Osmoregulation and sodium balance inCrangon vulgaris(Fabricius) (Crustacea, Natantia) in varying salinities

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Abstract
Specimens of the decapod crustacean Crangon vulgaris from the Øresund were found to be hyperosmotic in salinities below 25‰ and hypo-osmotic above this salinity. The hyperosmoticity is larger and the hypo-osmoticity smaller than earlier reported for Crangon from the North Sea. This feature is considered an adaptation to the lower salinity prevailing in Baltic waters. Sodium is maintained more concentrated to the medium up to 400 mEq/1 and less concentrated in media above this value. The ability to keep its haemolymph concentration so independent of the outer medium is made easier by a low surface permeability. Crangon adapts its haemolymph sodium to a changed outer medium already after 3–5 hours. When the animals were transferred to a higher salinity the sodium concentration in the haemolymph initially rises and decreases again after ca. 2 hours; when transferred to a lower salinity the sodium concentration decreases steadily till a new steady state is achieved.