Responses of marine diatom-dinoflagellate competition to multiple environmental drivers: abundance, elemental and biochemical aspects

A key challenge in ecology and biogeochemistry is to quantitatively determine the effects of multiple environmental factors on the diatom-dinoflagellate community and the related changes in elemental and biochemical composition. Here, laboratory experiments were conducted to investigate the responses of a diatom-dinoflagellate community to the interactions between temperature, N and P concentrations and their ratios. In particular, we focus on quantitatively assessing the changes in elemental stoichiometry and lipid biomarkers associated with the shifts of community composition. The phytoplankton species used in the experiments were the diatom Phaeodactylum tricornutum and the dinoflagellate Prorocentrum minimum. Both monocultures and bicultures of the two species were exposed to a fully factorial combination of three temperatures (12, 18 and 24°C), three N:P supply ratios (molar ratios 10:1, 24:1 and 63:1) and three nutrient concentration levels in temperature-controlled cabinets. Algal cells were harvested at steady state in semi-continuous cultures. The following parameters were analyzed: Cell density, POC, PON, POP, FAs and sterols.