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Understanding the spatial and temporal preferences of toxic phytoplankton species is of paramount importance in managing and predicting harmful events in aquatic ecosystems. In this study, we addressed the realised niche of the species Alexandrium minutum, Pseudo-nitzschia fraudulenta and P. australis to highlight distribution patterns at different scales and determine possible drivers. To achieve this goal, we developed original procedures coupling niche theory and habitat suitability modelling using abundance data in 4 consecutive steps: (1) estimate the realised niche applying kernel functions, (2) assess differences between the species’ niches as a whole and at the local level, (3) develop habitat and temporal suitability models using niche overlap procedures and (4) explore species temporal and spatial distributions to highlight possible drivers. We used data on species abundance and environmental variables collected over 27 yr (1988-2014), including 139 coastal water sampling sites along the French Atlantic coast. Results showed that the niches occupied by A. minutum and P. australis are very different, although both species exhibit a preference for warmer months. They both respond to decadal summer North Atlantic Oscillation (sNAO) but in an opposite way. P. fraudulenta’s realised niche lies in between that of the 2 other species; it also prefers warmer months but does not respond to decadal sNAO. The Brittany peninsula is now classified as an area of prevalence for the 3 species. The methodology used here will allow us to anticipate species distributions in the event of future environmental challenges resulting from climate change scenarios.

12 pages, 8 figures, 1 table.-- Data availability: Data will be made available on request, Subpolar coastal waters are key hotspots in the global carbon cycle. However, the small-scale distribution of partial pressure of carbon dioxide (pCO2) in these environments and the physical and biological controls underlying this variability are still poorly understood. Here, we examine simultaneous high-resolution spatial measurements of wind speed and pCO2, temperature, salinity, and in-vivo chlorophyll-a fluorescence (chl-a fluo, a proxy of phytoplankton biomass) in surface waters that were obtained during an oceanographic survey in the Argentinian Beagle Channel (subantarctic Atlantic Patagonian) in early fall 2017. The 240 km study transect (centered at 55°S - 67°W) was divided into two zones: (A1) The Beagle Channel innermost portion, semi-enclosed and subject to strong continental influence and (A2) its eastern outlet towards the open Southwest Atlantic. Discrete seawater samples were also collected for apparent oxygen utilization (AOU), nutrients and pH measurements. High-resolution spatial measurements revealed the persistence of pCO2 below atmospheric equilibrium, increasing in median (interquartile range 25–75%) from 314 μatm in the inner Beagle Channel (A1) to 348 μatm towards the adjacent open sea (A2). A decrease in atmospheric CO2 sequestration was associated with an increase in water temperature from 9.5 °C to 10.7 °C, salinity from 30.8 to 32.5, and chl-a fluo from 2.24 to 2.91 mg m−3 along the coastal-offshore gradient. Low AOU and nutrient levels were found in regions inside the channel. Indeed, the relationships between CO2 and temperature or salinity were significantly different from those expected from the theoretical solubility effect, indicating a dominance of metabolic over physicochemical controls on this gas. Moreover, physical factors such as vertical stratification contributed to the variable surface pCO2 values. These findings reveal the existence of short-scale spatial variability of CO2 in the Beagle Channel, improving our understanding of the multiple controls on atmospheric carbon sequestration in extensive subpolar continental shelves, We acknowledge support from the Spanish Government through grants CTM2014-56987-P (VA-DE-RETRO Project) and RTI2018-100844-B-C33 (SAGA project) and also recognize the institutional support of the Spanish Government through the Severo Ochoa Centre of Excellence accreditation (CEX2019-000928-S). This study was funded by grants from the Council for Research and Scientific Development of Brazil (CNPq, 203366/2019-0, 314995/2020-0) and the Research Support Foundation of the State of Rio de Janeiro (E-26/211.329/2021 and E-26/201.118/2022). H.M. and L.C.C. were awarded by CNPq Research Productivity and FAPERJ Scientist of Our State fellowships. L.C.C. was awarded by UERJ/PROCIENCIA fellowship

