The turbidity front as a habitat for Acartia tonsa (Copepoda) in the Río de la Plata Estuary

DERISIO C.; BRAVERMAN, M.; GAITÁN, E.; HOZBOR C.; RAMÍREZ F.C.; CARRETO J.; BOTTO F.; GAGLIARDINI D.A.; ACHA E. M.; MIANZAN, H.

JOURNAL OF SEA RESEARCH

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2014 vol. 85 p. 197 - 204

1385-1101

Acartia tonsa is one the most abundant copepod species in estuaries worldwide. In the Río de la Plata estuary its highest densities seem to occur in an area of low quality food (detritus): the turbidity front (TF). The objective of this study was to understand how trophic and oceanographic drivers contribute to the highest densities of A. tonsa in the inner Plata estuary. The mean patterns of spatial distribution and density of this species were analyzed in relation to oceanographic and biological attributes of the estuary. Egg production rate (EPR) in the TF was evaluated as a measure of fitness and stable isotopes analysis indicated the possible sources of organic matter in its diet. This study confirmed that the highest densities of A. tonsa were mostly associated with the TF, where high suspended matter and low Chl-a occur. Immediately offshore of the TF, the copepod densities decreased and the maximum Chl-a values were found. Females close to the estuarine turbidity maximum (ETM) had lower EPR than those closer to the high Chl-a concentrations. In the TF, A. tonsa apparently fed on detritus close to the ETM and phytoplankton close to the edge of the TF. In this study it was discussed how retention processes, two layered flow and life history strategy of A. tonsa could be contributing to the development of the highest densities (more than 10,000 ind m-3) of this species in the inner estuary; despite of a poor quality food for development. A. tonsa can live and prosper in areas with high turbidity and low chlorophyll concentrations. These exemplify the plasticity of the species and help to understand the reasons to be a key species in many worldwide estuaries.