:Elizabeth E II

Survey leader:

Alistair Cheal

Summary

As part of the MTSRF "COTS early warning surveys" (Project 1.1.2) twenty-three reefs in the Cooktown-Lizard Island sector, thirteen reefs in the Cairns sector and three reefs in the Innisfail sector of the Great Barrier Reef were surveyed using manta tows. Detailed SCUBA surveys for benthic organisms, reef fishes and agents of coral mortality were also completed on five reefs in the Cairns sector and four reefs in the Innisfail sector. These latter reefs had been selected as part of a program to assess the effects of rezoning the GBRMP in 2004 on reefs in the Cairns-Innisfail region. Three reefs in the Innisfail sector remain to be surveyed by SCUBA as part of this program in the 2009/10 field season. Preliminary results of the manta tow surveys and SCUBA searches are presented in this report.

No outbreaks of crown-of-thorns starfish (COTS) were found but COTS were recorded in low numbers on nine of 23 reefs (39%) during manta tow surveys in the Cooktown-Lizard Island sector. COTS feeding scars were recorded on many of the survey reefs in this sector. Highest numbers of COTS per tow (0.09) were recorded at Lizard Island (similar low numbers were recorded on this reef at the last survey in 2007). However, COTS numbers have been slowly building in the Cooktown-Lizard Island sector since 2005. Average numbers of COTS are now similar to those that preceded the last wave of COTS outbreaks which began in this sector in 1995. Preferred coral prey for COTS is plentiful on the majority of reefs surveyed in the Cooktown-Lizard Island sector. Historically the last two (and likely a third) series of COTS outbreaks on the northern and central GBR appear to have originated in the Cooktown-Lizard Island sector. There is some evidence that successive recruitments, from small populations on a small number of reefs, build up over time and give rise to a primary outbreak that subsequently sets off a cascade of outbreaks southwards through the GBR. In this case we may be seeing the build up to Active Outbreak levels of COTS on reefs in the Cooktown-Lizard Island and Cairns sectors in coming years. No COTS were recorded during manta tow or SCUBA surveys in the Cairns and Innisfail sectors.

From manta tow and SCUBA surveys there was no evidence of major recent disturbances to coral communities in the three sectors. Hard coral cover on all but one of the reefs was generally similar to the last surveys, mostly at moderate (10-30%) levels. Hard coral cover at Pixie Reef in the Cairns sector had increased from moderate in 2006 to high (30-50%) in 2009. SCUBA searches on reefs in the Cairns and Innisfail sectors found that incidences of coral disease and numbers of Drupella spp. (coral feeding snails) were mostly low and/or within the range of previous records.

A summary of the results is presented in Tables 1 to 5. Locations of the reef surveyed are given in Appendix 1 to 3. A full list of survey reefs appears in the

Long-term Monitoring Status Report Number 8.(AIMS Research - Crown-of-thorns Starfish and Coral Surveys - Standard Operational Procedure 8). A full explanation of the COTS outbreak terminology used in this report can be found on the AIMS Reef Monitoring web site (see AIMS Research - Reef Monitoring). Direct links to analysed manta tow data gathered on each survey reef in this report can be found by clicking on the reef names in the tables below.Cooktown – Lizard IslandSector

Twenty-three reefs were surveyed by manta tow (Table 1) as part of the MTSRF "COTS early warning surveys" (Project 1.1.2). These included three inner-shelf reefs, 16 mid-shelf reefs (where COTS most often occur) and four outer-shelf reefs, spread along a broad latitudinal gradient (Appendix 1). COTS were recorded on nine of these reefs (39%, all midshelf reefs) during manta tows, and COTS feeding scars were seen on 15 reefs (65%). COTS sightings were widely spread within this sector; from the latitude of Cooktown to well north of Lizard Island (Appendix 1). COTS were only recorded in low numbers, so none of the reefs was classified as having Incipient or Active Outbreaks. Individual COTS were often cryptic, hiding in amongst the reef matrix, as is common when numbers are low and favored food ( Acropora spp. corals) is plentiful. Highest numbers of COTS per tow (0.09) were recorded at Lizard Island. Similar low numbers were recorded on this reef in 2007 and COTS have been regularly sighted at Lizard Island since early 2000 without evidence of an active outbreak. However, there has been a slow increase in COTS numbers within the Cooktown-Lizard sector since 2005 (Figure 1). Average numbers of COTS are now similar to those that preceded the last major GBR COTS outbreaks which began in this sector in 1995 and subsequently spread southward to the Cairns sector (Figure 1) and beyond. Given these data and the abundance of preferred coral prey (branching and tabulate Acropora corals) in this sector, there is a possibility that COTS numbers will rise to outbreak levels on some reefs in the foreseeable future.

