MEPS prepress abstract  -  DOI:

Distribution of the isopod Excirolana braziliensis on sandy beaches of the Atlantic and Pacific Oceans

Gastón Martínez, Matías Arim, Omar Defeo


ABSTRACT: We assessed geographic patterns of abundance of the isopod Excirolana braziliensis across its whole distribution range in the context of the abundant centre hypothesis (ACH). We also evaluated auxiliary hypotheses to the ACH involving habitat availability and environmental suitability. We compiled species abundance and occurrence information on 139 Pacific and Atlantic sandy beaches of the Americas. Abundance patterns were contrasted against five hypothetical distribution models. Habitat availability (sandy beach along the coast), and the role played by grain size on isopod abundance were analysed. Maximum entropy niche modelling based on primary production, salinity, water temperature and tidal range data was used to estimate trends in habitat suitability. E. braziliensis abundance peaked at the two edges of its range on the Atlantic coast and towards the centre of its range on the Pacific coast. Congruently, the niche model predicted a very low habitat suitability at the centre of the species range on the Atlantic coast. Primary production was the main contribution to the model (74.8%). The highest abundances were found in fine sediments (0.20 mm). Support for the ACH for E. braziliensis was found only for the Pacific coast, whereas habitat suitability and availability together with local in beach morphodynamics, accounted for deviations from ACH predictions in the Atlantic. The highest abundances registered in upwelling areas and in beaches with fine sands highlight the primary role played by regional and local conditions over geographic location.