BIOGEOGRAPHY AND CONNECTIVITY BETWEEN WESTERN SOUTH AMERICAN AND ANTARCTIC MARINE MOLLUSCS

Abstract

The latitudinal diversity gradient is widely recognized, leading researchers to assume that Antarctic fauna is impoverished. However, with increased sampling efforts, some studies have shown a great diversity of certain marine groups surrounding the Antarctic continent, with higher rates of them. Antarctic endemism may be associated with its isolation and climate change over the evolutionary time scale. Despite this relative isolation, recent evidence suggests some degree of connectivity between the Antarctic and South American faunas. Our study used secondary data extracted from Malacolog 4.1.1. The geographical area considered was the entire South American Atlantic coast and the the adjacent areas of the Antarctic (Antarctic Peninsula, part of the Weddell Sea and islands of the Scotia Arc). Our survey yielded 6517 species of molluscs. The most diverse province was the North Brazil Shelf, and the least diverse was the Scotia Sea. Endemism rates for low-latitude provinces were close to 15%, in contrast to the highest endemism rate of 40% in the Scotia Sea Province. The highest value for richness was found for the Guianan ecoregion, and the lowest value for the Antarctic Peninsula. Most ecoregions had an endemism rate around 3%, with the highest endemism in South Georgia. The richness gradient increased toward lower latitudes. The cluster analysis for the malacofauna indicated four significant groups. The bathymetric Rapoport´s Rule showed the increase of bathymetric range toward higher-latitude ecoregions and whereas Bergmann´s Rule showed the opposite relationship. The higher richness at -25 o