In situ spawning rate of the calanoid copepod Acartia clausi in a tropical lagoon (Ebrié, Côte d'Ivoire) : diel variations and effects of environmental factors
rate of the calanoid copepod Acartia clausi in a tropical lagoon (Ebrié, Côte d Ivoire): diel variations and effects of environmental factors. Zoological Studies 43(2): 244-254. Diel changes in the spawning rate of Acartia clausi were studied during several 24 h time series performed between 1993 and 1997 at several sites in Ebrié Lagoon (Côte d Ivoire) at which the morphology and hydrological structures differed. The daily egg production rate ranged from 8 to 60 eggs female-1 d-1 (5 % to 45 % of body carbon) and varied according to stations and periods. A correlation analysis, performed with the present results, revealed no significant effect of either envi-ronmental factors (salinity, temperature, and chlorophyll a biomass) or individual weight of females. However, the roles of salinity and food abundance (chlorophyll a) appeared when grouping the present data (1993-1997) with results from the same sites obtained previously (1981-1982) by Saint-Jean and Pagano (1984). This grouping showed the importance of inter-annual variations as compared to seasonal variations. The rhythm of egg laying was characterized by a night maximum which occurred earlier in the estuarine zone (22:00-01:00) than in the western oligohaline zone (04:00-06:00). These peaks of egg laying always occurred after the peak of gut fluorescence which was consistently observed at the beginning of the night (data from Kouassi et al