Populated coastal ecosystems in the NW Mediterranean present three main characteristics that distinguish them from the open water ecosystem: a sea-land interaction, with freshwater influence from river mouths; a shallow seabed, which facilitates the interaction between the euphotic water column and the sediments; and high anthropogenic pressure, due to submarine sewage discharges. As a result, relatively high nutrient concentrations are measured in these ecosystems, with ammonia being an important fraction. These characteristics entail a different scenario from the open water ecosystem. Here, we present the distribution of phytoplankton primary production in the Barcelona coastal waters during summer and winter-spring seasons, by means of photosynthesis-irradiance experiments using the 14C technique. In winter-spring, stratification of the water column may begin earlier than in open water due to freshwater inputs. Therefore, with the water-column slightly stratified, chlorophyll-a and primary production become localised in the surface layers, due to the lower daily irradiance during this season. In these conditions, Total Primary Production (TPP) values measured ranged between 0.27 and 14.52 mgC m− 3 h− 1. As spring progresses and the stratification develops, surface waters tend to become nutrient depleted and nutrients are mainly localised in bottom waters between the thermocline and the seafloor. Under these conditions, high chlorophyll layers develop near the bottom. With the exception of their nutrient enrichment, these structures, referred to as coastal deep chlorophyll maxima, are comparable to the oceanic deep chlorophyll maxima in temperate oligotrophic seas. The nutrient enrichment is the result of the sediment resuspension from the seabed and the presence of sewage water discharged from the submarine outfall. These structures are highly productive (ca. 60% of water column primary production), comparable to the winter-spring bloom, and are sustained throughout the stratified season. In this period, TPP values measured ranged between 0.25 and 9.02 mgC m− 3 h− 1. The primary productivity structures studied play a leading role in processing nutrients from terrestrial sources, thus providing an important ecosystem service.

11 pages, 6 figures, 2 tables, supplementary material https://doi.org/10.1016/j.pocean.2019.05.008, The link between phytoplankton primary production (PPP) and chromophoric dissolved organic matter (CDOM) has been demonstrated indirectly in the laboratory, but not directly in the sea. Here, for the first time, we report a strong link between PPP and CDOM in a study carried out in coastal marine waters around Barcelona (NW Mediterranean) in contrasting seasons. We measured relevant correlations between a CDOM concentration and both PPP (r = 0.89, p < 0.001, n = 16; r = 0.76, p < 0.01, n = 10; and r = 0.68, p < 0.001, n = 26; for summer, winter–spring and both seasons together, respectively) and the specific production rate at optimal light intensity (P ; r = 0.77, p < 0.001, n = 16; r = 0.86, p < 0.01, n = 10; and r = 0.85, p < 0.001, n = 26; for the same seasons). Based on our findings, we design a model that predicts PPP very well, using a CDOM, water temperature and photosynthetically active radiation (PAR)(R = 0.84, p < 0.001, n = 26). Relationships between CDOM concentration parameters (measured at wavelengths of 280, 300, 340, 355, 375, 412 and 460 nm) and variables associated to CDOM processes (chlorophyll-a, bacterial abundance, turbidity related to sediment resuspension and PAR) were also evaluated. Bacterial abundance is significantly correlated with CDOM concentration measured at higher wavelengths when all samples are considered (e.g., r = 0.82, p < 0.001, n = 26, for a CDOM). However, in seasonal data analysis, the correlations decrease slightly (summer season: e.g., r = 0.79, p < 0.001, n = 16, for a CDOM) or become non-significant (winter–spring season: e.g., r = -0.02, p = 0.95, n = 10, for a CDOM). Sunlight photobleaching and sediment resuspension processes significantly influence CDOM dynamics in the summer (for a CDOM: r = -0.72, p < 0.001, n = 16; and r = 0.67, p < 0.01, n = 16, respectively), This work was supported by the Catalan Water Agency (Departament de Medi Ambient i Habitatge, Generalitat de Catalunya) through its Monitoring and Control Program (PSIC) of Catalan coastal waters