Ascidians (Tunicata, Ascidiacea) collected during the LAMPOS cruise along the Scotia Arc

TATIÁN M, J. ANTACLI Y R. SAHADE

Ushuaia, Tierra del Fuego

Simposio; IBMANT/ANDEEP International Symposium and Workshop; 2003

Centro Austral de Investigaciones Científicas (CADIC), Alfred Wegener Institute (AWI) y Universidad de Hamburgo

Abstract. Ascidians are benthic animals, whose presence is common in all seas. In Southern Oceans, the Polar Front determines, as in many organisms, strong barriers to the ascidian distribution. The Northern Magellan and Southern Antarctic regions separated by this barrier, could be linked by the Scotia Arc, as was pointed out by Monniot & Monniot (1983) who found a faunal gradient between these regions through the Scotia Arc. The knowledge on the species composition and endemisms are, nevertheless, limited to a fragmentary trawl samples. Our objective is to extend the knowledge about species composition and to establish affinities between the ascidian fauna at the different stations performed during the present cruise. Ascidians were collected by Agassiz (AGT) and bottom (GSN) trawls, at depths between 250-600 m, on different substrate types. Animals were relaxed in current seawater and later fixed in buffered formalin seawater 4%. Morphological features were analyzed under binocular and microscope, to identify the different species. The reproductive status of colonial species was taken in account, recording the presence of tadpoles. Photographs were taken on living animals using a digital camera, to document the coloration, which is usually lost alter fixation. A total of 25 species were found along the different stations sampled during the cruise, being solitary species lighter abundant. Two species are new for the science, whereas 8 species were collected in new localities, extending their known area of distribution. Ascidian was a very common group in the gears, being present in more than 80% of the captures. A total of 10 families were found, being the more abundant Polyclinidae (5 species), Polycitoridae, Styelidae and Pyuridae (4 species). Associations between, or with, other benthic groups were found, as those of incrusting Didemnidae on sponges and bryozoans or the epibiosis by small ascidian specimens on the tunic of large Styelidae. Muddy bottoms supported higher species richness than hard bottoms, like gravel, pebbles, and volcanic stones. South Georgia Islands are the northward distribution limit for some Antarctic species, like Pyura discoveryi and Molgula pedunculata and also, an area of endemisms, like the species Pyura georgiana. Some geographic considerations can be stressed in relation to the ascidian distribution (e.g., some affinities between South Georgia with South Orkney and South Shetland, or the separation of the South Sandwich stations). Nevertheless, analyses done on species and stations revealed also influence of substrate type, which could overwhelm the geographic discussion.