Preliminary report on surveys of the Whitsundays sector of the Great Barrier Reef


Summary

·        8 Reefs were surveyed in the sector using fixed transects surveys.

·        4 reefs were surveyed using manta tow surveys.

·        First surveys since cyclone Debbie in 2017.

·        Sector wide coral cover was moderate.

·        No crown-of-thorns-starfish were recorded.

·        Coral bleaching was recorded at half the reefs surveyed, but at low levels (scattered, individual colonies) decreased from the previous survey.

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

Figure 1: Map showing location of reefs in the Whitsundays sector.

As part of the Long Term Monitoring Program (LTMP), manta tow surveys of hard coral cover and the abundance of the coral feeding crown-of-thorns starfish (COTS), Acanthaster cf. solaris* were completed on four reefs in the Whitsundays sector of the Great Barrier Reef (GBR). Preliminary results of the manta tow surveys are presented in Tables 1 and 2.

Based on the four reefs surveyed by manta tow, the sector-wide median hard coral cover was moderate (10-30%), and has remained stable since the previous surveys in 2017. The 2017 surveys were completed just before the passage of Severe Cyclone Debbie, which passed over the Whitsundays region intensifying to a category 4 system before making landfall near Airlie beach.

Two outer-shelf reefs increased in hard coral cover from 2017 levels, indicating limited impacts from Cyclone Debbie. In contrast, hard coral cover declined on two mid-shelf reefs most likely due to the passage of the cyclone. Manta tow surveys at 2 standard LTMP reefs (one mid-shelf and one outer-shelf) could not be completed due to rough weather, and manta tow surveys were not conducted on the inner shelf reefs due to poor visibility.

Scuba surveys at fixed transects on eight reefs recorded low levels of bleaching restricted to scattered individual colonies that was most likely the result of low cumulative heat stress over the preceding summer months. No COTS were recorded during either manta tow or fixed site surveys at any of the reefs. Counts of coral disease, include white syndrome, black band disease, brown band disease and skeletal eroding band disease were low during fixed site surveys at all reefs. Densities of the corallivorous snail Drupella spp., was low on all reefs. Analyses of hard coral cover and coral community composition from fixed site surveys on eight reefs is currently underway and will be reported once completed. This will allow a more confident estimate of the hard coral cover in this sector.

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).