The Southeast South American shelf large marine ecosystem : Evolution and components

The Southeast South American shelf large marine ecosystem (SSASLME) extends roughly over the entire continental shelf off southeastern South America, from 23° to 55°S, the largest shelf in the southern hemisphere. Distinctive bathymetry, hydrography, productivity and biological communities characterize this extensive marine ecosystem adjacent to Argentina, Uruguay and southeastern Brazil. The Falklands/Malvinas Current and Brazil Current are the major ocean flows in the SSASLME, and impose an eastern boundary to this ecosystem. While the former provides sub-tropical waters and organisms, the latter contributes elements of subantarctic origin. The encounter of these two currents with one another defines a Confluence Zone (CZ) of mixed waters which spans, on the average, from 25° to 45°S. Significant physicometeorological and biological processes described for the SSASLME depend upon the seasonal pattern of current intensification and latitudinal displacement of the CZ. Other oceanographic features, such as frontal zones, upwellings and low-salinity coastal waters, complicate the hydrological structure. Relevant finfish and invertebrate species of either commercial value or key ecological significance are distributed over a wide latitudinal range, which reveals the ecological extension of the SSASLME and the intimate connection between the sub-tropical and subantactic realms. Degradation of coastal water quality and anthropogenic perturbations to living marine resources are also significant throughout this system. The intensity of these stresses follows the pattern of distribution of human settlements, industriazilation, areas of resource exploitation and other coastal uses. These disturbances, extended both in time and space, concern areas under different jurisdictions. Compared to previous geopolitical partitions and regional arrangements, the LME perspective provides ecological arguments for the perception of the SSASLME as a functional unit for monitoring and management.