Long-term changes in spatiotemporal distribution of Noctiluca scintillans in the southern North Sea

To assess the spatiotemporal evolution of the heterotrophic dinoflagellate Noctiluca scintillans in the North Sea, the Helgoland Roads time series and Continuous Plankton Recorder survey were analysed using generalized additive models. Over the last decades, blooms of N. scintillans have occurred more frequently and intensively in many regions. This harmful algal bloom forming species can alter food webs, reduce ecosystem productivity, and lead to economic losses while causing lower aquacultural yields. After the 1990s, N. scintillans abundances have significantly increased by 1.65-fold and a significant prolongation of the bloom window was found (from 27.5 to 98 days in recent decades) off the island of Helgoland, Germany. Significant correlations were found between bloom initiation and nutrients, as well as light availability since these factors lead to increased prey availability. Highest abundances of N. scintillans were associated with water temperatures around 17 °C and wind speed below 6 ms