Vol.:(0123456789) 1 3 Marine Biology (2019) 166:72 https://doi.org/10.1007/s00227-019-3515-3 ORIGINAL PAPER Two time losers: selective feeding by crown‑of‑thorns star fsh on corals most afected by successive coral‑bleaching episodes on western Australian coral reefs John K. Keesing 1,3  · Damian P. Thomson 1  · Michael D. E. Haywood 2  · Russell C. Babcock 2,3 Received: 21 August 2018 / Accepted: 15 April 2019 © Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract Successive, extensive bleaching events have reduced coral cover and altered species assemblages signifcantly in the Monte- bello 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 pertur- bation, there have been changes in the abundance and distribution of the coral eating crown-of-thorns starfsh, Acanthaster cf. solaris (to densities of up to 320 ha −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 difered between sites and was infuenced by their local abun- dance. This study demonstrates that where crown-of-thorns starfsh populations greatly exceed outbreak threshold densities of 10–15 ha −1 , they are likely to impact recovery of coral communities from bleaching events and exacerbate bleaching induced changes in assemblage structure. Introduction There have been documented reports of high population den- sities, or “outbreaks” of the crown-of-thorns starfsh Acan- thaster planci sensu lato, as early as 1912 and through the 1940s and 1950s, in Japan (Yasuda 2018). Since then, more widespread awareness and reports of coral predation in the Red Sea, Australia and the north-western Pacifc (Chesher 1969) have resulted in outbreaks of crown-of-thorns starfsh becoming a major management issue on coral reefs. This phenomenon has been the topic of extensive research in the decades that have followed (see reviews by Moran 1986; Birkeland and Lucas 1990; Fabricius 2013; Pratchett et al. 2014). More recently, in the face of evidence that destructive outbreaks may at least partly have been caused by anthropo- genic impacts (e.g., nutrient enrichment; Brodie et al. 2005; Fabricius et al. 2010, or removal of predators; Sweatman 2008), active management intervention through attempting control programs have been instigated on Australia’s Great Barrier Reef (GBR) (Pratchett et al. 2014) and have been practiced in Japan for many years (Yamaguchi 1986; Naka- mura et al. 2014; Yasuda 2018). Although not as well known, occasional population fuc- tuations of crown-of thorns starfsh Acanthaster cf. solaris have been reported in the Pilbara region of north-western Australia since the 1970s (Wilson 1972; Wilson and Marsh 1974, 1975; Wilson and Stoddart 1987; Johnson and Stod- dart 1988; Marsh 2000a). With the exception of small but heavily industrialised areas of the coastline, the area does Responsible Editor: M. Byrne. Reviewed by K. Wolfe and N. Yasuda. * John K. Keesing john.keesing@csiro.au 1 CSIRO Oceans and Atmosphere, Indian Ocean Maine Research Centre, M097, 35 Stirling Highway, Crawley 6009, Australia 2 CSIRO Oceans and Atmosphere, Brisbane, GPO Box 2583, Brisbane, QLD 4001, Australia 3 University of Western Australia Oceans Institute, Indian Ocean Marine Research Centre, M097, 35 Stirling Highway, Crawley 6009, Australia