Differences on phyoplankton community responses to acidification and nutrient input’

Supervisor: Shannon L. Meseck (National Oceanic and Atmospheric Administration, Northeast Fisheries Science Center, Milford Laboratory, USA)
Coastal waters often have high phytoplankton abundance and diversity, making coastal ecosystems important areas of productivity. This high productivity introduces biogeochemical, physical, and biological factors which can distinguish coastal ecosystems from open ocean systems in terms of response to climate change. A major concern about climate change is increasing pCO2 levels in seawater and the effects on these productive coastal ecosystems. In coastal areas highly populated by humans, nitrogen pollution (eutrophication) often is an important issue. Acidification might interact with eutrophication in unpredictable ways. To understand the individual and combined effects of acidification and eutrophication upon phytoplankton communities in coastal waters, a 2X2 factorial experiment (n=2 for each treatment) with 2 levels of pCO2 (700μatm and 1500μatm) and 2 levels of nutrient enrichment (10μM and 40μM ),was carried out at ambient temperature for 10 days with water collected on 30 March, 2015, from Long Island Sound (LIS) in Milford, CT, USA. The phytoplankton community was examined for species succession, size differences, carbon, nitrogen, phosphate and silicate (C:N:P:Si) stoichiometry, and quantum yield of fluorescence. Community composition showed no differences between treatments with Skelatonema costatum dominating in all treatments. Growth rate of the entire phytoplankton community was lower in the treatment with increased pCO2 and high nitrogen. These counter-intuitive results suggest that the combination of eutrophication and future pCO2 levels will not necessarily “fertilize” early spring phytoplankton communities, in terms of species composition or overall community growth rates.