title: Combined physical, chemical and biological factors shape Alexandrium ostenfeldii blooms in The Netherlands.
abstract: Harmful algal blooms (HABs) are globally expanding, compromising water quality worldwide. HAB dynamics are determined by a complex interplay of abiotic and biotic factors, and their emergence has often been linked to eutrophication, and more recently to climate change. The dinoflagellate Alexandrium is one of the most widespread HAB genera and its success is based on key functional traits like allelopathy, mixotrophy, cyst formation and nutrient retrieval migrations. Since 2012, dense Alexandrium ostenfeldii blooms (up to 4500cellsmL-1) have recurred annually in a creek located in the southwest of the Netherlands, an area characterized by intense agriculture and aquaculture. We investigated how physical, chemical and biological factors influenced A. ostenfeldii bloom dynamics over three consecutive years (2013-2015). Overall, we found a decrease in the magnitude of the bloom over the years that could largely be linked to changing weather conditions during summer. More specifically, low salinities due to excessive rainfall and increased wind speed corresponded to a delayed A. ostenfeldii bloom with reduced population densities in 2015. Within each year, highest population densities generally corresponded to high temperatures, low DIN:DIP ratios and low grazer densities. Together, our results demonstrate an important role of nutrient availability, absence of grazing, and particularly of the physical environment on the magnitude and duration of A. ostenfeldii blooms. Our results suggest that predicted changes in the physical environment may enhance bloom development in future coastal waters and embayments.
authors.affiliation: Department of Aquatic Ecology, Netherlands Institute of Ecology, Wageningen, The Netherlands. Electronic address: k.brandenburg@nioo.knaw.nl.
authors.forename: Karen M
authors.initials: KM
authors.lastname: Brandenburg
authors.affiliation: Department of Aquatic Ecology, Netherlands Institute of Ecology, Wageningen, The Netherlands; Aquatic Ecology and Water Quality Management Group, Wageningen University, The Netherlands.
authors.forename: Lisette N de Senerpont
authors.initials: LNS
authors.lastname: Domis
authors.affiliation: Department of Ecological Chemistry, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany.
authors.forename: Sylke
authors.initials: S
authors.lastname: Wohlrab
authors.affiliation: Department of Ecological Chemistry, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany.
authors.forename: Bernd
authors.initials: B
authors.lastname: Krock
authors.affiliation: Department of Ecological Chemistry, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany.
authors.forename: Uwe
authors.initials: U
authors.lastname: John
authors.affiliation: Waterschap Scheldestromen, Middelburg, The Netherlands.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: van Scheppingen
authors.affiliation: Department of Aquatic Ecology, Netherlands Institute of Ecology, Wageningen, The Netherlands.
authors.forename: Ellen
authors.initials: E
authors.lastname: van Donk
authors.affiliation: Department of Aquatic Ecology, Netherlands Institute of Ecology, Wageningen, The Netherlands.
authors.forename: Dedmer B
authors.initials: DB
authors.lastname: Van de Waal
mesh_terms: D001685:Biological Factors / Q000032:analysis*; D057231:Climate Change; D005068:Eutrophication; D057097:Harmful Algal Bloom; D009426:Netherlands; D013696:Temperature
chemical_list: D001685:Biological Factors
keywords: Alexandrium; Grazing; Nutrients; Salinity; Temperature; Wind speed