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The spatio-seasonal variations of Pseudodiaptomus hessei abundance, biomass and reproductive parameters were investigated in the Grand-Lahou lagoon at five stations during the dry and wet (or rainy) seasons from September 2005 to August 2006. In all sampling stations, abundance and biomass of P. hessei in the dry season were higher (0.16 to 2.17 ind.L-1, 0.45 to 4.97 μgC.L-1) than in the wet season (< 1 ind.L-1, 0.03 to 2.36 μgC.L-1). During the two seasons, abundances and biomass of P. hessei in the north part of the lagoon (stations 1 and 2) was higher (0.23 to 2.17 ind.L-1, 1.05 to 4.97 μgC.L-1) than in the inner part of the lagoon (stations 3 to 5: < 0.5 ind.L-1, < 1 μgC.L-1). Ovigerous females were mainly observed in the north part of the lagoon during the dry season and at stations 1 and 3 during wet season. Besides, all reproductive parameters of P. hessei present the same spatio-temporal variation. Correlation analyses showed that P. hessei abundance and biomass were negatively correlated with temperature, salinity and dissolved oxygen during the dry season. From these results, all reproductive parameters are significantly and positively correlated with nitrites and phosphates concentrations. During the wet season, P. hessei abundance were significantly and positively correlated with ammonium while biomass was significantly and positively correlated with dissolved oxygen and ammonium concentrations. During this season, no reproductive parameter of P. hessei was significantly correlated to the environmental variables. However, all reproductive characteristics were positively correlated (no significantly) with dissolved oxygen, nitrites and phosphates concentrations on the one hand, and negatively correlated with water temperature, salinity, pH and ammonia on the other hand.
Key words: Pseudodiaptomus hessei, spatio-temporal variability, biomass and production, Tropical coastal Lagoon (Côte d’Ivoire).