Community and trophic structure of sea stars (Echinodermata: Asteroidea) in rocky reefs of Loreto, Gulf of California, Mexico

Abstract

Sea stars (Asteroidea) are invertebrates with remarkable importance in rocky and coral habitats as they occupy several levels in trophic webs, and many times act as top predators in these ecosystems. The taxonomic and biogeographic knowledge about this group in México is adequate, but there is still limited information on the ecology and functioning of its assemblages. The objective of this study was to compare the community and trophic structure of rocky bottom asteroids in two regions of the Gulf of California: Loreto and Ligüi (25.5° to 26.5°N). Individuals were censused in belt transects 25 × 2 m (N = 106, at depths from 3 to 12 m), abundance, species richness, diversity (H´) and evenness (J´) was estimated, as well as the number of seastars per trophic guild (carnivores, herbivores and detritivores), and of guilds present per transect. The results indicate that starfish assemblages in both zones were dominated by the species Phataria unifascialis, and that Loreto had significantly higher richness, abundance and diversity of asteroids than Ligüi,probably as a consequence of higher number of habitats and food resources. In relation to the trophic composition, in both areas herbivores predominated, followed by detritivores and finally by carnivores. Abundance in each trophic level was statistically higher in Loreto, and also there were more trophic groups per transect at that location.