Ecophysiology and stress response of marine and brackish water Gammarus species (Crustacea, Amphipoda) to changes in salinity and exposure to cadmium and diesel-oil

There is a current debate whether organisms living in estuaries should be more sensitive to pollution than their marine relatives, but few comparative studies have been made. Amphlpods of the genus Garnrnarus are generally euryhaline and 5 species are common to the braclash Baltic Sea (7 %O S) and the North Sea (30 %O S). Laboratory measurements on the metabolism of G. duebeni and G. oceanicus from the 2 areas showed that respiration and 0xygen:nitrogen ratios of G. duebeni were generally less affected by salinity changes and/or additions of diesel oil and cadmium than G. oceanicus. We interpret this as a higher tolerance of G. duebeni to pollutants and salinity changes. probably coupled to this species being physiologically broad-niched and having evolved in, and being adapted to, physically more variable environments. The Baltic populations of G. duebeni and G. oceanicus were generally more sensitive to salinity changes and treatments with diesel-011 than their North Sea conspecifics. The higher sensitivity to pollutants of the Baltic populations may be due to a number of factors such as changes in the characteristics of toxic substances (metals) with salinity, the higher relative ionic concentration of a given amount of poisonous substance in the low-saline Baltic Sea than in the North Sea, and direct interactions of toxicants with membrane permeability and osmoregulatory mechanisms, which are already under strain at low salinities.