The utilization of organic nutrients in marine phytoplankton with emphasis on coccolithophores

This thesis investigated the ability of marine phytoplankton (especially coccolithophores) to utilize organic nutrients and the influence of CO2-induced changes of environmental conditions like a decreased ratio of inorganic to organic nutrients on a phytoplankton community.A North Atlantic phytoplankton assemblage showed no effect on the composition of the assemblage under a changed ratio of inorganic to organic nutrients, but some diatom genera preferred inorganic or organic nutrients. The ability of genera to utilize organic nutrients indicates a competitive advantage of these genera compared to inorganic nutrient preferring genera when organic nutrients are available.Three coccolithophores were grown on seven different organic nutrient compounds to investigate if the utilization of organic nutrient compounds is species-specific. All three coccolithophores were able to utilize a range of different organic nutrients, but two species did not grow on some organic nutrients. This disability could indicate their dependence on nitrate and phosphate and lead to a competitive advantage over other species which are able to utilize these organic nutrients.The results of this thesis are a further step to understand the utilizability and importance of organic nutrients in the ocean. Species which are not able to utilize organic nutrients may be nitrogen or phosphorus limited under a decreased inorganic to organic nutrient ratio. These limitations may affect silicification and calcification and therefore change biogeochemical cycles.