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


Summary

  • Some reefs in this sector remain to be surveyed in this year

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

Figure 1: Map showing location of reefs in the Cairns 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 thirteen reefs in the Cairns sector of the Great Barrier Reef (GBR). Preliminary results of the manta tow surveys are presented in Tables 1 and 2. Sector-wide median hard coral cover remained similar to 2018, the lowest levels recorded in the history of this study (Table 1). Hard coral cover declined on nine reefs and remained stable on four reefs. Declines in hard coral cover were most likely the result of a combination of coral bleaching in 2016/2017 and COTS predation, although partitioning the relative contribution is difficult due to their co-occurrence. No COTS were observed on manta tow surveys in 2019.

Scuba surveys at fixed sites (eight reefs) and broad-scale manta tow surveys recorded low levels (0-1%) of coral bleaching on all reefs. Incidence of coral disease including white syndrome, black-band disease, brown-band disease and skeletal eroding band disease was rare at all reefs. Density of the corallivorous snail, Drupella spp., was elevated at Hastings reef (287 per hectare) and very low on the other reefs where scuba surveys were conducted.

*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).