LAUSR

Microphytoplankton and environmental parameters were monitored and analyzed bimonthly (twice a month) over an annual cycle (June 2011 to May 2012) at six stations in Oualidia lagoon. The present study is conducted to assess the relationship between physicochemical parameters and microphytoplankton assemblages, which can serve as a method to assess the quality of paralic ecosystem. The assessment results revealed a seasonal variation of nutrients concentrations. Spatial variation of temperature, salinity and concentration of dissolved oxygen was noticed. Two microphytoplankton classes were dominant: Bacillariophyceae and Dinophyceae. The phytoplankton diversity and abundance were characterized by a pronounced seasonal pattern. Canonical correspondence analysis between environmental variables and dominant taxa of phytoplankton indicated the tidal influence on microphytoplankton distribution in Oualidia lagoon. Concentrations of nitrite, salinity, pH and temperature showed a positive correlation with dinoflagellates and diatoms indicating their importance in microphytoplankton growth and sustenance. Concentrations of orthophosphates developed negative correlation with microphytoplankton. Finally, fifteen taxa were identified that may present a risk of inducing harmful blooms (Pseudo-nitzschiasp., Dinophysisacuminata, D. acuta, D. caudata, D. fortii. D. sacculus, Phalacromarotundatum, Gonyaulaxpolygramma, Lingulodiniumpolyedra, Ostreopsissp., Pelagodiniumsp., Gyrodiniumspirale, Heterocapsasp., Prorocentrumcordatum and P. micans).