COMBINED EFFECTS OF TEMPERATURE AND CO2 CONCENTRATION ON THE GROWTH AND CHEMICAL COMPOSITION OF MARINE PHYTOPLANKTON Nannochloropsis oculata AND Chaetoceros gracilis

Algae, the most abundant primary producers in the ocean, are organisms capable of transforming inorganic nutrients into organic matter through photosynthesis. As primary producers, they are the first trophic level in the ocean food chain and serve as a food source for consumers at higher trophic levels. To produce organic compounds, such as carbohydrates, lipids, and proteins, algae utilize dissolved CO₂. Hence, their physiology is influenced by ocean acidification and rising ocean temperatures. As temperature and CO₂ concentration change, algal cells chemically adapt to the environment producing biomass with differing chemical compositions. Temperature strongly influences algae cellular chemical composition, uptake of nutrients and CO₂, and productivity. Changes in CO₂ concentrations affect algae growth, lipid formation, productivity, and species composition. The objective of this study is to determine the independent and combined effects of various CO₂ concentration and temperature levels on the growth and chemical/nutritional composition (lipid, protein and carbohydrate content) of two marine phytoplankton species important to Northern California: Nannochloropsis oculata and Chaetoceros gracilis to further understand their impacts on primary consumers.

Mimicking projected conditions for the temperature and CO₂ levels in Northern California, where the majority of oyster farms in California are, algae will be grown in two different temperatures (10°C and 18°C) and at two different pH (8.1 and 7.8). These treatments bracket the present and projected conditions for 2100, by the Intergovernmental Panel on Climate Change (IPCC), to determine the combined effects of ocean acidification and temperature on their growth and chemical composition. Growth, lipid, protein and carbohydrate content will be analyzed for each condition. The results from this study will be used to understand the impacts of changes in primary producers, like algae, on primary consumers, like oysters, which correspond to the first and second trophic levels, respectively, in the ocean.