Zooplankton distribution in four ponds of different salinity: a seasonal study in the solar salterns of Sfax (Tunisia)

The seasonal distribution of metazooplankton and large-sized ciliates was studied in four ponds of different salinity in the solar salterns of Sfax (Tunisia). Total zooplankton abundance varied from 1 × 10³ to 4.7 × 10⁶ ind m^–3. Salinity had a negative effect on the abundance of copepods and rotifers which were absent in the pond with the highest salt concentration (180) in which the number of taxa was low and Artemia or the ciliate Fabrea largely dominated the zooplankton community. Temperature and the presence of Dunaliella salina as prey appeared as key factors in controlling the abundance of Artemia, while organic detritus appeared as important in the diet of Fabrea. Change in zooplankton species composition along the hypersaline gradient (40–90) was primarily related to salinity. However, our data suggest the importance of both the abundance and composition of food in the spatial and temporal variations of some zooplankton species.