Broadscale survey of coral condition on the reefs of the Easter Group of the Houtman Abrolhos Islands

Anthropogenic activities that occur at the Abrolhos Islands include commercial lobster and line fishing and tourism. Impacts such as physical damage from diving, anchoring deployment of lobster pots and influence of land-based activities could cause changes to coral condition. The possible effects of human activities on coral reefs were noted as potential issues during management and stakeholder workshops (Fisheries WA 1998; Chubb et al. 2002; Webster et al. 2002). This survey broadly addressed potential impacts on the coral reefs by estimating coral cover, coral bleaching, coral disease, coral damage, and the abundance of the corallivores; Acanthasterplanci starfish and Drupella snails. Eight research sites were selected, including reefs in the Rat Island group, Suami Island group and Leo Island group and surveyed from the 16th to 21st of February 2004. At each site three 50 metre belt transects were videoed and a GPS reading taken at the start of each site. Transects were laid parallel to the reef crest at a depth of appropriately 4 - 6 m. The video transects were analysed using AVTAS (AIMS Video Analysis System), (Christie et al, 1996). The health of the corals 2 m either side of the transect line were examined and the following potential impacts assessed and quantified: Bleaching: The severity of bleaching on individual colonies and the proportion of colonies affected was estimated. Disease: Five categories of coral disease were recorded including, black band disease, white syndrome, skeletal eroding band, brown band and pink spot. The species infected and the number colony displaying disease symptoms were recorded. Corallivores: The levels of the damage and incidence of starfish and snails were counted at each site. Coral Damage: The extent and severity of coral damage was recorded.