Median reef-wide live hard coral cover on the 23 reefs that were surveyed by manta tow varied from low (5-10%) to high (30-50%) (Table 1) and had generally remained stable since each reef was last surveyed. Hard coral cover was mostly moderate (10%-30%). No SCUBA searches were made on any reefs surveyed in this sector.

Cairns

Sector

Thirteen reefs were surveyed by manta tow (Table 2) as part of the MTSRF "COTS early warning surveys" (Project 1.1.2). These included three-inner shelf reefs, eight mid-shelf reefs and two outer-shelf reefs, spread throughout the sector (Table 2, Appendix 2). No COTS were recorded and all reefs were classified as either Recovering from past COTS outbreaks or No Outbreak. Median reef-wide live hard coral cover on these 13 reefs was mostly moderate with four reefs having high (30-50%) cover and one having low (0-10%) cover (Table 2). Hard coral cover had generally remained stable since last surveyed. One exception was Pixie Reef, not far from Cairns (Appendix 2), where hard coral cover had increased from moderate in 2006 to a high level. Preferred coral prey for COTS, branching and tabulate Acropora spp., were generally abundant on this reef and others in this sector.

Five of the 13 reefs manta towed in this sector were also surveyed intensively using SCUBA. These reefs had been selected as part of a program to assess the effects of rezoning the GBRMP in 2004 on reefs in the Cairns-Innisfail region. SCUBA searches in the Cairns sector found that incidences of coral disease and numbers of Drupella spp. (coral feeding snails) were mostly low and/or similar to previous records (Table 3).

Innisfail

Sector

Three reefs were surveyed by manta tow. No COTS were recorded and median reef-wide live hard coral cover was low or moderate (Table 4). Hard coral cover had generally remained stable since last surveyed 2-3 years previous and all three reefs were classified as Recovering from past COTS outbreaks.

Three of the reefs manta towed in this sector and another one were also surveyed intensively using SCUBA. These reefs had been selected as part of a program to assess the effects of rezoning the GBRMP in 2004 on reefs in the Cairns-Innisfail region. SCUBA searches in the Innisfail sector found that incidences of coral disease and numbers of Drupella spp. (coral feeding snails) were mostly low and/or within the range of previous records (Table 5).

	Image 1.Coral cover remains stable on the majority of reefs surveyed with no signs of recent disturbance. In this photo delicate foliose corals can be seen growing on the front slope of Mackay Reef.Photo:AIMS LTMP
	Image 2.Low Islets Reef continues to recover from damage inflicted by COTS and a cyclone Rona in 1999 and at the time of survey median reef-wide live coral cover had reached historically high levels. What impact cyclone Olga had in January 2010 remains to be seen. Photo:AIMS LTMP

Figure 1. Average density of COTS per reef in the Cooktown/Lizard Island and Cairns sectors of the Great Barrier Reef from 1986 throughto 2010. Error bars represent Standard Errors.

Table 1. Summary of manta tow survey results for the Cooktown – Lizard Island sector.

Table 2. Summary of manta tow survey results for the Cairns sector.

Table 3. Summary of results of SCUBA searches on reefs in the Cairns sector.

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

Table 4. Summary of manta tow survey results for the Innisfail sector.

Table 5. Summary of results of SCUBA searches on reefs in the Innisfail sector.

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

Appendix 1. Reefs surveyed by manta tow in the Cooktown-Lizard sector.

Appendix 2. Reefs surveyed by manta tow (ringed) and SCUBA (black dot) in the Cairns sector.

Appendix 3. Reefs surveyed by manta tow (ringed) and SCUBA (black dot) in the Innisfail 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