Abstract
Calcifying haptophytes (coccolithophores) se- quester carbon in the form of organic and inorganic cel- lular components (coccoliths). We examined the effect of phosphorus (P) limitation and heat stress on particulate or- ganic and inorganic carbon (calcite) production in the coc- colithophore Emiliania huxleyi. Both environmental stressors are related to rising CO2 levels and affect carbon production in marine microalgae, which in turn impacts biogeochemi- cal cycling. Using semi-continuous cultures, we show that P limitation and heat stress decrease the calcification rate in E. huxleyi. However, using batch cultures, we show that dif- ferent culturing approaches (batch versus semi-continuous) induce different physiologies. This affects the ratio of partic- ulate inorganic (PIC) to organic carbon (POC) and compli- cates general predictions on the effect of P limitation on the PIC / POC ratio. We found heat stress to increase P require- ments in E. huxleyi, possibly leading to lower standing stocks in a warmer ocean, especially if this is linked to lower nutri- ent input. In summary, the predicted rise in global temper- ature and resulting decrease in nutrient availability may de- crease CO2 sequestration by E. huxleyi through lower overall carbon production. Additionally, the export of carbon may be diminished by a decrease in calcification and a weaker coc- colith ballasting effect.
Phosphorus limitation and heat stress decrease calcification in Emiliania huxleyi