Quantification of multiple environmental controls on lipid biomarkers in common marine diatoms and dinoflagellates

Abstract Ocean-related global changes have altered phytoplankton community structure, especially the diatom-dinoflagellate competition, which further influences ecosystem structure and functions. The pivotal ecological roles of diatoms and dinoflagellates are strongly related with their biochemical compositions, while quantitative comparisons of biochemical changes between diatoms and dinoflagellates under variable environments are still limited. We investigated responses of lipid biomarkers (sterols and fatty acids (FAs)) to different temperatures (12, 18 and 24℃), nitrogen and phosphorus concentrations and their molar ratios (N:P ratio) of 10:1, 24:1 and 63:1 in marine diatom Phaeodactylum tricornutum and dinoflagellate Prorocentrum minimum. Over these wide ranges of temperature and nutrient conditions, sterol and FA profiles were relatively stable in the two species. For C-normalized contents of major sterols and FAs, warming caused non-significant changes in the diatom but an increase (up to 153%) in the dinoflagellate; eutrophication caused an overall decrease (up to 53%) in the diatom but an overall increase (up to 77%) in the dinoflagellate; in contrast, imbalanced N:P ratios caused an overall increase (up to 64%) in the diatom but an overall decrease (up to 53%) in the dinoflagellate. Under future ocean warming, eutrophication and imbalanced N:P ratios, major sterol and polyunsaturated FA contents would increase (ca. 9% ~ 48%) in the dinoflagellate, while those in the diatom would change non-significantly. This study expands our knowledge on lipid-based indicators of phytoplankton under changing environments, which by systematically linking with several other aspects of food quality will help to understand the ecological role of diatom-dinoflagellate community changes.