Impact of Increased Nutrients and Lowered pH on Photosynthesis and Growth of Three Marine Phytoplankton Communities From the Coastal South West Atlantic (Patagonia, Argentina)

Effect of global change variables on the structure and photosynthesis of phytoplankton communities was evaluated in three different sites of the Patagonian coast of Argentina: enclosed bay (Puerto Madryn, PM), estuarine (Playa Unión, PU), and open waters (Isla Escondida, IE). We exposed samples to two contrasting scenarios: Present (nutrients at in situ levels) vs. Future (with lowered pH and higher nutrients inputs), and determined growth and photosynthetic responses after 2 days of acclimation. Under the Future condition phytoplankton growth was higher in the estuarine site compared to those in PM and IE. This effect was the most pronounced on large diatoms. While the increase of photosynthetic activity was not always observed in the Future scenario, the lower photosynthetic electron requirement for carbon fixation (Φe,C = ETR/PmB) in this scenario compared to the Present, suggests a more effective energy utilization. Long-term experiments were also conducted to assess the responses along a 4 days acclimation period in PU. Diatoms benefited from the Future conditions and had significantly higher growth rates than in the Present. In addition, Φe,C was lower after the acclimation period in the Future scenario, compared to the Present. Our results suggest that the availability, frequency and amount of nutrients play a key role when evaluating the effects of global change on natural phytoplankton communities. The observed changes in diatom growth under the Future scenario in PU and IE and photosynthesis may have implications in the local trophodynamics by bottom up control

Photosynthesis and Growth of Temperate and Sub-Tropical Estuarine Phytoplankton in a Scenario of Nutrient Enrichment under Solar Ultraviolet Radiation Exposure

We compared the responses of two estuarine phytoplankton communities, one from a temperate (Chubut River estuary (CH), Argentina) and one from a sub-tropical site (Babitonga Bay (BB), Brazil), in a scenario of nutrient enrichment under solar ultraviolet radiation (UVR) exposure. Seawater samples were exposed in microcosms to two nutrients, ambient vs. enriched, and two radiation conditions, with and without UVR, and exposed to solar radiation for 4 days. We evaluated the short- (PSII photochemistry, during 90 min light and 90 min dark cycles, before and after the 4 days of acclimation) and mid-term effects (growth and taxonomic changes) of the phytoplankton communities. Before acclimation, short-term UVR effects were dominant in CH, whereas in BB, nutrient effects prevailed. Such differences were related to the previous light history of the cells and to the ambient nutrient status. After acclimation, an overall improvement of the photosynthetic performance was observed at both sites, either by reducing the relative inhibition or by increasing the recovery of the effective photochemical quantum yield. Interactive effects of UVR and nutrients on growth at CH were antagonistic, while at BB, no differences were observed between the interactive and the sum of effects. Part of the differences in the mid-term observed responses can be attributed to taxonomic changes, with the CH community dominated by diatoms throughout the experiment, but with a shift from a diatom to a flagellate-dominated community in BB. Temperature differences between both sites might have favored higher growth rates and flagellates dominance in BB under the nutrient enriched conditions.Fil: Villafañe, Virginia Estela. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fundación Playa Unión. Estación de Fotobiología Playa Unión; ArgentinaFil: Jabalera Cabrerizo, Marco. Universidad de Granada; EspañaFil: Erzinger, Gilmar S.. Universidade da Região de Joinville; BrasilFil: Bermejo, Paula. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fundación Playa Unión. Estación de Fotobiología Playa Unión; ArgentinaFil: Strauch, Sebastian Michael. Fundación Playa Unión. Estación de Fotobiología Playa Unión; ArgentinaFil: Valiñas, Macarena Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fundación Playa Unión. Estación de Fotobiología Playa Unión; ArgentinaFil: Helbling, Eduardo Walter. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fundación Playa Unión. Estación de Fotobiología Playa Unión; Argentin