Resolving the bloom dynamics and ecological role of Noctiluca scintillans in the southern North Sea

Abstract

Recently, we found that dinoflagellate Noctiluca scintillans proliferates more frequently and intensively in many regions around the globe, including the North Sea. This organism tolerates rapidly changing conditions, thrives under eutrophication, and exhibits multiple reproductive strategies, leading to intense and rapid blooms, which can affect community composition and productivity. To further investigate the bloom dynamics of this species, and its effects on phytoplankton diversity, we studied Noctiluca and collected data during three cruises in summer 2022 in the southern North Sea with traditional techniques, underwater cameras and remote sensing. We measured unusually high ammonium and phosphate concentrations within dense surface patches, suggesting that Noctiluca acts an essential nutrient recycler during blooms. CPICS (Continuous Plankton Imaging and Classification Sensor) and FlowCam images were analysed with applied machine learning techniques, and revealed phytoplankton community composition, prey types, and intraspecific interactions. Noctiluca’s frequently observed ingestion of diatoms followed by a shift to phosphate-affine dinoflagellates suggests a potentially important role within plankton communities. Through satellite images, the bloom extent was visualized, and associated impacts on local coastal communities could be better estimated. Considering its recent development and great adaptability to changing conditions, Noctiluca might play an increasingly important part within plankton communities.