Regional differences in the effects of watershed glacial coverage on the performance of Pacific Blue mussel, Mytilus trossulus

Climate change is causing atmospheric warming, leading to increasing global temperatures. Warming is especially evident in high latitude regions, leading to losses in glacial mass and consequences downstream. Pacific Blue mussels are a vital species in such downstream coastal environments where they provide services such as stabilizing substrate, facilitating energy transfer, and supporting the mariculture industry and subsistence communities. As glaciers continue to melt, it is unknown how and to what extent the projected glacial runoff will affect intertidal mussel performance. To determine the effects of glacial melt on mussel performance, mussel morphometrics (weight, length, width), mussel adhesion force, shell breaking force, and growth rates were recorded over five months at nine sites whose watersheds span a gradient of glacial coverage (0–60%) in the Gulf of Alaska (GOA). Five sites were used in Kachemak Bay (Southcentral Alaska) and four sites in Lynn Canal (Southeast Alaska). Overall, adhesion force and shell breaking force decreased with increasing glacial coverage of watersheds. However, oceanic proximity and input appear to buffer against the effects of glacial melt as mussels in the more oceanic Kachemak Bay region had higher adhesion and shell breaking forces relative to the mussels in the less oceanic Lynn Canal region. Within the more oceanic Kachemak Bay region, mussel growth rates decreased with increasing glacial coverage of watersheds. In contrast, mussel growth rates generally increased at sites with increasing glaciation of watersheds in the less oceanic Lynn Canal region. Overall, our results suggest that glacial melt is altering conditions in the nearshore marine environment and reducing mussel performance. • Gradients of watershed glacial coverage were used to estimate the impacts of glacial melt on mussel performance. • Mussel adhesion and shell breaking forces declined with increasing glacial coverage of site watersheds in both regions. • Mussel growth declined (oceanic region) and increased (inland region) with increasing glacial coverage of site watersheds. • Oceanic input may buffer against the impacts of glacial melt on mussels. • Glacial melt may increase mussel dislodgement, predation, and intertidal variability.