SEASONAL-VARIATIONS IN THE ZOOPLANKTON AND IN THE POPULATION-STRUCTURE OF ACARTIA-TONSA IN A VERY EUTROPHIC AREA - LA HABANA BAY (CUBA)

Seasonal changes in the abundance of total zooplankton and of main com ponents were studied at a fixed station in La Habana Bay. Special atte ntion was given to the dominant species, Acartia tonsa, which constitu ted 89% of the total number of zooplanktonic organisms. The variations in some of its population parameters (eggs, nauplii, copepodites, adu lts, sex ratio, number of eggs per female) were analysed in relation t o temperature, salinity and chlorophyll. The abundance of eggs was ind ependent of the environmental factors, particularly of chlorophyll whi ch was always present in excess. The number of eggs per female showed several peaks, but was also independent of environmental factors. Naup lii were poorly correlated with egg numbers, but depended on the abund ance of chlorophyll in particles of size <55 mu m This suggested that the part of edible food suitable for them in size or quality was not a lways in excess in the available seston, provoking a temporary increas e in naupliar mortality. The temporal evolution of the following succe ssive stages was nearly synchronous; thus, the changes observed in the ir abundance were not caused by fluctuations in the reproductive poten tial of females, but appeared to be related to a periodic decrease in the total zooplankton density due to the hushing effect of inland wate r in the bay.