Variation of apparent permeability to water and sodium transport in Gammarus duebeni exposed to fluctuating salinities

Abstract

1. 1. The blood sodium concentrations, body water content, drinking rate, active uptake of sodium and apparent permeability to water of the amphipod Gammarus duebeni in non-steady state systems are described. 2. 2. The apparent permeability to water of Chaetogammarus marinus has been investigated. 3. 3.Exposure to a salinity cycling between 3 and 97% seawater with a period of 12 hr 25 min results in dramatic changes in the apparent permeability to THO in G. duebeni, but only a small change in the case of C. marinus. 4. 4. The blood sodium concentration of G. duebeni varies by only some 60 mM l −1 during the cycle and in consequence is hypotonic to the medium for those periods when the external concentration exceeds about 350 mM l −1 Na. 5. 5. The active influx of sodium by G. duebeni is least when the external salinity is highest and has reached its nadir before blood sodium concentration starts to fall. 6. 6. Total body water and drinking rates show no consistent trends in the cycle. 7. 7. The adaptive features of the response of G. duebeni are discussed.