Integrating the effects of complex environmental variation across levels of biological organization in marine ecosystems

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Anthropogenic greenhouse gas emissions are already having measurable effects on the Earth's biota. However, because patterns of environmental change and the biological systems responding to that change are both complex, the ecological responses to climate change are often quite difficult to predict. In marine ecosystems, two of the primary drivers of change are global warming and ocean acidification (OA). Typically, the effects of these two drivers are studied in isolation, and their effects are often investigated one species at a time. These approaches, while relatively straight-forward to undertake, may miss important details relating to the ways in which environmental stressors interact to influence the performance of organisms, and the ways in which organisms interact to influence the distribution and abundance of species within an ecosystem. I propose to target the linkages between warming and OA, and study their combined influence on individual organisms and on interacting groups of species (communities). At the organismal level, I will test theory that predicts that decreasing pH reduces tolerance of high temperatures. I will also assess the importance of environmental variability, which is often overlooked by researchers focused on changes in typical or average conditions. By using animals that are locally adapted to particular environmental conditions or have been exposed to various combinations of stable or fluctuating conditions, I will also explore the extent to which animals can acclimate or adapt to their environment to avoid particularly damaging consequences of simultaneous warming and acidification. I will then scale this up to interacting pairs of species, be they plants and herbivores, competitors, or hosts and parasites. For example, slight changes in temperature can increase rates of grazer growth and herbivory faster than rate of photosynthesis and plant growth. At some point a tipping point is reached, and consumers can locally eliminate their food source. I will test the sensitivity of this tipping point to changes in other variables, particularly ocean acidification, along with the role of thermal variability in setting the tipping points in the first place. Analogous experiments will examine the sensitivity of competitive and parasitic relationships to simultaneous variation in temperature and ocean acidification. Finally, experiments and field observations on real communities in the wild will determine the degree to which ecological theory can predict the outcome of complex climate change. These results will help resource managers and conservation biologists anticipate when "ecological surprises" might actually be expected, and better understand the role of genetic variability and species diversity in resisting such changes. **