Latitudinal comparison of thermotolerance and HSP70 production in F2 larvae of the greenshell mussel (Perna canaliculus).

We report the first measures of thermotolerance (recorded as percentage mortality and induced HSP70 production) for pelagic larvae of three populations of the New Zealand greenshell (green-lipped) mussel Perna canaliculus. Our goal was to determine whether distinct populations of P. canaliculus were more susceptible to predicted climate change than others, and whether such patterns of susceptibility were either genetically controlled (local adaptation of populations) or simply reflect the acclimatory capacity of this species. F2 larvae from three P. canaliculus populations (D'Urville Island, Banks Peninsula and Stewart Island) were subjected to an acute thermal challenge (3 h exposure to a fixed temperature in the range 20-42°C). No latitudinal patterns in either percentage mortality or HSP70 protein production were apparent. For all populations, larval mortality (LT50) was between 32.9 and 33.9°C, with significant amounts of HSP70 induction only occurring in those individuals that experienced temperatures of 40°C or greater. The data presented therefore do not support the hypothesis that genetic adaptation of P. canaliculus to distinct thermal environments will be reflected by a corresponding difference in acute heat tolerance. In fact, the apparently vulnerable veligers show a surprisingly wide thermal safety margin. To develop a comprehensive understanding of the effects of ocean warming upon this species, subsequent studies should consider the impacts of sub-lethal stress upon fitness in addition to chronic thermal challenge and, crucially, the response of sedentary juvenile and adult stages.