Trophic ecology of the swimming crab Polybius henslowii Leach, 1820 in Galician and Cantabrian Seas: Influences of natural variability and the Prestige oil spill

Diet and feeding intensity of the portunid crab Polybius henslowii were studied during the spring of 2004 along Galician and Cantabrian continental shelves (NW Iberian Peninsula) between 78 and 287 m. The area had been affected by the Prestige oil spill in November 2002, with different sectors at different levels of pollution: highest in between Miño River and Cape Finisterre (MF) and from there to Estaca de Bares Point (FE) and lowest from Estaca to Cape Peñas (EP). From 37272 specimens collected in 59 bottom hauls, 342 were analysed for stomach fullness and diet composition. Stomach fullness was lower in FE, but with no significant differences among sectors. Diet was a mixture of pelagic and benthic prey: cephalopods (Ilex coindetti), brachyurans (P. henslowii) and polychaetes (Glycera sp.). Other prey were beloniform eggs and fish remains. Two stress markers were also studied in some specimens: Acetylcholinesterase (a neurotoxicity marker) varied among sampled areas, while lipid peroxidation (an oxidative stress marker) did not. Changes in trophic variables, distribution and density were analysed in relation to depth, surface and bottom T, surface Chl a from satellite imagery and tar aggregate concentration in sediments. Along Galician and Cantabrian coasts prey availability, linked to productivity level, seems to be the main factor affecting P. henslowii diet and distribution. Interannual abundance variability seems to be controlled by large-scale climatic conditions (NAO index). This natural variability masks possible effects induced by the oil spill.