Environmental control of community organisation on ocean-exposed sandy beaches

Models of faunal communities on open-coast beaches emphasise the primacy of environmental conditions in determining species richness and abundance. What remains unresolved under this 'physical-control paradigm' includes the following two aspects: (1) how habitat properties relate to structural traits of communities; and (2) how environmental conditions shape communities when habitat properties change over time. Here, we test these by modelling the relationship between a broad range of environmental drivers and assemblage structure. Our models draw on a sizeable dataset (15 600 cores collected over 4 years) of benthic invertebrates from beaches in eastern Australia; we also include a test of whether human disturbance (vehicles) alters the relationships between environmental predictors and faunal communities. A suite of physical factors, comprising habitat features (i.e. moisture level, grain size, beach slope) and wave parameters, explained variation in community structure. Novel aspects are the role of sea-surface temperature (SST) as a driver of biological structure on beaches, and that human impacts can override the sediment-animal relationships that are normally important. More generally, theoretical and empirical models of beach-community organisation should incorporate multiple environmental drivers, include broader structural aspect of assemblages, and recognise the role of human habitat alterations in shaping these fauna-environment links.