Habitat effect on distribution and feeding of Ophidiaster ophidianus (Lmk.) (Asteroidea)

The purple starfish Ophidiaster ophidianus is an Atlanto-Mediterranean starfish protected under the EU’s Habitats Directive. Despite the wide distribution and the current range expansion of this warm affinity species in the northern Mediterranean areas, nothing is known about its diet. Using field observations and carbon (δ13C) and nitrogen (δ15N) stable isotopes, we explored possible changes in density and diet of O. ophidianus in relation to two different Mediterranean habitats: the coralline barren and the macro algae forest. Data were collected at the Marine Protected Area of Ustica Island (Southern Tyrrhenian Sea) from June to September 2009. Starfish density was not affected by the habitat, while on the contrary the diet of O. ophidianus was significantly different between barren and macro algae forest habitat. O. ophidianus fed mainly on crustose algae and bryozoans in barren, whereas it preferred the sponge Ircinia spp. in the forested habitat. Other food sources such as small gastropods and sedimentary organic matter were selected by this starfish. In general O. ophidianus showed a short niche breadth and omnivory habits with tendency to carnivory.