Salinity preference in gammarid amphipods with special reference toMarinogammarus marinus(Leach)

Abstract

The salinity preferences of the amphipods studied were found to correlate with distribution.Marinogammarus marinus, a marine species, showed a strong preference for higher salinity levels, the estuarineGammarus duebenishowed little avoidance of any particular sea water concentration, and the freshwaterGammarus pulexdisplayed strong preference for dilute mediaTolerance experiments showed that the preference behaviour ofM. marinuswas not caused by lethal effects of salinity.Observations onM. marinussuggested that the behaviour involved components of both preference and avoidance.InM. marinusthe choice is made on the basis of total osmolarity of the medium, not on its organic or ionic content alone.Ablation of the upper and/or lower antennae had no effect on salinity choice inM. marinus, and acclimation to 50% sea water did not alter the preference for full sea water.It is suggested that behavioural responses which confine animals to areas well within their physiological salinity limits promote survival in aquatic environments which may undergo fluctuations in salt concentration.