POLYCHAETE DISTRIBUTION OF THE NEAR SHORE ZONE OF MARTEL INLET, ADMIRALTY BAY (KING GEORGE ISLAND - ANTARCTICA)
Bromberg, S. ; Nonato, E. F.; Corbisier, T. N. & Petti, M. A. V.
Instituto Oceanográfico da Universidade de São Paulo, Praça do Oceanográfico, 191, Cidade Universitária, 05508-900, São Paulo, SP, Brazil
The antarctic benthic communities are characterized by high level of endemism, as a result of speciation during long isolation periods and limited dispersal abilities of their pelagic larvae. Peculiarities such as highly seasonal light regime, long-term stability, extreme seasonality of food supply, freezing of the intertidal and upper sublittoral zone and other disturbances limit and direct the faunal distribution. As a consequence of the ice mechanical action, sessile benthic invertebrates are removed and replaced by pioneer species. The aim of this study is to investigate the structure of polychaete communities in Martel Inlet, looking for relationships with the type of bottom and with the ice effects. The present survey is part of the project "Bionomia da Fauna Bentônica Antártica" carried out by Instituto Oceanográfico da Universidade de São Paulo since 1988. The samples were taken in the summer of 1994/95 at four stations along a transect from 6 to 25 meters depth in front of the Brasilian Antarctic Station "Cmte Ferraz". Two additional stations were also established at 18 meters, in order to verify the ice-scouring effect on the communities. Five replicates per station were sampled with corers (10 cm diameter, 20 cm height) operated by SCUBA divers. The distribution of the polychaetes showed a defined zonation pattern as a function of depth, induced mainly by sedimentary differences and ice-scouring. The density of polychaetes increased with depth as verified averages of 30,6/78,54 cm2 (6 meters); 80,4/78,54 cm2 (11 meters); 143,2/78,54 cm2 (18 meters) and 247,2/78,54 cm2 (25 meters). In the ice-scouring area the densities were more variable. The preliminary analysis of the samples revealed the presence of nearly 13 families of polychaetes and the predominance of species of the families Cirratulidae, Spionidae and Maldanidae. Sedentary representatives of the families Sabellidae and Terebellidae were common in deeper areas where the ice mechanical influence is smaller. Nine species have been identified up to now: Ophryotrocha notialis, Microspio moorei, Brania rhopalophora, Ophelina syringopige, Apistobranchus gudrunae, Sphaerodorum parvum, Barrukia curviseta, Brada villosa and Aglaophamus ornatus.