Biogeographical patterns in limpet abundance and assemblage composition in New Zealand

New Zealand is an isolated landmass which straddles two major marine biogeographic provinces, across which eleven biogeographic regions have been identified. It also supports a high biodiversity of endemic rocky intertidal species. Although the distributions of many of these species were qualitatively described several decades ago, little quantitative data on abundance, distribution and diversity has been collected across a range of spatial scales from local to biogeographical. Without such data it is difficult to assess range dynamics and connectivity of endemic and climate-sensitive species and assemblages, and thus predict responses to future impacts of climate warming, sea level rise, coastal squeeze and ocean acidification. This paper documents the geographic distributions, abundances and assemblage patterns of intertidal limpets at 63 sites around the New Zealand coast. Limpets are key functional components of most temperate ecosystems, influencing patterns of invertebrate–macroalgal dominance, carbon cycling and biodiversity. In contrast to continental-scale studies in other temperate systems, limpet assemblages were not more similar at the level of the biogeographic province, and only weak associations were found with biogeographic region. Limpet assemblages did differ between sites, but no spatial pattern was evident. Species distributions and assemblage structures did also not appear to be strongly influenced by environmental factors including temperature, coverage of key structural taxa including barnacles, mussels and macroalgae, or other potentially competing grazers. Limpet diversity was highest at some exposed locations, but there was no national trend. In general, the high variability we observed in individual species abundances at local, regional and biogeographic scales suggests that small scale, local factors rather than broad biogeographic drivers determine New Zealand rocky intertidal limpet assemblages. This creates a challenge for ecological forecasting of future responses to global environmental change.