Factors affecting phytoplankton extracellular release in the Southern Bight of the North Sea

Abstract

Phytoplankton extracellular release of organic substances was studied in the Southern Bight of the North Sea in relation to changes in growth conditions (light intensity and inorganic nitrogen concentration) and in taxonomic phytoplankton composition. Light intensity had no effect on percent extracellular release (PER). A high negative correlation between PER and mineral nltrogen concentration was found during spring bloom when phytoplankton were dominated by flagellates (Phaeocystis poucheti in the Southern Bight; dinoflagellates in the oligotrophic English Channel). The physiological response of the flagellate populations to shortage of nutrients differed. High PER was measured dunng the decline of the bloom with lower values in ollgotrophic (46 %) than eutrophic waters (70 to 80 %). On the other hand, no significant correlation was found between PER and mineral nitrogen for diatoms which dominate the phytoplankton population outside the spring period. PER values were unchangeably low (0 to 14 % ) over a large range of mineral nitrogen concentrations (0 to 50 pg at N I-').

Impact of nitrogen availability upon the electron requirement for carbon fixation in Australian coastal phytoplankton communities

“…Phytoplankton are responsible for the majority of marine primary production (MPP) that fuels ocean ecosystem and climate-relevant biogeochemical cycles (Field et al 1998;Falkowski et al 2004). Predicting how MPP varies over space and time has therefore remained a key goal for oceanographers for over a century, but is still subject to considerable uncertainty (Laufk€ otter et al 2015). This is due to a chronic lack of in situ observational data to support predictive models, particularly for coastal waters, sub-tropical regions and the temperate southern hemisphere (Carr et al 2006;Cheah et al 2011;Everett and Doblin, 2015).…”