Presence and seasonal variation of heterotrophic dinoflagellate Gyrodinium fusus (Meunier) akselman in the estuary of Bahia Blanca, Argentina

Abstract

Gyrodinium fusus (Meunier) Akselman, which has been reported for the Argentine shelf at 36º and 37º 40´S and the Río de La Plata Estuary is observed for the first time in the Bahía Blanca Estuary. Heterothophic dinoflagellates, due to a wide range of feeding strategies, become important to the trophic dynamics of plankton community. We analyze the seasonal variations of G. fusus in the estuary in relation to the bio-physicochemical variables during an annual cycle. Sampling was carried out from March 2003 to March 2004. Water temperature, salinity, Secchi distance, solar radiation, chlorophyll “a”, phaeopigments and nutrients were measured. Enumeration was made under inverted microscope. The presence of G. fusus was restricted to winter-early spring. Maximum abundance (6,200 ind. l-1) was registered during winter. A positive highly significant correlation (Pearson, p< 0,01) was found between the abundance and Secchi distance. Possible causes of G. fusus intrusion into the estuary are inferred. The occurrence of G. fusus in the estuary enlarges its geographical distribution for the argentine Coast.