Photosynthetic carbon metabolism and biochemical composition of spring phytoplankton assemblages enclosed in microcosms: the diatom- Phaeocystis sp. succession

Abstract

Samples of natural phytoplankton assemblages were taken from two stations SW of Plymouth (UK) and incubated in experimental microcosms under constant light and temperature. Microflagellates which dominated in the first experiments were followed in later experiments by a multispecific bloom of chain-forming diatoms, and these in turn by a bloom of Phaeocystis sp. High 14C incorporation into LMWM and lipids was observed during non-growth periods when microflagellates dominated. High 14C incorporation into proteins and relatively high specific rates of protein synthesis (0.45 ± 0.1 d-1) were measured during the late growth phase of the diatom bloom. Synthesis of acid-soluble carbohydrates also occurred in this period. As Phaeocystis sp. increased, 14C incorporation into low molecular weight metabolites and polysaccharides showed a significant rise. Metabolic changes associated with the diatom-Phaeocystis sp. succession are in accord with a marked shift in the trophic structure of the planktonic ecosystem from the classical food chain in the earlier stages, and mainly during the diatom bloom, to a preponderance of the microbial loop at the end of the Phaeocystis sp. bloom. -from Authors