Porifera from the Argentine Sea: diversity in Patagonian scallop beds

The Patagonian scallop Zygochlamys patagonica (King & Broderip 1832) is distributed in the Magellanic Biogeographical Province. Its southern limit is Tierra del Fuego whereas the northern range extends to 42u S in the Pacific Ocean and to 35uS in the Atlantic Ocean (Waloszek 1984; Waloszek & Waloszek 1986; Ciocco et al. 1998). The commercial fishery started in 1996 in the Argentine continental shelf where it is performed by bottom otter trawls mainly at a depth range of 67–108m (Lasta & Bremec 1998; Gutie´rrez & Defeo 2003). Porifera are a frequently collected taxon in the invertebrate by-catch of the Patagonian scallop fishery (Bremec et al. 1998, 2000; Bremec & Lasta 2002). Sponges, being sessile and relatively fragile organisms, are very sensitive to pollution and mechanical stress produced by trawling (Muricy 1989; Wassenberg et al. 2002). Porifera from different Patagonian scallop beds in the Argentine Sea accounted for approximately 5–10% of total biomass of invertebrate by-catch during 1995, when commercial fishery started, and proved to be more sensitive to the fishing effort than other taxa (Bremec & Lasta 2002; Bremec et al. 2000). In these beds, the sponge contribution represented an average of 0.3 kg 100m22 (wet weight) between 1998 and 2001 (Schejter 2004). Consequently, studies on their diversity and distribution in areas subjected to trawling are important to assess the impact of fishery disturbances. Thirteen species of Demospongiae (four of which are new records for the Argentine Sea) have been identified, confirming the importance of this phylum as a major component of the scallop bed community.