Global increases in atmospheric CO2 are acidifying the ocean (ocean acidification) and altering seawater chemistry. This is expected to directly influence marine communities by impacting organism physiology. Less is known, however, about how ocean acidification may indirectly affect the productivity of marine food webs by altering the biomass and nutritional quality of primary producers at the base of the food chain. As the oceans absorb atmospheric CO2, concentrations of dissolved inorganic carbon (DIC) increase. This, in turn, can stimulate algal production (food quantity) and alter algal nutrient stoichiometry and lipid composition (food quality). Consequently, ocean acidification may influence the efficiency of carbon (i.e., energy) transfer between primary producers and herbivores, with effects propagating up the food chain.
We propose to experimentally test the effects of rising CO2 levels on carbon transfer efficiency from natural algal communities to multi-species assemblages of herbivorous benthic invertebrates (e.g., amphipods and isopods). This research will advance the understanding of ocean acidification effects on food webs by (1) examining responses in natural assemblages of microalgae and grazers, rather than focusing on individual model species; and (2) gaining a mechanistic understanding of CO2 effects on trophic transfer by quantifying changes in nutrient stoichiometry and essential lipid composition. The experiment will be conducted in a flow-through mesocosm system that automatically controls the CO2 concentrations and carbonate chemistry of natural seawater. Testing and validating the automatic CO2-controlling system, that we designed, are key components of this proposal. Environmentally realistic mesocosm experiments are one of the best ways to mechanistically understand ecological processes and expanding an existing mesocosm system to control seawater carbonate chemistry will increase WHOI’s capacity to quantify the impacts of ocean acidification.
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