Seasonal temperature stress, biotic interactions and their effects on blue mussel physiology in the Gulf of Maine

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Predicting how species will respond to climate change is one of the biggest challenges facing ecologists today. The complex interaction between environmental variability and physiological tolerance at multiple scales is still not well understood, making it difficult to predict how future change will impact ecological communities. Although climate change is expected to result in an overall warming trend, climate-driven weather effects are predicted to vary by region. Extreme weather events-such as heat waves, dry spells, cold snaps and increased precipitation-are forecast to increase in frequency. Although important, the interactions between seasonal stressors are often overlooked when trying to forecast the effects of climate change. Winter stress, in particular, has often been overlooked in studies on intertidal organisms, and can interact with conditions in the spring and summer to influence patterns of growth and fecundity in temperate species. In this dissertation I present a framework examine how the effects of daily cycles, seasonal changes, extreme events, and species interactions impact organismal physiology and population-level persistence, across regions of the same coastline. In the first chapter, I investigated regional and seasonal differences in substrate-mediated temperature effects on the blue mussel, Mytilus edulis, and how these thermal regimes drive exposure, susceptibility, and vulnerability in populations throughout the Gulf of Maine. In the second chapter, I utilized the broad thermal tolerance of M. edulis to understand the sublethal effects of daily freeze-thaw cycles and the impact of aseasonal warm spells on respiration, feeding, and growth. For the third chapter, I investigated the interactive effects of biotic and abiotic stress by comparing the cardiac response in starved and fed M. edulis to biochemical indicators of metabolism and oxidative stress when exposed to acute heat stress and predation risk over short time scales. The fourth chapter is a review of existing methodologies and trade-offs in ecological forecasting and considerations for selecting a forecasting approach. Overall, this dissertation identifies differing sensitivities to thermal stress across populations of M. edulis in the Gulf of Maine, including sublethal physiological impacts from winter intertidal exposure, and summer thermal stress under threat of predation risk and starvation. An analysis of thermal patterns in soft-sediment mussel beds along a northeast-to-southwest "gradient" revealed a mosaic of thermal stress both within- and across-sites, that is highly dependent on seasonality and inter-annual variation in weather patterns. These results further emphasize a need to understand how spatial and temporal variability in both biotic and abiotic stress scales from individuals to populations to impact large-scale patterns of distribution and community structure.--Author's abstract