Succession of Phytoplankton and Zooplankton Communities Coupled to EnvironmentalFactors in the Oligo-mesotrophic Nabhana Reservoir (Semi Arid Mediterranean AreaCentral Tunisia)

摘要

The occurrence of plankton seasonal dynamicsin Mediterranean shallow lakes is characterised by a marked interannual variability, whichmakes it difficult to establish reliable predictions on the dynamics and functioning ofplankton in these ecosystems based on the Plankton Ecology Group (PEG) model. In thepresent paper we study the succession of the phytoplankton and zooplankton communities inthe semi-arid Mediterranean Nabhana reservoir (Central Tunisia) and its relationships withenvironmental factors during the period from May 2005 to January 2006 in the deepest areaof this oligo-mesotrophic reservoir. Water temperature was a keystone factors in theseasonal dynamics of zooplankton. Cyanobacteria dominated the phytoplankton communitythroughout the study year 2005-2006 (94-99%) and contributed for 93% of the total cyanobacteria abundance. The zooplanktoncommunity was dominated by copepods (66%) and cladocerans (28%). The dominant species was (66% of total zooplankton) followed by (22% of the total zooplankton). In addition,our results showed that the peak of phytoplankton abundance (5.6 ×106 cells l-1, June)coincided with that of zooplankton abundance (2.1 ×102 ind l-1, June) contrary to theclear-water phase model. The cyanobacteria and copepods were responsible for theseexceptional peaks that occurred in June, accounting respectively for 99% of the totalphytoplankton and 82% of the total zooplankton. In the Nabhana reservoir, the trophicrelationship between phytoplankton and zooplankton were implicated in the phytoplanktonabundance and dynamics. The occurrence of cyanobacterial blooms is determined by bioticand abiotic factors. The dynamics between cyanobacteria and their grazers may emerge as aregulator of blooms.