Mollusks from Southern South America, the Scotia Arc and the Antarctic Peninsula; Assessing Connectivity Among these Regions

The Southern Ocean has been intensively studied in recent decades with respect to the biogeography of marine invertebrates. Biological limitations, the geological history of Antarctica and South America, and oceanographic features of the Drake Passage potentially limit species connectivity between South America and the Antarctic Peninsula. However, there are many proposed occurrences of the same marine invertebrate species being found both in Antarctica and South America. This overlap of fauna has been explained by: (1) larval transport or drifting/rafting communities from one continent to the other, (2) the partly emergent Scotia Arc acting as a series of connective “stepping stones” or (3) poor taxonomy, i.e., cryptic species or poor identifications. None of these hypotheses has been systematically tested for benthic marine invertebrates. The present study assessed the presence of shared benthic mollusk species in Antarctica, South America, and the Scotia Arc by using species absence and presence in the area. Six percent of the Southern Ocean benthic mollusk biodiversity was shared between the three regions, and three quarters of these shared species showed signs of connectivity between 0 and 1000 m. Sixty five percent of the shared species were considered to show eurybathy (depth distribution broader than 1000 m depth ranges). This low, but not insignificant number of shared species from South American and the Antarctic Peninsula show signs of connectivity through the Scotia Arc, and that connectivity is mainly, but not exclusively achieved through the first 1000 m depth