Environmental factors impacting the abundance and distribution of amphipods in intertidal rock pools

Intertidal rock pools are considered critical habitats along coastal shores. Amphipods play an important role in intertidal rock pool ecosystems, as food resources for higher trophic levels and sometimes by enriching nutrients through grazing. However, the environmental factors driving their rockpool occupation remain largely unknown. We aimed to examine the importance of the large-scale wave action variation and meso-scale shore variation on the abundance and diversity of rockpool amphipods. A total of 32 intertidal rock pools on four Portuguese shores were studied during the summer spring tide of 2015. We applied multivariate analysis to evaluate the potential impact of wave action (sheltered versus wave exposed shores), physical pool structure (length, width, and depth), and relationships within the pool community on the abundance and diversity of amphipods. Wave exposure significantly influenced amphipod abundance and diversity, and some substrata and biodiversity features of the pool were important in explaining the amphipod abundance. The percentage and composition of coverage and physical features of the rock pools had no significant effect on amphipod abundance and diversity. We showed that the amphipod rockpool community displayed a clear positive response of biodiversity and abundance to the extrinsic factor wave action, and a varied and complex response to within-rockpool biotic variables. In addition, we recorded the presence of the invasive Ampithoe valida for the first time on rocky shores of Portugal. Further investigation into the influence that wave action has on associated pool biota (i.e., dislodgment or deposition of species) could give additional insight into the role of the biotic community in the regulation of amphipod populations within intertidal rock pools