The importance of embayed coastal areas for the life cycle of two sympatric starfish species (Echinodermata, Asteroidea)

Abstract

Coastal embayed areas are important sites for many benthic and nektonic organisms that are being increasingly threatened by habitat degradation. The knowledge on the biology of these organisms can reveal the importance of such areas for their life cycles. Furthermore, population information is also imperative to recognize the importance of these species to structure coastal ecosystems and to provide support to management strategies. In this study, we aimed to evaluate the importance of a coastal embayment area for the generalist predator starfish Astropecten marginatus and Luidia senegalensis, analyzing their spatio-temporal distribution and populational parameters and evaluating whether (1) the species present a differential use of the area, (2) the species use the bay for recruitment, growth and reproduction and (3) there is an ontogenetic or gender related variation in the bay occupation. This study was carried out at Caraguatatuba Bay (SE Brazil), with monthly samples from July/03 to October/04. Although Astropecten was more abundant than Luidia, the two species had similar shifts in abundance, with peaks during cold/dry months, which are partly related to recruitment patterns. Species were distributed mainly towards the southern area of the bay, where A. marginatus had denser aggregations. Both species used the bay for recruitment, growth and reproduction. Males and females of both species occurred in similar numbers (sex ratio 1:1), except in late autumn (May-June) when females became more numerous. An annual reproductive cycle was observed for both species, with spawning occurring mainly in the rainy season, and recruitment mainly during fall/winter. Large individuals (>17 cm) of L. senegalensis were sub-represented in the bay, indicating possible adult migration to deeper areas, whereas A. marginatus had a more resident behavior. Distribution of both species correlated well with diet information previously available, with prey-partitioning suggested as a mechanism that allow their similar occupation of the area, and ontogenetic diet shifts explaining the adult migration of L. senegalensis. This highlights the relevance of feeding information to predict distribution of starfish. Our results elucidate the importance of the studied bay for the life cycle of these keystone species, elucidating species-specific vulnerabilities to coastal degradation and the importance of recognizing populational and distribution parameters in order to inform management policies.