Evelyn Armstrong (1)* and Cliff S. Law (2,3)
1 NIWA/University of Otago Research Centre for Oceanography, Department of Chemistry, University of Otago, Dunedin, 9016, New Zealand
2 National Institute of Water and Atmospheric Research, Greta Point, Kilbirnie, Wellington 6002, New Zealand
3 Department of Chemistry, University of Otago, Dunedin, 9016, New Zealand
Climate change and ocean acidification will have major impacts on marine ecosystems and biogeochemical cycles. This will be partly dependent on the response of phytoplankton to future change as they occupy a key role in the cycling of nutrients and carbon. Current research has identified significant changes in growth rate, metabolic processes and nutrient cycling in phytoplankton that may arise in response to increasing temperature and CO2. However, the majority of studies to date have been relatively short-term and so do not consider the potential of phytoplankton to adapt to changing temperature and CO2.
We are investigating the effect of long term changes in temperature and pH on two New Zealand phytoplankton, a Pseudonitzschia sp. and an E. huxleyi strain, isolated from subantarctic water, by incubating cultures in conditions representing current and future conditions projected for the end of this century (0.3 – 0.4 decrease in pH, 3 oC increase in temperature). The pH of the future culture medium is set using 10% CO2 prior to cells being added, and maintained in all cultures by continuous supply to the headspace of air mixtures with CO2 levels at 380 ppm for current conditions or 750 ppm for future conditions. Cells from the first cultures were harvested to provide baseline values and cell parameters, with follow-up analysis after 4 – 5 months incubation (110 – 120 generations). In addition, cells were cross – inoculated from current to future conditions, and vice versa, to examine adaptation potential.
Preliminary results indicate changes in diatom growth rate and size whereas cellular chlorophyll remained constant in both treatments, with cellular phosphate increasing under future conditions. Current and future results will be assessed in terms of the implications for future biogeochemical cycles and phytoplankton composition.