Marine N₂ fixing microorganisms, termed diazotrophs, are a key functional group in marine pelagic ecosystems. The biological fixation of dinitrogen (N₂) to bioavailable nitrogen provides an important new source of nitrogen for pelagic marine ecosystems and influences primary productivity and organic matter export to the deep ocean. As one of a series of efforts to collect biomass and rates specific to different phytoplankton functional groups, we have constructed a database on diazotrophic organisms in the global pelagic upper ocean by compiling about 12 000 direct field measurements of cyanobacterial diazotroph abundances (based on microscopic cell counts or qPCR assays targeting the nifH genes) and N₂ fixation rates. Biomass conversion factors are estimated based on cell sizes to convert abundance data to diazotrophic biomass. The database is limited spatially, lacking large regions of the ocean especially in the Indian Ocean. The data are approximately log-normal distributed, and large variances exist in most sub-databases with non-zero values differing 5 to 8 orders of magnitude. Reporting the geometric mean and the range of one geometric standard error below and above the geometric mean, the pelagic N₂ fixation rate in the global ocean is estimated to be 62 (52–73) Tg N yr⁻¹ and the pelagic diazotrophic biomass in the global ocean is estimated to be 2.1 (1.4–3.1) Tg C from cell counts and to 89 (43–150) Tg C from nifH-based abundances. Reporting the arithmetic mean and one standard error instead, these three global estimates are 140 ± 9.2 Tg N yr⁻¹, 18 ± 1.8 Tg C and 590 ± 70 Tg C, respectively. Uncertainties related to biomass conversion factors can change the estimate of geometric mean pelagic diazotrophic biomass in the global ocean by about ±70%. It was recently established that the most commonly applied method used to measure N₂ fixation has underestimated the true rates. As a result, one can expect that future rate measurements will shift the mean N₂ fixation rate upward and may result in significantly higher estimates for the global N₂ fixation. The evolving database can nevertheless be used to study spatial and temporal distributions and variations of marine N₂ fixation, to validate geochemical estimates and to parameterize and validate biogeochemical models, keeping in mind that future rate measurements may rise in the future. The database is stored in PANGAEA (doi:10.1594/PANGAEA.774851).

This study reviews the trends in the lifestyle, habitat distribution and trophic diversity of the 2377 described species of dinoflagellates (Dinophyceae). Most of the dinoflagellates inhabit marine waters, whereas 17% of the total species have colonized continental waters. Dinoflagellates are dominated by planktonic species, while benthic forms represented 8% of the species. From the total number of species, 49% are heterotrophic (devoid of plastids), while 51% of the species have been reported with plastids (that does not strictly imply autotrophy). All the basal dinoflagellates (ellobiopsids, Duboscquodinida, Syndiniales) are heterotrophic, with the exception of a few Noctilucales (Spatulodinium). The continental waters are highly dominated by plastid-containing species (88%), while in marine environments there is a slight dominance of heterotrophic species (58%). Most of the dinoflagellates are free-living forms; only 7% of the total species are parasites. The dinokaryotic parasites appear in separate clades, and about 40% of them contain plastids. The beneficial or mutualistic symbionts (21 species, 1%) are photosynthetic species dispersed into at least three clades.

A checklist and classification of the extant dinoflagellates are given. Dinokaryotic dinoflagellates (including Noctilucales) comprised 2,294 species belonging to 238 genera. Dinoflagellatessensu lato(Ellobiopsea, Oxyrrhea, Syndinea and Dinokaryota) comprised 2,377 species belonging to 259 genera. The nomenclature ofseveral taxa has been corrected according to the International Code of Botanical Nomenclature. When gene sequences were available, the species were classified following the Small and Large SubUnit rDNA (SSU and LSU rDNA) phylogenies. No taxonomical innovations are proposed herein. However, the checklist revealed that taxa distantly related to the type species of their genera would need to be placed in a new or another knowngenus. At present, the most extended molecular markers are unable to elucidate the interrelations between the classical orders, and the available sequences of other markers are still insufficient. The classification of the dinoflagellates remains unresolved, especially at the order level.

