Biogeography of intertidal invertebrates is influenced by latitude along the west coast of Australia

Along the west coast of Australia, intertidal rock platforms support high invertebrate diversities that provide vital ecosystem services, yet patterns in diversity are not well understood. Here, we document and examine the invertebrate assemblages on intertidal rock platforms in Western Australia and delineate ecoregions according to assemblage structure. We recorded 406 invertebrate species from quadrat and timed search surveys on 39 intertidal limestone platforms that span 16° of latitude. We analysed latitudinal variation in species assemblage composition and multiple components of invertebrate diversity (alpha, gamma and beta diversity) that relate to different spatial scales (local, regional and bioregional) using multivariate analysis of variance and distance‐based linear models. Bioregions of similar invertebrate assemblages were delineated using hierarchical cluster analysis with unweighted pair‐group methods using arithmetic averaging. There was a clear relationship between alpha and gamma diversity, with both increasing towards the equator. Beta diversity was relatively high across all sites, not showing any significant variation with latitude, highlighting how regional patterns can arise from sites with high local variation. Our results indicate that the intertidal diversity aligns with the latitudinal diversity gradient theory, demonstrating how regional‐scale processes influence patterns in diversity. The composition of species distributions across latitudes indicates that a transition between tropical‐ and temperate‐dominated assemblages occurs between 27–24°S, although further research is required to examine the properties of the transition zone. Distinct groupings of invertebrate assemblages were identified, which delineated the coast into five regions. We provide a comprehensive empirical understanding of invertebrate assemblages along the west coast of Australia, which acts as a valuable baseline to assess future change and aid future management and conservation efforts.