Physical-Biological Interactions In The Abundance Of The Opossum Shrimp Neomysis Americana In The Bahía Blanca Estuary (Argentina)

GARIBOTTI, E.; CERVELLINI, P. M.; PICCOLO M. C.

Fox Iguazu, Brazil

Otro; American Geophysical Union. AGU Meeting of the Americas; 2010

American Geophysical Union

Mysids frequently dominated zooplankton biomass in shallow waters of estuaries. Neomysis americana has a strong diel, tidally modulated migration. Its shows spectacular ability to aggregate in bottom-water salinity fronts of estuaries. Recently, their migrations have been implicated as an important factor in sediment dynamics. In the Bahia Blanca Estuary studies of only spatial and temporal distribution of this species have been done, but they were not related to the tidal circulation and dynamics of the estuary. Mesozooplankton samples were collected at a station situated on the Canal Principal of the estuary with 200 µm nets during two tidal cycles, every 3 hours once each season of the year (Nov. 2007-Aug. 2008). Samples were taken at surface, mid-depth and near bottom. Towing was done against the water flow during five minutes (4.5 km/h). Physicochemical and meteorological parameters were also measured simultaneously. The species was only found in the spring season samples indicating a strong seasonality behavior. The abundance at the three water depths showed a characteristic distribution pattern. Near the bottom, the highest abundances were found during the daylight hours (138 ind/m3) and at midnight (02:00h) (117 ind/m3) as a consequence of the “midnight sinking” phenomenon. At mid-water level, maximum abundances were observed during sunset (93 ind/m3) and dawn (92 ind/m3), showing a characteristic ascent of the species. Whereas, near the surface abundances were the lowest showing peaks during nocturnal ascents (16 a 29 ind/m3). The mean depth at the station is 11 m, being the tidal range 3 m. PAR radiation under water fluctuated between 4.95 and 1153.47 µE/m s (