The role of salinity in the selection of biological traits of freshwater invertebrates

Abstract: Salinity exerts significant pressure on freshwater faunas living in slightlysalted water (i.e. water with salinity < 3gL –1 ). Changes in seven biological and phy-siological characteristics of freshwater taxa belonging to natural invertebrate commu-nities observed along a salinity gradient were investigated. Benthic macroinvertebrateswere sampled from four stations on the Meurthe River, a six-order stream in northeast-ern France with a gradient ranging in concentrations from 0.21g L –1 to 2.60g L oftotal dissolved solids over a distance of only 19km. A fuzzy coding of seven traitsallowed us to quantify the potential physiological requirements or biological traits ofeach species or genus observed. The consideration of whole assemblages highlightedtrends in the use of each modality by communities along the salinity gradient. Achange in many invertebrate traits was observed. Ovoviviparity was important at thestation with the highest salinity, the internal development of eggs in females mostprobably contributing to a better protection of the young. In contrast, this reproductivetype, leading to physiological constraints and limited fecundity, was less adopted inless salted sites.A modification in benthic community feeding habits along the salinitygradient was also discovered.An increase in deposit feeders at the expense of scrapersand piercers was observed. This pattern is in accordance with an energy transfer in theecosystem from water column (i.e. suspended organic material) to river bed (depositedorganic material) along the salinity gradient.Key words: benthic macroinvertebrates, freshwater, biological traits, salinization.