Localised high-density population of a sea cucumber on a Malaysian coral reef

Abstract

While tropical sea cucumbers are among the most conspicuous mobile invertebrates on coral reefs, information on their population biology and ecology is limited, particularly for dendrochirotids (suspension feeders). Here, we characterised a localised high-density population of the small and poorly described dendrochirotid, Colochirus quadrangularis, on a coral reef around Pom Pom Island, Malaysia. The high-density population was restricted to one site (Lobster Wall) on the south-eastern edge of Pom Pom Reef, with only 16 individuals found across all other sites. Average densities of this species were 669 ± 76 ind m−2 in the population epicentre, with a maximum of 1444 ind m−2, and mean body length across the population of 2.78 cm (SD ± 0.87). Colochirus quadrangularis showed preference for consolidated dead coral substrate while avoiding live corals. Asexual reproduction (transverse fission) was observed for the first time in this species along with cases of novel species interactions. There are no prior data for this species around Pom Pom Island, or elsewhere, to determine the drivers and impacts of this high-density Colochirus population, but these holothuroids may be an indication of the shifts in community states that can be expected for future coral reefs.