PLANKTON VARIABILITY IN RELATION TO SOME ENVIRONMENTAL FACTORS IN THE IMESSOUANE BAY, MOROCCO.

Our present work aims to evaluationof the richness of plankton communities and the influence of some physicochemical factors on plankton in the Imessouane Bay. The Copepods constitute more than 80% of the zooplankton communities.The phytoplankton species have maximum abundance during the summer, especially at the end of June where there are blooms of some species of harmful phytoplankton (Ceratiumfusus, Prorocentrummicans, Protoperidiniumdepressum, Dictyocha fibula).The Nitrites recorded a maximum level (July 21st) at the 10 meters depth. Low abundances of plankton populations are recorded at this depth. Above this area, high abundances of some copepod species are recorded. These results seem to be an indication that brings us to the phenomenon of surface thermocline. The canonical analysis of the correspondences allows structuring the zooplankton communities into three different groups. The first group is more abundant in the summer period ( clausocalanussp, centropagestypicus, temorastylifera).The second group present throughout the study period (paracalanusparvus, oncaeavenusta, acartiaclausi, jellyfish andsiphinophore). The third group has an affinity for nutrients (Euterpinaacutifrons and Evadne)