Egg production and hatching success of Eurytemora americana, an invader copepod in the Bah¨ªa Blanca Estuary, Argentina

BERASATEGUI, A. A.; HOFFMEYER, M. S.; BIANCALANA, F.; FERNÁNDEZ SEVERINI M. D.

Bah¨ªa Blanca

Congreso; ECSA44; 2007

IADO

EGG PRODUCTION AND HATCHING SUCCESS OF EURYTEMORA AMERICANA, AN INVADER COPEPOD IN THE BAHIA BLANCA ESTUARY ARGENTINA A. A. Berasategui *, M. S. Hoffmeyer,  F. Biancalana, M. Fernadez Severini. Instituto Argentino de Oceanograf¨ªa, Consejo Nacional de Investigaciones Cient¨ªficas y T¨¦cnicas. Camino La Carrindanga Km 7,5. B8000FWB Bah¨ªa Blanca, Argentina. *E-mail: aberasa@criba.edu.ar E. americana is an estuarine copepod native of northern hemisphere. It was accidentally introduced through ballast water in the Bah¨ªa Blanca Estuary in the mid-eighties. This copepod develops a planktonic pulse in winter and spring. Its population has increased in density over the last years associated with environmental changes. There are no previous reports, according to our knowledge, on experimental studies about the reproductive strategy of this species. In the present study, egg production and hatching success of this species were examined in relation to environmental variables (temperature, salinity and chlorophyll-a). Experimental incubations were conducted in the laboratory, simulating the natural conditions of temperature and salinity during the 2007 annual pulse. At each incubation experiment, egg-carrying females selected from the mesozooplankton samples, were placed in 100 ml dishes and fed  with natural food (seston < 60 ¦Ìm). The obtained results suggest that the higher egg production (40-66 eggs) would be associated with high salinity (30-33.9), low temperature (5-7¡ãC) and mainly with high availability of food (chlorophyll-a concentration of 15-20 mg /m3). These conditions seem to induce females to produce subitaneus eggs (those hatching immediately). This was demonstrated by the high hatching success (96-100%). On the other hand, a reduction in hatching success was observed when salinities fall below 30 and temperatures raised above 12¡ãC. These conditions associated with the phytoplankton peak declination could be the factors that induce the resting egg-laying. The diapausal character of these eggs was corroborated by their hatching after two or three months from incubation.