Endobiont fauna of Porifera collected in the shelf-break frontal area of the Argentine Sea. Preliminary results on Mycale magellanica (Ridley, 1881)

L. SCHEJTER; CHIESA I.L.; DOTI, B.L.; GIBERTO. D.; BREMEC. C.

Girona, España

Congreso; VIII World Sponge Conference; 2010

Centre D'Estudis Avançats de Blanes

Literature about sponge endobionts and other associate species is very extensive. Many studies and reviews have shown the ecological, biochemical and physiological impact of these associations that could be sometimes species-specific. According to other studies in different regions of the world, polychaetes and amphipods are the most common endosymbionts. The type of endobionts and the species hosted are a function of both, morphology of the sponge and biotic interactions, but apparently no relationship was found considering abundances of endobionts and volume of the sponge. Endobionts obtain structural or chemical refuge, direct or indirect sources of food and sites for reproduction, among others.  Endofauna of many sponges from North Atlantic, Mediterranean, East Pacific and Antarctic waters was studied, but few species were studied in the SW Atlantic Ocean (i.e. Hymeniacidon sanguinea, Mycale (Aegropila) angulosa and Mycale microsigmatosa). In this study we present preliminary results on the endofauna of Mycale magellanica, one of the most widely distributed sponges in the Argentine Sea. Samples were obtained with trawling devices in four localities along the shelf-break front, at nearly 105m depth and between 39º 24’ S - 41º 51’ S and 55º 56`W – 58º 09’ W. Sponges were collected as part of the Patagonian scallop assemblage during stock assessment cruises. Consequently, due to this sampling procedure, specimens often were damaged and only the biggest pieces of M. magellanica were preserved for the present analysis. A total of 2.7 kg (six colonies between 340 g and 660 g) of wet material was dissected and examined under binocular microscope at laboratory and 846 individuals were sorted (average 350 individuals per kg). The number of taxa identified was 22. Crustaceans, mainly Amphipoda and Isopoda, reached between 66 and 90 % of the total number of specimens. The most abundant taxa were the amphipod Lysianassidae and the isopod Caecognatha sp. Other peracarids registered were Leucothoe sp., Seba cf. saundersii, Colomastix bastidai, Liljeborgia sp., Iathrippa sp., Fissarcturus sp. and Serolis schytei. We found juvenile stages and incubating females of some peracarids, what suggests their close relationship with M. magellanica. The rest of the endobiotic taxa were molluscs (mainly Hiatella meridionalis), echinoderms (Ophiactis asperula, Ophiura lymani, Ophiacanta vivipara and Pseudocnus dubiosus),   polychaetes (Spionidae, Polynoidae, Phyllodocidae) and the decapod Nauticaris magellanica. These results represent the first attempt to elucidate the composition of endobionts in sponges from the deep waters of the Argentine Sea. Mycale magellanica seems to be important in providing habitat for at least 22 species of small invertebrates, mainly crustaceans, in the study area. This is of particular interest considering the fishing effort exerted in the different Patagonian scallop banks there distributed, subjected to removal of benthic species. In this sense, sponges in general could contribute to enhance biodiversity in areas scarcely disturbed. This study was partially supported by INIDEP, CONICET, PICT 2007 2200 and PICT 2008 1119.