The effect of salinity changes on the population structure and reproductive traits of Crangon crangon L. populations in the Camargue (Rhone Delta, France)

Environmental factors, especially salinity, play a major role in the life c ycle and ecology of aquatic organisms. Hundred year return-time floods in t he river Rhone (southern France) in the winter of 1993-1994 led to a rapid and major fall in salinity (from 15 g/L to 5 g/L) within the Vaccarez lagoo n system. Salinity remained low until 1997, and then started to increase. T he impact of low salinity on the catches and reproductive traits of Crangon crangon L. in the lagoon were investigated from 1993 to 1999. The species is annual in the system, a single cohort being present each year in the lag oons. No correlation was found between catches and salinity within lagoons. Although a causal relationship could not be demonstrated during this field study, reproductive success seemed to be affected by low salinity. The per cent of ovigerous female C. crangon in lagoons was lowest both in the years and in the sites where lowest salinity was recorded. Moreover, in those lo w salinity sites, the relative fecundity of females was significantly lower . Several hypotheses explaining these results are discussed. The most likel y c explanation is that osmotic stress led to high energy costs fdr brown s hrimps entering lagoons with low salinity, which resulted in a trade-off be tween energy invested in maintenance and reproduction.