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Projecting ecological and evolutionary responses to variable and changing environments is central to anticipating and managing impacts to biodiversity and ecosystems. Current model- ing approaches are largely phenomenological and often fail to accurately project responses due to numerous biological processes at multiple levels of biological organization responding to environmental variation at varied spatial and temporal scales. Limited mechanistic under- standing of organismal responses to environmental variability and extremes also restricts predictive capacity. We outline a strategy for identifying and modeling the key organismal mechanisms across levels of biological organization that mediate ecological and evolutionary responses to environmental variation. A central component of this strategy is quantifying timescales and magnitudes of climatic variability and how organisms experience them. We highlight recent empirical research that builds this information and suggest how to design future experiments that can produce more generalizable principles. We discuss how to create biologically informed projections in a feasible way by combining statistical and mechanistic approaches. Predictions will inform both fundamental and practical questions at the interface of ecology, evolution, and Earth science such as how organisms experience, adapt to, and respond to environmental variation at multiple hierarchical spatial and temporal scales. 

Anthropogenic warming and natural climate variability affect global patterns of seawater temperature and marine primary productivity and affect organism survival, growth, and physiology. Mussels are ecosystem engineers that utilize byssal thread structures to attach to hard substrate, a strategy key to survival in wave-swept rocky shore environments. Byssal thread production varies according to season and environmental conditions, and temperature and food availability may influence the production of these structures by affecting energy limitation. Mytilus trossulus and M. galloprovincialis are congeneric mussel species in the Northeast Pacific with cold- and warm-adapted thermal tolerances, respectively. First, we hypothesized that temperature has opposing effects on growth rates of the 2 species. Second, we hypothesized that either (1) byssal thread production is positively correlated with growth rate (the ‘production’ hypothesis), or (2) there is a trade-off between growth and byssal thread production, and resources are allocated first to byssal thread production rather than growth. Under this ‘trade-off’ hypothesis, we predicted no relationship between growth rate and byssal thread production. We manipulated seawater temperature and food availability and quantified mussel performance in terms of survival, growth, and byssus attachment. Across all treatment combinations, we found that M. galloprovincialis had positive shell and tissue growth and M. trossulus had minimal shell growth and a loss in tissue mass. Temperature had opposing effects on each species; temperature increased shell growth of M. galloprovincialis but increased tissue loss of M. trossulus . Temperature did not affect byssal thread production, and there was no significant relationship between byssal thread quality or quantity and shell or tissue growth across the temperature and food gradient for either species. Our results suggest that energy allocation is prioritized towards byssal thread production over growth. 

Ocean warming and acidification are predicted to impact the physiology of marine organisms, especially marine calcifiers that must deposit calcium carbonate and resist dissolution. Of particular concern are articulated coralline algae, which must maintain both calcified segments (intergenicula) and uncalcified joints (genicula) in order to thrive along wave-swept rocky coastlines. We examined the effect of pH and temperature, both individually and in combination, on the growth, calcification, and biomechanical properties of 2 species of articulated coralline algae, Corallina vancouveriensis and Calliarthron tuberculosum , common on wave-exposed shores in the NE Pacific. Increased temperature and reduced pH were found to reduce growth rates in both species (30-89% lower) but had little influence on the amount of intergenicular calcium carbonate or on the genicular biomechanical properties of these species. Results suggest that although growth rates may decline, these 2 coralline species will maintain the integrity of their tissues and continue to persist under future climate stress. 

Organisms rely on the integrity of the structural materials they produce to maintain a broad range of processes, such as acquiring food, resisting predators, or withstanding extreme environmental forces. The production and maintenance of these biomaterials, which are often modulated by environmental conditions, can therefore have important consequences for fitness in changing climates. One well-known example of such a biomaterial is mussel byssus, an array of collagen-like fibers (byssal threads) that tethers a bivalve mollusk securely to benthic marine substrates. Byssus strength directly influences mortality from dislodgement, predation, or competition and depends on the quantity and quality of byssal threads produced. We compared the temperature sensitivity of byssal attachment strength of two mussel species common to the west coast of North America, Mytilus trossulus and M. galloprovincialis, when exposed to seawater temperatures ranging from 10 to 24°C in the laboratory. We found that the two species attached equally strong in seawater ≤18°C, but higher temperatures caused byssal thread production rate and quality (break force and extensibility) to be greatly reduced in M. trossulus and increased in M. galloprovincialis, leading to a 2–10-fold difference in overall byssus strength between the two species. Using this threshold value (18°C), we mapped habitat for each species along the west coast of North America based on annual patterns in sea surface temperature. Estimated ranges are consistent with the current distribution of the two species and suggest a potential mechanism by which ocean warming could facilitate the northern expansion of M. galloprovincialis and displacement of native M. trossulus populations.