| Summary: | Marine life is currently under threat from large-scale, long-term changes to the marine environment. Anthropogenic emissions of greenhouse gases, particularly carbon dioxide (CO₂), are causing ongoing change to global marine systems, particularly through ocean warming and acidification. Greenhouse gases in the atmosphere are trapping radiation and heating the entire Earth surface, including the ocean. At the same time, oceanic uptake of CO₂ through absorption by surface waters is altering ocean chemistry, increasing acidity, reducing availability of carbonate ions (CO₃²⁻), and causing increasing dissolution of calcium carbonate (CaCO₃) structures. Because atmospheric CO₂ diffuses more readily into cold water, the Southern Ocean (SO) will experience ocean acidification in a matter of decades. Warming in the SO is also occurring rapidly and represents a comparatively greater increase in temperature than elsewhere. SO marine fauna have evolved in constant, stable, cold conditions, and as a result are stenothermal and particularly at risk from ocean warming and acidification. The large infaunal bivalve Laternula elliptica is a prevalent keystone species found throughout the Antarctic benthos in high numbers, and contributes significantly to biodeposition and bentho-pelagic coupling. This thesis examines how L. elliptica adults are affected over medium-term (5-mo) timescales by SO warming and acidification. Adult L. elliptica collected from Cape Evans in McMurdo Sound, Antarctica, were subjected to combinations of temperatures and pHs predicted for the SO by 2050 and 2100 (Temperatures: -1.4°C (control); -0.5°C; +0.5°C. pHs: pH 8.00 (control); pH 7.85; pH 7.65). L. elliptica were assessed at 5 wk and 5 mo to determine their cellular, metabolic, and whole-organism responses to temperature increase and/or pH decrease. Survival parameters such as final survival percentage, survival curves, and time to 50% survival (LD₅₀) were compared among treatments. L. elliptica survival was severely reduced by warming of only 1-2°C ...
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