ABUNDANCE OF ACARTIA TONSA IN THE BAHIA BLANCA ESTUARY IN RELATION TO TIDAL AND THE DAY/NIGHT CYCLES

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

Bahía Blanca

Congreso; ECSA 44: SCIENCE AND MANAGEMENT OF ESTUARIES AND COASTS: A TALE OF TWO HEMISPHERES; 2008

Estuarine Coastal Science Association-Instituto Argentino de Oceanografía

Zooplankton is subjected to environmental and biological influences affecting the vertical and horizontal position of organisms in the water column. The most important factors that affect vertical distribution and abundance in estuaries are the tidal and the day/night cycles. Acartia tonsa is dominant in the Bahia Blanca Estuary and it has a broader distribution, being abundant during spring, summer and autumn. The objective of the study was to analyze the abundance of the copepod in relation to depth, tides and the day/night cycles. The sampling site was located in the major channel of the estuary (38º47’S – 62º16’W). Vertical measurements of currents, temperature, salinity and suspended sediments were carried out during two tidal cycles (25 h) in November 2007. Plankton samples were collected every three hour; with a 200 µm mesh size net. They were carried out at three levels in the water column (surface, 6 and 12 m depth), against the water flow during five minutes at a velocity of 2.5 knots. The samples were persevered in 4% formaldehyde. Fourteen zooplankton groups were found in the samples and A. tonsa represented the 97%. Significantly higher concentrations of copepodites and adults were always recorded near the bottom. No differences in the abundance were found during day and night hours and it was not observed a significant vertical migration. In relation to the phases of the tides, A. tonsa abundance was higher during low tide.