Abstract
We propose a new method to simultaneously identify limiting factors for productions of multiple primary producer types in costal planktonic communities. This method combines fatty acid composition analysis with conventional algal growth potential tests in which various combinations of nutrient and metal species are added to coastal waters. For seawater collected from Shizugawa bay in September 2017, it was shown that the production of POC and chlorophyll a were primarily limited by nitrogen. The fatty acid composition analysis indicated that nitrogen addition markedly increased particle productions especially by bacteria or cyanobacteria. Meanwhile, the productions of fatty acid markers of diatoms, dinoflagellates and green algae remarkably increased by phosphorus addition, so production of those algal groups seems to be limited by phosphorus rather than nitrogen. Overall, our method has great potential to bring useful knowledge to help to predict responses of inner bay primary producers to changes in material compositions loaded from watersheds. Concerning the preservability of the marker fatty acid composition, further study is necessary.
