Another diner sits at the banquet: evidence of a possible population outbreak of Culcita sp. (Agassiz, 1836) in Maldives

Abstract

The cushion seastars Culcita spp. are facultative corallivores that can feed on different coral species. In Maldives, they showed general preference for small coral colonies and recruits belonging to the genera Pocillopora and Pavona (Montalbetti et al. 2019). Contrary to what has been described for the most investigated coral predator Acanthaster spp., large population densities of Culcita spp. have never been recorded to date, since the cushion seastar abundances have been reported to be less than 0.5 individuals per 100 m 2 on average, although these numbers can slightly vary from one place to another (Bruckner and Coward 2018). However, during different surveys performed from May to October 2018 in Faafu Atoll, Republic of Maldives, an unusual high density of cushion seastars was observed. Three belt-transects of 50 m x 4 m were performed on each reef in order to count the number of specimens within a unit area. In particular, a density of 42 seastars per 600 m 2 , thus meaning 1 specimen every 14.3 m 2 , was observed on the reef flat (~ 1 m depth) of Magoodhoo (Fig. 1A), an inhabited island located on the southeastern region of the atoll rim whose reef is approximately Fig. 1 (A) View of three specimens of Culcita sp. grouped together (indicated by black arrows) found on a reef flat in Magoodhoo island. Scale bar 15 cm. (B) Detail of two individuals found close to eaten coral colonies (indicated by white arrows). Scale bar 5 cm.