Report on surveys of the Capricorn-Bunker sector of the Great Barrier Reef


Summary

  • Coral cover increased on three of four reefs surveyed in this sector.
  • Coral cover was high (>40%) on all reefs.
  • COTS numbers had increased to Incipient Outbreak level at one reef and to low numbers at another.

Hard Coral Cover 0-10% 10-30% 30-50% 50-75% 75-100%

Figure 1: Map showing location of reefs in the Capricorn-Bunker sector.

As part of the Long Term Monitoring Program (LTMP), manta tow surveys of coral cover and the abundance of the coral feeding crown-of-thorns starfish (COTS), Acanthaster cf. solaris* on four reefs in the Capricorn-Bunker sector of the Great Barrier Reef (GBR) were completed. Preliminary results of the manta tow surveys are presented in Tables 1 and 2. The overall median live coral cover for the sector was high (30 to 50%) and had increased since last surveyed (Table 1). Median reef-wide live coral cover (coral cover) had increased at three reefs: Broomfield, Lady Musgrave Is. and One Tree Is. (Table 2). There was a modest decrease in coral cover on one reef, Wreck Is., since 2017, although cover was still high. The cause of this decline is not clear. An increase in COTS numbers on Lady Musgrave Is. Reef to Incipient Outbreak levels had not prevented an increase in reef-wide coral cover as the COTS occurred in localized dense patches. Similar numbers of COTS have been recorded twice since 2013, suggesting that progression to an Active Outbreak will not necessarily occur. Very low numbers of COTS (three individuals) were recorded on One Tree Is. Reef for the first time since manta tow surveys began in 1986. The significance of this, if any, is not yet clear.

Scuba surveys of fixed transects recorded negligible coral bleaching; corals on only one of the 60 transects surveyed (15 per reef) were mildly affected. Cases of the coral disease white syndrome were moderately elevated on all reefs compared to recent years. The occurrence of brown band disease on Lady Musgrave Is. Reef was also higher. However, it is not uncommon for incidence of diseases to increase as coral cover reaches the high levels that were recorded. Occurrence of two other coral diseases (black-band and skeletal eroding band) was low. Numbers of the corallivorous snail, Drupella spp. were very low at all reefs.

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]. Further details of the monitoring program design, sampling methods and a full explanation of the A. solaris outbreak terminology can be found on the AIMS website.

*Note: genetic studies show that there are at least four species of COTS. These are the North and South Indian Ocean species (A. planci and A. mauritiensis), a Red Sea species (not yet named) and a Pacific species. The range of the Pacific includes the Great Barrier Reef and it has been provisionally named Acanthaster solaris (Haszprunar et. al. 2017).