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PCO2 effects on species composition and growth of an estuarine phytoplankton community
Citation:
Grear, J., T. Rynearson, A. Montalbano, B. Govenar, AND S. Menden-Deuer. PCO2 effects on species composition and growth of an estuarine phytoplankton community. Association for the Sciences of Limnology and Oceanography (ASLO) Ocean Sciences Meeting, New Orleans, LA, February 21 - 26, 2016.
Impact/Purpose:
This presentation abstract describes research that focusing on estuarine biological responses to nutrient-enhanced coastal acidification, which is a research theme in the SSWR planning for FY16-19.
Description:
Ocean and coastal waters are undergoing changes in carbonate chemistry, including pH, in response to increasing atmospheric CO2 concentration and the microbial degradation of organic matter associated with nutrient enrichment. The effects of this change on plankton communities have important implications for food webs and biogeochemical cycling. However, conflicting results have emerged regarding responses of phytoplankton species and communities to experimental CO2 enrichment. 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). Major increases in relative diatom abundance occurred during the experiment but were similar across pCO2 treatments. At the end of the experiment, 24-hr growth responses to pCO2 varied as a function of cell size. The smallest size fraction (<5 µm) grew faster at the Future pCO2 level. In contrast, the 5-20 µm size fraction grew fastest in the Present treatment and there were no significant differences in growth rate among treatments in the > 20 µm size fraction. Cell size distribution shifted toward smaller cells in both the Past and Future treatments but remained unchanged in the Present treatment. 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. The absence of clear treatment-specific effects at the community level suggest that extrapolation of species-specific responses would produce misleading predictions of ocean acidification impacts on plankton production.