How does embryonic and larval thermal tolerance contribute to the distribution of the sea urchin Centrostephanus rodgersii (Diadematidae) in New Zealand?

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Sea surface temperature (SST) influences the physiology of marine invertebrates, and, in turn, their geographical distribution. The Diadematidae sea urchin Centrostephanus rodgersii has expanded its range in Eastern Australia as a result of increased winter sea temperatures, and there is interest in the potential for the species to increase its range and abundance in New Zealand. We investigated the extent to which embryonic and larval thermal tolerance of fertilization, cleavage, hatching, gastrulation and appearance of plutei may control the distribution of the adult populations in New Zealand. We also compared these individuals with an Australian population in northern New South Wales at Coffs Harbour from a region just north of where the Eastern Australian Current gives rise to the Tasman Front current to New Zealand. The aim of the present study was to find evidence for adaptation in fertilization and the developmental stages to New Zealand winter sea temperatures. Fertilization was not affected by temperature over a broad thermal range (12.0°C–26.4°C and 12.8°C–29.5°C for the New Zealand and the Coffs Harbour population respectively). The first cleavage, hatching, gastrulation and appearance of plutei were more sensitive to temperature and occurred within a well-defined thermal window (17.2°C–23.5°C in New Zealand and 17.3°C–24.5°C in Coffs Harbour). The sites where C. rodgersii adults have been reported in New Zealand lie on the 15°C winter isotherm, consistent with our findings with regard to the lower temperature for pluteal development for the New Zealand population. We found evidence for a shift in thermal tolerance between the two populations of C. rodgersii examined, with fertilization and each developmental stage showing an upper thermal limit consistently shifted by ≈1°C towards lower temperatures in New Zealand individuals. Our findings indicate that the thermal window for larval development of C. rodgersii may contribute to its present distribution in New Zealand. In addition, given that larval development in New Zealand presently occurs at the colder limit of the thermal window of C. rodgersii, there may be the potential for a future expansion of its distributional range under future ocean warming scenarios.