Qualitative and quantitative study of phyto- and zooplankton communities in the saline pounds of Sfax, Tunisia
Paralic ecosystems are transitional systems between marine and continental areas. Thalassohaline waters where brines are formed by evaporation of seawater in land-locked bays or lagoons, such as salt pans or salt works, are representative of these systems. Except for the studies on the ecology and biogeography of the brine shrimp Artemia, few attemps have been made to analyze phyto- and zooplankton communities in salt works, especially those located in zones subject to arid conditions. Herein, we examined the seasonal dynamics of phyto- and zooplankton assemblages in a salt works located in the central area of the eastern coast of Tunisia (Sfax, ~36°N, 11°E), from August 1999 to May 2000, concurrently with a variety of environmental parameters. Phyto- and zooplankton communities were substantially diversified and their dynamics were apparently in relation with the salinity in the pans and the resource availability. During the study, phytoplankton populations were quantitatively and successively dominated along the salt works by diatoms in primary pans (salinity < 200‰), followed by dinoflagellates in intermediate pans (salinity=200-300‰), and by a near monospecific development of the chlorophycean Dunaliella salina in salt production pans. Zooplankton (> 20 μm) organisms were quantitatively dominated by rotifers and/or copepods in primary pans in Summer and Autumn, by ciliated protozoa during Winter in intermediate pans, and by a near monospecific development of the brine shrimp Artemia in the salt production units of the salt works. Artemia exhibited their highest abundances in Spring. Overall, we conclude that the diversity, the development and the dynamics of biological populations in the Sfax salt works are a consequence of the salinity of the milieu, likely coupled with the resource availability.