BURROW-ZONE DISTRIBUTION OF THE SUPRALITTORAL AMPHIPOD TALITRUS SALTATOR ON DERBYHAVEN BEACH, ISLE OF MAN―A POSSIBLE MECHANISM FOR REGULATING DESICCATION STRESS?

Abstract

ABSTRACT Following nocturnal intertidal foraging migrations, the supralittoral sand-beach talitrid amphipod Talitrus saltator establishes a discrete burrow zone at the top of the shore in which individuals remain quiescent during the daytime. The position of the burrow zone and the depth to which individuals burrow varies both on a seasonal and spring-neap tidal basis. During winter, T. saltator typically burrows higher upshore, usually beyond the influence of tidal inundation above EHWS, and to a greater depth. Following a spring migration downshore, the population maintains a burrow zone between mean high water spring and mean high water neap during the summer breeding period of May-August. During this time, individuals tend to burrow to a shallower depth and the burrow zone alters on a semilunar basis to avoid spring tide inundation. Individuals also display burrow-position and burrow-depth variations in respect to reproductive condition, with egg-bearing females found higher upshore, and also in respect to age, since developing juveniles are typically found lower on the shore and burrow to shallower depths than adults. The variations in burrow-zone location and burrow depth adopted are interpreted as behavioral mechanisms associated with the amphipod's efforts to reduce diurnal desiccation stress.