Is the copepod egg production in a highly turbid estuary (the Gironde, France) a function of the biochemical composition of seston?

The influence of the biochemical composition of particles originating from surface waters of the Gironde estuary on egg production rates of Eurytemora affinis zooplanktonic population was studied. In the high turbidity zone, suspended particulate matter had a low nutritional quality because the easily available organic fraction represented less than 15% of the overall particulate organic matter. In waters located seaward of the high turbidity zone, a slight increase in nutritional quality was observed. As a result, the sum of easily extractable organic macromolecules represented 15 to 33% of the overall particulate organic matter. The present study suggests that the low egg-production rate of Eurytemora affinis, occurring in the high turbidity zone, results from combined effects of temperature and bad feeding conditions in the area. Low copepod production can be explained by little phytoplankton growth due to light limitation and, therefore, restricted food availability, as well as difficulties in food selection, non-living particle may being dominant.