The impact of estuarine salinity changes on the bivalves Scrobicularia plana and Cerastoderma edule, illustrated by behavioral and mortality responses on a laboratory assay

Salinity is a major factor impacting estuarine organisms, especially in cases of abrupt changes. The increased physiological stress frequently results in behavioral and physiological responses and in extreme cases may lead to mortality episodes. Mortality and behavioral activity of the bivalves Scrobicularia plana and Cerastoderma edule were evaluated under a wide range of salinity values. Specimens were sampled in the Mondego estuary (Portugal), acclimated and exposed to different salinity treatments (0-35) at constant temperature (20 °C). Organisms were fed daily. Mortality and individual activity were registered during 120 h laboratory assays. Both species showed an optimal salinity range for their activity (S. plana: 20-30; C. edule: 20-25), and survival was mainly affected by low salinity (S. plana: LC50120 h = 5.35; C. edule: LC50120 h = 11.09), with 100% mortality under critical values (S. plana: <5; C. edule: <10). Therefore, the occurrence of extreme climate events, especially floods, may in fact severely impact these species through drastic changes in salinity.