Evolution of phytoplankton community structure and physiology in a newly-upwelled filament off Pt. Sur, Central California

In the summer of 2019 the CCE-LTER program studied the evolution of a filament of Pt. Sur, Central California. The filament's source waters were recently upwelled water high in nutrients and low in phytoplankton biomass. From the coastal areas the filament flowed towards the south-west then south, to be drawn eventually into a front between the coastal waters and the California current. The filament was followed using quasi-lagrangian drifters over two weeks. Phytoplankton community structure was assessed using sizefractionation of Chl a, taxon-specific pigments analyzed by HPLC and advanced laser fluormetry (ALF). The physiology of the phytoplankton was assessed using FRRF and measurements of primary production using the 14C method. During the course of the study we observed a phytoplankton bloom dominated by large diatoms. The decline of the bloom was primarily due to the removal of the diatoms from the system; other groups of algae did not respond as dramatically. The photosynthetic capacity of the phytoplankton rose during the bloom and subsequently declined, even though nitrate was still replete. We discuss how the temporal response of the plankton mirrors spatial gradients of phytoplankton biomass and community structure that were observed during CalCOFI cruises.