Geographie distribution of bryozoans in the Argentine Sea ( South-Western Atlantic )

Abstract

On the basis of benthos dredgings carried out by the R. V. Shinkai Maru on the Argentine continental shelf, the bryozoan associations and their areas of distribution were analysed. Presence/absence data of 95 species at 58 stations were processed using correspondence analysis. The area analysis confirms the classical zoogeographie scheme proposed by varions authors for our coasts: a Magellanic group occupying most of the studied area and another composed of stations from the Argentine biogeographie province, occupying the inner shelf off Buenos Aires and north Pata-gonian gulfs. According to our results, the limit between both assemblages is situated near the coast at approximately 43°S and offshore, at depths of 60-72 rn following a SW-NE direction. A graduai and progressive impoverishment in species number towards the north and towards inner sectors of the shelf is observed off Chubut and Buenos Aires. The transitional zone between both zoogeographie provinces is inhabited by species of wide distribution, adapted to support the fluctuating hydrolo-gical conditions that characterize this area. Even though the results of this study have shown a higher number of species in the Magellanic group, a comparison between the Magellanic and Argentine provinces cannot yet be made, since the Uruguayan and south Brazilian bryozoan fauna, also included in the latter, is mostly unknown.