Seasonal variation in the orientation of Talitrus saltator on a Mediterranean sandy beach: an ecological interpretation

Abstract

The amphipod Talitrus saltator (Montagu 1808), diffused on the Mediterranean and Eastern Atlantic coasts, displays physiological and behavioural adaptations to life on sandy beaches. To avoid dehydration, sandhoppers burrow in moist sand near the water’s edge during the day in the warmest seasons. When displaced, they can navigate to this safe zone using a sun compass and several additional mechanisms, both universal and local, an adaptive behaviour named ‘zonal recovery’. In this study, we analysed the effects of several variables on the talitrids’ orientation behaviour to highlight the relevance of the local cues and analyse the behavioural variation with relation to the ecology of sandy beaches. In different seasons for 2 years, orientation experiments were made on T. saltator sub-populations, at three sites of an extended sandy beach, differing in shoreline sedimentary dynamics; the main environmental, climatic and individual variables known to influence talitrid orientation were registered during each experimental session. The statistics of circular distributions were calculated and a multiple regression analysis adapted to angular data was performed, to highlight the scaling triggered by environmental conditions. The results showed that seasonal climatic variables played a primary role, adaptively modifying the sandhoppers’ behaviour. A significant interaction with the site (the chosen sites differed for sedimentary dynamics) was observed as well. A high behavioural plasticity appears to guarantee to T. saltator a good adaptation (both as abundance and geographical spreading) to life on sandy beaches, which are notably unstable environments.