Historical spatial patterns of benthic diversity in the Río de la Plata estuary and its oceanic front, Argentina-Uruguay (35-36S)

GIBERTO, D.A.; BREMEC, C.S.; CORTELEZZI, A.; RODRIGUES CAPITULO, A.; BRAZEIRO, A.

Oaxaca, México

Congreso; First DIVERSITAS Open Science Conference: Integrating biodiversity science for human well being; 2005

Historical spatial patterns of benthic diversity in the Río de la Plata estuary and its oceanic front, Argentina-Uruguay (35°-36°S)   Giberto, D. A.1, 2; Bremec, C. S. 1, 2; Cortelezzi, A. 3; Rodrigues Capitulo, A. 1, 3; Brazeiro, A4   1. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina. 2. Lab. de Bentos-Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP), Argentina. 3. Instituto de Limnología “Dr. Raul A. Ringuelet” (ILPLA), Argentina. 4. Universidad de la República-Facultad de Ciencias. Uruguay.   ABSTRACT   Background and Goal of Study The Río de la Plata system is subjected to increasing anthropogenic impact, i.e. commercial fisheries. Many demersal fishes feed on benthic invertebrates, however the spatial and structural patterns of subtidal benthos are scarcely known. The main goal of this study is to identify major richness patterns of benthic assemblages from a large unknown system including freshwater, estuarine and marine environments (~50.000km2). Materials and Methods Spatial patterns were analyzed using multivariate analysis (CLUSTER, MDS and SIMPER analysis) applied to 200 sampling stations collected between 1984 and 2002. Species richness was utilized as a measure of diversity. Results and Discussion A total of 428 species and 18 taxa were found, with a dominance of mollusks (121 species), polychaetes (99), and crustaceans (91). Four main assemblages (A) were defined: A1 (freshwater and mixohaline sites, 44 species), A2 (mixohaline and marine sites <25m, 150 species), A3 (marine waters, 25-50m, 268 species), and A4 (marine waters, 50-250m, 105 species). Alpha diversity ranged from 1 to 65 species, with A1 displaying less variable species number and the higher number of exclusive species (63.64%). A2 and A3 shared the highest number of species. High diverse assemblages were mussel beds and those inhabiting coarse-sandy bottoms. Muddy bottoms were characterized by widespread species, while scallops beds were characterized mainly by exclusive species. Conclusion As a general rule, the faunal pattern observed in the study area follows the gradual difference in salinity and bottom type, with areas of high richness corresponding to marine waters with heterogeneous bottoms. This must be interpreted with caution, since most of the studies analyzed cover marine areas between 50-100m, while mixohaline and freshwater areas are under represented. Proper monitoring plans are needed to obtain basic information that could be used in future conservation plans.