Living in the front: Neomysis americana (Mysidacea) in the Río de la Plata estuary, Argentina-Uruguay.

SCHIARITI A.; BERASATEGUI A. D.; GIBERTO D. A.; GUERRERO, R. A.; ACHA E. M.; MIANZAN H. W.

MARINE BIOLOGY

Año: 2006 vol. 149 p. 483 - 489

0025-3162

The Río de la Plata is one of the main estuarine systems of South America. It is characterized by a salt wedge regime, a well developed bottom salinity front, and a maximum turbidity zone (MTZ) associated to it. We described for the first time the spatial distributional patterns of Neomysis americana, the most abundant mysid and the main food item for juvenile fishes in this estuary. We analysed the link between mysid distribution and abundance and the bottom salinity gradient. A total of 242 plankton samples were taken from the Río de la Plata estuary in spring and fall between 1991 and 2001. Bottom salinity gradient was quantified from grids created on the basis of 348 oceanographic stations. N. americana population was characterised by high abundances (up to 2500 ind. m-3) and the presence of juveniles, males, gravid and non-gravid females in both spring and fall of different years. N. americana distribution tracks the position of the bottom salinity front, in different years and seasons. A Pearson’s correlation analysis between mysid abundance and bottom salinity gradient confirmed the spatial overlapping observed between the bottom salinity front (maximum salinity gradient) and mysid distribution. No correlation was detected between mysid abundance and bottom salinity (neither in spring nor in fall). We speculate that mysids concentrated at the frontal interface could take advantage of the high concentration of detrital material for feeding, and/or the high phytoplankton abundances that occur immediately offshore the front. Our results show that not only salinity may be important in setting distribution and abundance of etuarine mysids, but also the magnitude of the salinity gradient.