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Dynamics of the copepod Eurytemora affinis hirundoides in the Gironde estuary: Origin and fate of its production
Jacques Castel, A. Feurtet

In the Gironde estuary, Eurytemora affinis hirundoides is by far the most abundant planktonic species. Its production was estimated during a one year study from samples taken at 10 days intervals. Production was calculated by dividing population biomass by turnover times based on laboratory data. We found an annual production of 1.4 g C m-3 By comparison, the mean primary production in the channels of the Gironde estuary was no more than 6.3 g C m-3 yr-1. Assuming a growth efficiency of 9-18 %, 7.8 to 15.6 gC m-3 yr-l are consumed by the copepods. This means that the primary production could only sustain 40-80 % of the copepod populations, and that detritic pathways must play a prominent role. The distribution pattern of E. a. hirundoides showed a clear relation with the suspended particulate matter. Several evidences suggest that the copepods feed on detritus. However, an excess of suspended matter (> 1 g l-1) may restrict the downward distribution of E. a. hirundoides as the consequence of a physical conglomeration in the turbidity maximum zone. The copepod populations are retained within the estuary in the same way as the sediment and could be trapped for more than one generation. Since the turbidity maximum is expelled during short periods of time (35 days per year in all), most of the copepod production may remain within the estuary where it is recycled, partly by predation. It is concluded that this amount of organic matter does not serve to fertilize the continental shelf, at least in the form of particulate matter.

Keywords: Eurytemora, Copepoda, biomass, production, estuaries.
Contents of this volume Sci. Mar. 53(2-3) : 577-584 Back PDF
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