Behavioural adaptations of two sympatric sandhoppers living on a mesotidal European Atlantic sandy beach

Behavioural adaptations of supralittoral species on sandy beaches are expressed as responses a response to environmental changes and constitute a key factor in their survival and evolution. Two sympatric talitrid amphipods (Talitrus saltator and Britorchestia brito) from a mesotidal exposed sandy beach on the European Atlantic coast (Portugal) were compared as regards behavioural adaptations of orientation and littoral zonation patterns in under natural conditions. Orientation experiments were carried out during the hottest seasons (spring and summer 2011 and 2012) at Quiaios beach, a highly dynamic exposed sandy beach. Multiple regression models were fitted to the angular data and the environmental effects on orientation were investigated for each species. Both talitrids resulted well orientated towards the shoreline and finely tuned to the mesotidal environment but a different use of local cues and climatic features in between both the two species was apparent. T. saltator showed a less lower precision in the orientation performance (with a bimodal distribution sea- and land- wards), with less dependence on the sun cues and higher dependence on climatic conditionsfeatures. In addition, the zonation of T. saltator was across the land-sea axis during both sampling seasons. For B. brito the landscape vision, sun visibility and the tidal range time enhanced the orientation to the shoreline. On this mesotidal Atlantic beach, T. saltator appeared to have a more flexible orientation with respect to B. brito, which appeared to be more dependent to on the conditions offered by the intertidal zone, a behaviour confirmed by its restricted zonation below the high tide mark. Consequently, T. saltator showed a more flexible behaviour that may be considered an important evolutionary adaptation to dynamic and mesotidal sandy beaches. Keywords: sandy beaches, mesotidal, Orientation behaviour, talitrid amphipods, Talitrus saltator, Britorchestia brito.