Humidity Reactions of Three Aquatic Amphipods, Gammarus Duebeni, G. Oceanicus and Pontoporeia Affinis in the Air

Abstract

1. Specimens of the Baltic population of the aquatic amphipods Gammarus duebeni and G. oceanicus are able to avoid the lower of two relative humidities of the air when out of water. 2. This humidity reaction is based on the orthokinetic and the klinokinetic types of orientation. 3. G. duebeni is an inhabitant of seashore rock pools and has been reported to move on land between the pools. 4. Although G. oceanicus is seldom exposed to air in nature in the practically tideless Baltic area, it lives between tide-marks in other parts of its distributional range. 5. The third amphipod studied, Pontoporeia affinis, does not discriminate between high and low humidities of the air in an alternative chamber. It is always confined in nature to the sea bottom below the low tide level. 6. Of the three studied species, individuals of G. duebeni move rapidly on dry land and survive a markedly longer time in humid air than the amphipods belonging to the two other species.