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UBC Theses and Dissertations

Intraspecific variation mediates response to climate change across environmental gradients in marine systems Emry, Sandra


To better predict the responses of ecological systems to climate change we must better understand how interactions between multiple stressors alter organismal function, how these changes may propagate to the community level, and how these interactions may vary across environmental gradients through time. Here, I address this gap in knowledge, primarily using a macroalgal foundation species, Fucus distichus, and its associated community, with a combination of laboratory and field experiments. First, I conducted a reciprocal transplant experiment with F. distichus from areas of differing thermal regimes and simulated a thermal stress event prior to the occurrence of an extreme heatwave. Results show that thermal history matters, as individuals originating from the cooler site that experienced the initial thermal stress had decreased photosynthetic efficiency and increased bleached thallus tissue as a result of the extreme heatwave. Second, I asked how hyposalinity modulates thermal response of early life stages in F. distichus, and whether this is mediated by historical exposure to hyposaline conditions in the parent generation. I found that hyposalinity had larger impacts on the thermal response in individuals that originated from a high saline vs. a hyposaline environment. Next, I asked how the temporal dynamics of stressors impact the interactive effects of hyposalinity and high air temperature in F. distichus from low vs high salinity regions. I found that hyposalinity reduced growth and caused more bleaching in individuals from both regions regardless of whether stressors were imposed simultaneously or sequentially. Lastly, I investigated the indirect effects of salinity on intertidal community composition through diversity surveys in high and low salinity regions, identifying the salinity tolerance of a subset of key resident species, and manipulating the abundance of grazers in a field study replicated across regions. I show that rocky intertidal shores from regions of disparate salinity regimes host distinct ecological communities, which is likely mediated by salinity-driven differences in herbivore population size and thus grazing pressure. By working across temporal and spatial scales, this research advances our understanding of how multiple stressors interact in a marine foundation species with cascading impacts on associated communities.

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