OCCURRENCE OF PINNOTHERID CRABS (DECAPODA: BRACHYURA) IN MOLLUSK POPULATIONS OF SAN ANTONIO OESTE, PATAGONIA ARGENTINA.

OCAMPO, EMILIANO; NAHUEL E. FARIAS; NICOLÁS M. CHIARADIA; MAXIMILIANO CLEDÓN

Coquimbo-La Serena, Chile

Congreso; Mid-year meeting of the crustacean society; 2007

Universidad Católica del Norte, Chile.

Pinnotherid crabs are inhabitants of a wide variety of marine hosts. In Argentina most of the works on these crabs are limited to taxonomic discussions. More over there is little knowledge on their ecology worldwide. In order to asses the frequency changes in time of pinnotherid crabs in common mollusks of San Antonio Oeste, we compared an available dataset of 2003 with a new sampling of the gastropods Crepidula cachimilla, C. aculeata and the bivalve Atrina seminuda collected during April 2007. We found Calyptraeotheres garthi associated to Crepidula sp. and Tumidotheres maculatus to A. seminuda in both years. The occurrence frequencies were steady around 0.475 in A. seminuda. In C. cachimilla, it changed from 0.3 to 1. In the other hand, C. garthi was registered in C. aculeata for the first time. In 2004 it was possible to find C. cachimilla on every available hard substrate in groups of 2 to 10, while in 2007 it almost disappeared from the area. This drastic decrease is coincident with the new presence of C. garthi inside C. aculeata paleal chamber. These findings could be explained by a forced shift from a preferred host to a more frequent one.