The thermal tolerance of the bivalves Septifer virgatus and Perna viridis, and implications for marine coastal management

Abstract

As global climate change accelerates, there is increasing concern about how ecosystems may change as a result of biodiversity loss and species replacement. Marine bivalves are important as commercial food resources, ecosystem-engineers and invasive or fouling species. Understanding how beneficial and harmful bivalve species may respond to the changing environment will be important for marine coastal management. Given the expected speed of climate change, it is unlikely that species will have time to evolve adaptively in time, instead, they will have to tolerate environmental stressors or acclimate and vary their life history traits. Studies were conducted to compare the interspecific differences in thermal tolerance between the non-invasive bivalve Septifer virgatus and the invasive Perna viridis, to see if differential tolerance can explain the invasion success of bioinvaders. The intraspecific thermal tolerance of the invasive P. viridis was also assessed to determine how thermal tolerance may differ among populations. In the second stage of the study, by acclimating both S. virgatus and P. viridis at different temperatures, the interspecific differences in thermal acclimation capacity was tested to assess their susceptibility to climate change. As the two species are ecologically and economically important, understanding how they will respond to climate change is important to help manage fisheries and coastal resources. Results showed that S. virgatus had a higher thermal tolerance than P. viridis in the cold and dry season in Hong Kong, but after acclimation at 27°C, which is the average sea surface temperature in the hot and wet season in Hong Kong, P. viridis had significantly increased its thermal tolerance and was more tolerant than S. virgatus acclimated at the same temperature, showing this species has a high capacity for acclimation. In comparison, S. virgatus showed limited acclimation capacity. The results suggest that to conclusively determine the full potential of a species' thermal tolerance, tests have to be conducted in different seasons to take into account phenotypic plasticity. The broad thermal tolerance range and the highly flexible physiology of P. viridis may represent the hallmark of a successful invasive species, and may provide a model for success in a changing world. As invasive species are generally more stress tolerant and plastic, it is expected that global climate change will facilitate bioinvasion, and efforts to manage this will need to take into account the physiological capacities of these species.