Distinct Size and Distribution Patterns of the Sand-sifting Sea Star, Archaster typicus, in an Urbanised Marine Environment.

Yong Kit Samuel Chan, Tai Chong Toh, and Danwei Huang (2018) Archaster typicus is a microphagous sea star ubiquitous throughout sandy shoals of the Indo-Pacific. Along highly urbanised coasts, loss of sandy habitats through land reclamation and degradation of adjacent mangrove forests and seagrass meadows, which serve as nurseries for A. typicus, could lead to local extinction of this species. To determine the population status of A. typicus in Singapore, we performed belt-transect surveys at three modified shores, then compared size structure, clustering patterns and ontogenetic shifts within the Central Indo-Pacific region. We found that A. typicus individuals were, among other things, larger in Singapore (79.2 ± 14.2 mm) than the rest of the Central Indo-Pacific region with further differences amongst Singapore's sites. Sea stars of this species were also greatly clustered in smaller areas within the transects, with most transects presenting small Nearest Neighbour Index values of < 1. While ontogenetic shifts were noted in previous studies, no juveniles have been recorded in the nursery habitats of mangroves and seagrasses, with limited size and mating seasonalities. Although A. typicus appears to have grown in size considerably on reclaimed beaches in Singapore, the lack of any apparent ontogenetic connectivity here may threaten the sea star populations in the near future, particularly in the context of growing coastal development in Southeast Asia.