Survey Report 15 February - 4 March 2012

Dates: 15^th February to 4^th March 2012

Vessel: MV Floreat

Survey leader: Alistair Cheal

Manta tow surveys were completed on seven reefs in the Cairns sector and seven reefs in the Innisfail 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 12 of these reefs. Preliminary results of the manta tow and scuba search surveys are presented in this report.

Median reef-wide live coral cover was variable but most often low in the Cairns sector; 5 to 10% on four reefs, 10-20% on two reefs and 20-30% on one reef. Coral cover at each reef was generally similar to that last reported in 2010 or 2011 although there was a tendency towards lower values on some reefs in recent surveys. This is likely due to peripheral effects of Cyclone Yasi that developed just prior to surveys of these reefs in February 2011. In the Innisfail sector median reef-wide live coral cover was low (<10%) on all seven reefs and similar to or lower than values last recorded in 2009 or 2010.

A single crown-of-thorns starfish (COTS) was recorded during manta tow surveys. This animal was observed at Green Island in the Cairns sector. No COTS were recorded during SCUBA searches. Manta tow survey results are summarised in Tables 1 and 3.

Low levels of partial and complete coral bleaching were recorded on reefs in both the Cairns and Innisfail sectors; typically <5% of hard corals were affected at each reef. The suite of species with bleaching was consistent among reefs and included genera known to be sensitive to thermal stress as well as some species with unknown sensitivity. Water temperatures on survey sites of up to 30°C were noted and detailed temperature profiles will be available from a temperature logger retrieved from Thetford Reef during surveys.

Incidences of coral disease in the Cairns sector were generally within the range of previous surveys but with the exception of one reef incidences of White Syndrome disease in the Innisfail sector were among the highest recorded since surveys began in 2006. Counts of Drupella spp. were generally low and within the range of previous surveys in both sectors. 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.

Cairns Sector

Perimeters of seven reefs were surveyed using manta tow (Table 1). Sites on five of these reefs were also surveyed in detail using scuba (Table 2).One COTS was recorded at Green Island during manta tow surveys but none were recorded on other reefs in this sector during manta tows or scuba searches.

Median reef-wide live coral cover was variable, being 5 to 10% on four reefs, 10-20% on two reefs and 20-30% on one reef (Table 1). In general, coral cover had remained relatively stable on reefs in this sector but with a tendency towards declines since last surveyed in 2010 or 2011. This was likely due to peripheral effects of Cyclone Yasi. This large cyclone that reached Category 5 was active off the north Queensland coast at the beginning of February 2011 and crossed the coast near Mission beach in the Innisfail sector on February 3^rd.

Although the strongest winds from Cyclone Yasi occurred south of the Cairns sector, these reefs still experienced extremely large seas and patchy coral damage was recorded on some reefs in LTM surveys immediately after the passage of Cyclone Yasi.

Table 1.Summary of manta tow survey results for the Cairns sector.

Scuba searches on the intensive survey sites showed little evidence that coral diseases had widely increased in this sector. Although incidences of white syndrome on some reefs were above GBR averages this has often been the case for reefs in the Cairns sector. The notable exception was Arlington Reef where the incidence of white syndrome (n = 27) was well above the previous maximum value recorded for this reef (n =9). Numbers of Drupella spp. were low to average based on GBR wide data (Table 2).

Low levels of bleaching of hard corals were observed during scuba searches on the majority of transects at each reef and during manta tows. Typically <5% of hard corals were estimated to be partially or completely bleached. The suite of species with bleaching was consistent among reefs and was most common among genera known to be sensitive to thermal stress such as Pocillopora, Seriatopora, Stylophora and Montipora. Some colonies of Montastrea curta and Goniastrea pectinata were also partially or completely bleached on most reefs, along with a small number of other Faviids and Porites spp. Bleaching was more severe at Green Island and Fitzroy Island where bleached Acropora spp. were also observed during manta tow surveys. Low levels of bleaching were also recorded during manta tow surveys with many tabulate Acropora spp. hard coral colonies having a characteristic lurid appearance as a precursor to bleaching. This was most often seen on back reef areas during surveys. Water temperatures generally ranged from 28 – 30°C during scuba searches at depths between six and 12m. A long-term temperature logger was retrieved from a reef slope site at Thetford Reef which should provide a profile of temperatures leading up to these bleaching observations.

Table 2.Summary of SCUBA search survey results for the Cairns sector.

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

For more information on coral disease refer to the AIMS web site at:

AIMS Research – Coral Disease.

Innisfail Sector

Perimeters of seven reefs in the Innisfail sector were surveyed using manta tow (Table 3). Fixed reef slope sites on each of these reefs were also surveyed in detail using scuba (Table 4). No COTS were recorded during manta tows or scuba search surveys.

Median reef-wide live coral cover was low (<10%) on all seven reefs and similar or slightly lower than values last recorded in 2009 (one reef) or 2010 (six reefs). On some of these reefs coral cover has been relatively low for over a decade due particularly to COTs outbreaks which began in the late 1990's and the nearby passage of Category 4 Cyclone Larry in 2006. Any effects of category 5 Cyclone Yasi in February 2011 were hard to discern in these latest surveys because coral cover was still low and cover of rubble was high as a result of previous disturbances. Even so, sections of some reefs did appear to have been broken up by waves from Cyclone Yasi.

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

Scuba searches on the intensive survey sites on reefs in the Innisfail sector found incidences of White Syndrome disease that were among the highest recorded on these reefs since surveys began in 2006. At all but one reef (McCulloch), incidence of white syndrome was higher than the mean value for reefs in that position on the continental shelf or for the GBR overall (Table 4). Given the low cover of hard coral in this sector, such increase in white syndrome disease could be significant. Other diseases only occurred at low levels and numbers of Drupella spp. were low to average based on GBR wide data (Table 4).

As in the Cairns sector, low levels of bleaching of hard corals were observed during scuba searches on the majority of transects at each reef, as well as during manta tows. Typically <5% of hard corals were estimated to be partially or completely bleached. The suite of species showing bleaching was consistent among reefs and was most common among genera known to be sensitive to thermal stress such as Pocillopora, Seriatopora, Stylophora and Montipora. Some Montastrea curta and Goniastrea pectinata colonies were also partially or completely bleached on most reefs along with a small number of other Faviids and Porites spp. Water temperatures ranged from 28 – 30°C during scuba searches at depths between six and 12m.

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

M = mid, O = outer, 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 (2ndEdition). Australian Institute of Marine Science. Townsville.

 

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

For further information contact

Dr. Hugh Sweatman , AIMS

Telephone: +61 7 4753 4470

Fax: +61 7 4753 4288

Email: h.sweatman@aims.gov.au