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Phytoplankton community response to carbon dioxide enrichment in winter incubation experiments
Grear, J., T. Rynearson, A. Montalbano, B. Govenar, AND S. Menden-Deuer. Phytoplankton community response to carbon dioxide enrichment in winter incubation experiments. Coastal and Estuarine Research Federation (CERF) 23rd Biennial Conference, Portland, OR, November 08 - 12, 2015.
This presentation abstract describes research that describes estuarine biological responses to nutrient-enhanced coastal acidification, which is a research theme in the SSWR planning for FY16-19.
Coastal waters are experiencing changes in carbonate chemistry, including pH, in response to increases in atmospheric CO2 concentration and the microbial degradation of surplus organic matter associated with nutrient enrichment. The effects of this change on plankton communities have important implications for food webs and carbon fixation in surface waters. However, conflicting results have emerged regarding responses of phytoplankton species and communities to experimental CO2 enrichment. To explain these differences, experiments are needed that capitalize on the benefits of controlled experiments but conserve and assess potentially confounding or ameliorating features of intact ecosystems. We performed winter “ecostat” incubations of natural plankton communities from lower Narragansett Bay at ambient bay temperatures (5-13 C), light and nutrients under three levels of CO2 enrichment simulating past, present and future conditions (mean pCO2 levels were 224, 361, and 724 uatm). Growth rates for size fractions (<5, 5-20, and >20 um) were estimated at the end of the 7-day incubation period; samples for carbonate analysis, chlorophyll a, plankton size-abundance, and plankton species composition were collected daily. Community composition changed during the incubation with major increases in diatom abundance, which were similar across treatments. pCO2 treatments caused significant differences in growth rates for the 5-20 um size fraction and in the power law relationship between cell size and cell abundance. However, the 5-20 um growth rate was highest in the past and future treatments, as was the shift in cell size abundance toward smaller cells. These non-monotonic effects of increasing pCO2 may be related to opposing physiological effects of high CO2 vs low pH both within and among species. Interaction of these effects with other factors (e.g., nutrients, light, temperature, grazing, initial species composition) may explain variability among published studies.