The distribution of the prawn species belonging to the genus Palaemonetes is not well defined in the Mediterranean, especially in the south of France where controversy exists concerning taxonomic identification at the species level. A molecular diagnostic technique allowed us to determine without any doubt the presence of Palaemonetes varians in the Camargue. These basic results allowed us to undertake the ecological study of the species, which took place in the context of a massive 100-year flood during the winter 1993/94, leading to a rapid and major fall in salinity that remained low until 1997, before increasing. The impacts of low salinity on the catch and life history traits of Palaemonetes varians in the lagoon were investigated from 1993 to 1999. There was a positive correlation between catches and salinity. Although we observed a major decline in recruitment between the years 1993 and 1994, reproduction parameters and growth did not seem to be affected by low salinity. A comparative study of various life history traits between Mediterranean and northern environments populations was also conducted.