Eco-physiological adaptation shapes the response of calcifying algae to nutrient limitation.

The steady increase in global ocean temperature will most likely lead to nutrient limitation in the photic zone. This will impact the physiology of marine algae, including the globally important calcifying coccolithophores. Understanding their adaptive patterns is essential for modelling carbon production in a low-nutrient ocean. We investigated the physiology of Helicosphaera carteri, a representative of the abundant but under-investigated flagellated functional group of coccolithophores. Two strains isolated from contrasting nutrient regimes (South Atlantic and Mediterranean Sea) were grown in phosphorus-replete and phosphorus-limited batch cultures. While growing exponentially in a phosphorus-replete medium, the Mediterranean strain exhibited on average 24% lower growth rate, 36% larger coccosphere volume and 21% lower particulate inorganic carbon (PIC) production than the Atlantic strain. Under phosphorus limitation, the same strain was capable of reaching a 2.6 times higher cell density than the Atlantic strain due to lower phosphorus requirements. These results suggest that local physiological adaptation can define the performance of this species under nutrient limitation.