The marine epiphytic dinoflagellate Gambierdiscus is a toxicologically important genus responsible for ciguatera fish poisoning, the principal cause of non-bacterial illness associated with fish consumption. The genus currently contains species exhibiting either globular or anterior-posteriorly compressed morphologies with marked differences in cell shape and plate arrangement. Here we report a third globular, epiphytic and tychoplanktonic species from the coasts of Ubatuba, Brazil. The new species can be distinguished from G. yasumotoi and G. ruetzleri by its broader first apical plate that occupies a larger portion of the epitheca. Accordingly, phylogenetic trees from small subunit (SSU) and large subunit (LSU) ribosomal DNA sequences also showed strongly supported separation of the new species from the G. yasumotoi / G. ruetzleri group albeit with short distance. The molecular phylogenies, which included new sequences of the planktonic species Goniodoma polyedricum, further indicated that the globular species of Gambierdiscus formed a tight clade, clearly separated (with strong bootstrap support) from the clade of lenticular species including the type for Gambierdiscus. The morphological and molecular data in concert support the split of Gambierdiscus sensu lato into two genera. Gambierdiscus sensu stricto should be reserved for the species with lenticular shapes, highly compressed anterioposteriorly, with short-shank fishhook apical pore plate, large 2' plate, low and ascending cingular displacement, and pouch-like sulcal morphology. The new genus name Fukuyoa gen. nov. should be applied to the globular species, slightly laterally compressed, with long-shank fishhook apical pore plate, large 1' plate, greater and descending cingular displacement, and not pouch-like vertically-oriented sulcal morphology. Fukuyoa contains the new species Fukuyoa paulensis gen. et sp. nov., and F. yasumotoi comb. nov. and F. ruetzleri comb. nov.

The disproportionately low presence of marine species in the list of invasive alien species (IAS) of Union concern of the European Union (EU) Regulation 1143/2014 does not fully acknowledge the threat they pose to the EU marine environment. In this study, the first EU‐scale Horizon Scanning (HS) focusing on marine alien species was performed, aiming to deliver a ranked list of species that should be of high priority for risk assessment (Article 5 of the EU IAS Regulation). Species absent from or with a limited distribution in EU marine waters were targeted. In total, 363 alien species were initially screened for HS by a panel of experts, including a broad range of taxonomic groups. Species were scored for their likelihood of arrival, establishment, spread, and impact in EU waters. A consensus workshop ranked 267 species, including a subset of 26 prioritized species. These species are considered to be mainly introduced by shipping (fouling and ballast water), via the Suez Canal, and aquaculture activities. The 26 priority species were also scrutinized in terms of feasibility of their management; 18 of them were suggested for performing risk assessments on the basis of the EU IAS Regulation. Since biological invasions are dynamic and connected with accelerated globalization and diversified human activities, we recommend HS to be repeated periodically to review the species already listed and assess new ones.

Abundance and composition of microplankton were studied over a period of 2 years at two depths in Villefranche Bay (Ligurian Sea, NW Mediterranean Sea). Diatoms dominated the microplankton in late spring and autumn, whereas dinoflagellates composed the major part of the microplankton in summer. The silicoflagellate Dictyocha fibula and the diatom Thalassionema frauenfeldii dominated in winter. Ciliates showed low variability throughout the year with the lowest abundance in February and an increase which coincided with the diatom maxima during autumn in both years. In 1998, the spring bloom (in May) was mainly composed of dinoflagellates near the surface and of diatoms in deeper layers. Subsurface diatom maxima were observed in August–September and November. In 1999, diatoms peaked in May both at the surface and at the depth of 50 m. They showed a strong maximum in October. Dinoflagellates and tintinnids showed maxima in early November. Comparisons with previous studies reveal that (i) changes in species composition have not been significant, (ii) the silicoflagellate’s abundance is lower during the present study, (iii) the sequential spring bloom is composed of a pico-nanoplankton bloom in March and microphytoplankton in May, whereas in other western Mediterranean areas the spring microphytoplankton bloom is reported in February and March, (iv) high water transport through the Corsica channel coinciding with low or negative winter values of North Atlantic Oscillation (NAO) index are associated with the anomalous strong development of the spring diatom blooms in the Bay of Villefranche, whereas the usual trend is the lack of or weak development of the spring diatom bloom. This feature may determine the nature and the fate of primary production and the interannual variability in the relative importance of the microbial food web versus the microbial loop.