Ecological strategies of Macarorchestia remyi compared to two sympatric talitrids of a Tyrrhenian beach

In sandy beach ecosystems habitat partitioning represents an effective way of avoiding competition among sympatric species. This together with specific behavioural adaptations allows species to coexist in spatially restricted areas. This study analyses the behavioural and trophic ecology of Macarorchestia remyi a driftwood species which lives together with Talitrus saltator and Orchestia gammarellus along a beach-dune ecosystem of the Maremma Regional Park (Grosseto, Italy). Relative abundance and distribution patterns of M. remyi were obtained through an active search of the species and with pitfall traps. The diets of the three sympatric species were assessed with the use of stable isotope analysis and the contribution of each food item was determined. Sun orientation experiments were performed in the field and scototaxis responses to a black silhouette were tested at noon and at midnight. The study aimed to determine if there was a trophic segregation and evidence of differences in the behavioural responses of the three sympatric species. M. remyi rarely moved from its shelter and showed morphological and behavioural characteristics very different from the other two sympatric species. The maintenance of the driftwood habitat was achieved thanks to a simple scototactic response both during the day and night. M. remyi was the most generalist species exploiting any food item that could reach its refuge and thus had a relatively high dietary overlap with the other two scavenger species. The behavioural responses of the three species were compared and discussed in terms of their ecological adaptations to the different occupied niche.