Crown-of-thorns starfish promote additional fine-grained habitat fragmentation in a coral reef ecosystem

Abstract Context Species that provide habitat for other organisms are critical for land- and seascape structure. Since coral patch interiors offer different habitats and perform a functionally different role from edges, loss and fragmentation of corals can negatively impact biodiversity. Although processes leading to coral loss have been well documented, their impacts on habitat configuration (arrangement) are poorly documented and understood. Objectives We asked (1) whether Crown-of-thorns starfish (CoTS) forage preferentially on coral edges; and (2) whether they promote fragmentation by increasing the amount of edge habitat more than might be expected relative to random coral loss. Methods We used two different years (2012 and 2014, pre- and post-CoTS irruption) of classified photographic imagery from 10 × 10 m transects across 17 different coral reefs in Kimbe Bay, Papua New Guinea. Results Comparisons to standard neutral models at a grain of 15 cm showed that CoTS do not forage preferentially within or on the edges of coral patches. The fine-grained structure of coral patches in the seascape was substantially more fragmented post-CoTS, particularly at intermediate levels of coral cover. Coral cover declined by a relatively high mean of nearly 5% across all sites, with considerable variance in benthic habitat change between reefs. Conclusions CoTS are not preferential edge foragers at this scale of analysis. More broadly, our analysis shows how methods developed in terrestrial systems can offer insights into changes in seascape structure and provides useful detail for further research on the ecological impacts of CoTS on benthic fauna.