pCO2 effects on species composition and growth of an estuarine phytoplankton community

• Published in: Estuarine, Coastal and Shelf Science
• Main Authors: Grear, Jason S., Rynearson, Tatiana A., Montalbano, Amanda L., Govenar, Breea, Menden-Deuer, Susanne
• Format: Text
• Language: unknown
• Published: DigitalCommons@URI 2017
• Subjects: Carbon dioxide; Carbonate chemistry; Cell size; Chemostat; Community; Composition; Ecostat; Incubation; Mesocosm; Ocean acidification; pH; Phytoplankton; Plankton
• Online Access: https://digitalcommons.uri.edu/gsofacpubs/1875; https://doi.org/10.1016/j.ecss.2017.03.016

The effects of ongoing changes in ocean carbonate chemistry on plankton ecology have important implications for food webs and biogeochemical cycling. However, conflicting results have emerged regarding species-specific responses to pCO2 enrichment and thus community responses have been difficult to predict. To assess community level effects (e.g., production) of altered carbonate chemistry, studies are needed that capitalize on the benefits of controlled experiments but also retain features of intact ecosystems that may exacerbate or ameliorate the effects observed in single-species or single cohort experiments. We performed incubations of natural plankton communities from Narragansett Bay, RI, USA in winter at ambient bay temperatures (5–13 °C), light and nutrient concentrations. Three levels of controlled and constant CO2 concentrations were imposed, simulating past, present and future conditions at mean pCO2 levels of 224, 361, and 724 μatm respectively. Samples for carbonate analysis, chlorophyll a, plankton size-abundance, and plankton species composition were collected daily and phytoplankton growth rates in three different size fractions (<5, 5–20, and >20 μm) were measured at the end of the 7-day incubation period. Community composition changed during the incubation period with major increases in relative diatom abundance, which were similar across pCO2 treatments. At the end of the experiment, 24-hr growth responses to pCO2 levels varied as a function of cell size. The smallest size fraction (<5 μm) grew faster at the elevated 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. Similarity in Past and Future treatments for cell size distribution and growth rate (5–20 μm size fraction) illustrate non-monotonic effects ...