Larval thermal tolerances and future dispersal potential of the subtropical-to-temperate sea urchin Tripneustes australiae
The distribution and dispersal of marine ectotherms is mediated by their thermal tolerances, and as the oceans warm species distributions are shifting. Developmental thermal tolerances of marine invertebrates with a pelagic life-history phase can be used to predict the potential for local extinctions and range extensions. In southeast Australia, Tripneustes australiae is an ecologically important sea urchin species as it undergoes periodic outbreaks and can transform ecosystems through intense herbivory. We investigated the embryonic and early larval developmental tolerances of T. australiae with respect to its current distribution, to predict current and future dispersal capacity. The optimal thermal window for survival, normal development and developmental progression of T. australiae ranged between 17 and 23{degrees}C, with probability of survival at these temperatures remaining above 85% throughout the experiment. This developmental thermal window overlaps with the current thermal regime experienced across the adult distribution. This suggests that T. australiae may have a similar thermal window in its adult and early larval life history stages. Further, T. australiae may have the potential to persist at its warm-range edge into the future and to disperse and range shift poleward in coming decades. Indeed, we show that the temperature at which larvae have a 50% probability of survival may extend poleward across the Bass Strait by 2100. The persistence of T. australiae in its mid-range, its potential to disperse poleward, and increased grazing pressure from periodic outbreaks, may impact temperate macroalgal habitats already at risk from warming and concentrated grazing by other sea urchin taxa.