Physiology and biogeography: The response of European mussels (Mytilus spp.) to climate change

To understand how ecological communities may respond to climate change we have adopted the approach of determining the response of major ecosystem engineers that determine community composition and function. We utilize two approaches, correlative and mechanistic, to understand the current and future distributions of the marine mussels Mytilus edulis Linnaeus, 1758 and M. galloprovincialis Lamarck, 1819 in Europe. Both are dominant space-occupying species that control biodiversity in many coastal ecosystems and are the basis of the largest aquaculture production in Europe. A mechanistic analysis of physiological energetic response to temperature of the two species indicates that Mytilus edulis cannot sustain a positive energy balance for sustained periods when sea surface temperature (SST) is greater than 23 degrees C, while M. galloprovincialis can maintain a positive energy balance at SST up to 30 degrees C. There is no difference in energetic response of the two species at cold temperatures (5-10 degrees C). The upper temperature threshold of positive energy balance in each species corresponds closely to the distribution of SST at their respective southern range limits in Europe. Alternatively, the northern range limit of M. galloprovincialis coincides with areas where winter SST is less than 9 degrees C, but there is no evidence of an energetic limit to this species at the cold end of its geographic range. Presently there is no mechanistic explanation for the difference between species in their northern range limits; however, as indicated by Random Forest modeling, M. galloprovincialis appears to be limited by cold temperatures during winter, suggesting the hypothesis of failure in reproductive development. These approaches allow for the ability to forecast changes in the distributions of these two species in Europe as SST continues to increase.