Reproductive potential of a marine ecosystem engineer at the edge of a newly expanded range

Abstract

Global climate change is leading to redistribution of marine species and altering ecosystem dynamics. Given recent poleward range extension of the barrens-forming sea urchin Centrostephanus rodgersii (Diadematidae) from mainland Australia to Tasmania, there is a need to understand the population dynamics of this ecologically important species in the Tasmanian environment. This paper informs possible population dynamics of C. rodgersii in Tasmania by examining its reproductive ecology in this new environment. Reproductive periodicity (gonad index and propensity to spawn) was assessed bimonthly over 18 months at four sites in eastern Tasmania spanning 2° in latitude. At all sites, C. rodgersii displayed a strong seasonal cycle in gonad production with major spawning occurring in winter (August) at minimum annual water temperature. Gametes from Tasmanian C. rodgersii were viable as determined by fertilization and early development trials. However, development to the two-arm stage at 3 weeks was strongly dependent on water temperature across the 8–20 °C temperature range, with poor development occurring below 12 °C. The range of temperatures tolerated by Tasmanian C. rodgersii larvae was similar to that of larvae from its native New South Wales range, indicating that this species has not undergone an adaptive shift to the cooler Tasmanian environment. There was also no evidence for an adaptive shift in reproductive phenology. Importantly, coastal water temperatures in eastern Tasmania during the peak spawning in August fluctuate about the 12 °C larval development threshold. Recent warming of the eastern Tasmanian coast and further warming predicted by global climate change will result in an environment increasingly favourable for the reproduction and development of C. rodgersii.