Two time losers: selective feeding by crown-of-thorns starfish on corals most affected by successive coral-bleaching episodes on western Australian coral reefs

Successive, extensive bleaching events have reduced coral cover and altered species assemblages significantly in the Montebello and Barrow Islands in north-western Australia. In particular, acroporid and pocilloporid populations were dramatically reduced, while poritid and faviid corals were less impacted and now dominate coral assemblages. Subsequent to this perturbation, there have been changes in the abundance and distribution of the coral eating crown-of-thorns starfish, Acanthaster cf. solaris (to densities of up to 320ha(-1)) that have had a further impact on coral communities selectively targeting the coral taxa most susceptible to bleaching, often referred to as climate change losers. The feeding selectivity of A. cf. solaris under post-bleaching conditions was studied to determine its likely impact on coral communities and coral recovery. We found that even when Acropora and Pocillopora were extremely rare, A. cf. solaris demonstrated a high level of selectivity for these genera, although they consumed non-preferred taxa such as poritid, faviid, and merulinid corals in greater numbers. The consumption of non-preferred genera and families of corals differed between sites and was influenced by their local abundance. This study demonstrates that where crown-of-thorns starfish populations greatly exceed outbreak threshold densities of 10-15ha(-1), they are likely to impact recovery of coral communities from bleaching events and exacerbate bleaching induced changes in assemblage structure.