This study evaluated water quality, nitrogen (N), and phytoplankton assemblage linkages along the western Long Island Sound (USA) shoreline (Nov. 2020-Dec. 2021) following COVID-19 stay-in-place (SIP) orders through monthly surveys and N-addition bioassays. Ammonia-N (AmN; NH3+NH4+) negatively correlated with total chlorophyll-a (chl-a) at all sites; this was significant at Alley Creek, adjacent to urban wastewater inputs, and at Calf Pasture, by the Norwalk River (Spearman rank correlation, p < 0.01 and 0.02). Diatoms were abundant throughout the study, though dinoflagellates (Heterocapsa, Prorocentrum), euglenoids/cryptophytes, and both nano- and picoplankton biomass increased during summer. In field and experimental assessments, high nitrite + nitrate (N + N) and low AmN increased diatom abundances while AmN was positively linked to cryptophyte concentrations. Likely N + N decreases with presumably minimal changes in AmN and organic N during COVID-19 SIP resulted in phytoplankton assemblage shifts (decreased diatoms, increased euglenoids/cryptophytes), highlighting the ecological impacts of N-form delivered by wastewater to urban estuaries.

Light microscopy, FlowCam, and sandwich hybridization assay (SHA) are three approaches that facilitate the monitoring of harmful algal bloom (HAB) forming phytoplankton. Yet, cross-comparisons among these techniques have not been conducted. This study addressed that gap using the saxitoxin-producing 'red tide' dinoflagellate Alexandrium catenella, a species responsible for blooms and paralytic shellfish poisoning worldwide. To achieve this goal, the dynamic ranges of each technique were compared using A. catenella cultures spanning low (pre-bloom), moderate (bloom), and high (dense bloom) levels. To assess field detection, water samples containing very low (<3 cells mL-1) A. catenella levels were collected from Long Island Sound, USA (Jun-Aug 2021) and evaluated using each method. Field samples were also spiked with A. catenella to high (160 cells mL-1) or low (40 cells mL-1) concentrations. In general, microscopy, FlowCam, and SHA returned comparable A. catenella cell concentrations for all tests. Mean cell concentrations from laboratory intercalibration experiments were not significantly different for any method or concentration (ANOVA, p > 0.05). However, relative to microscopy at times SHA produced non-detect signals <2 cells mL-1 in field samples and the FlowCam slightly underestimated cell concentrations when A. catenella abundances were high in laboratory and field samples. Mean cell concentrations of spike experiments were not significantly different for any test date, sampling location, or method, despite variability among methods within the high concentration treatment (ANOVA, p > 0.05 for all treatments). Findings are relevant to HAB researchers, managers, and public health officials because they help reconcile disparate cell abundance datasets that inform numerical models and enhance HAB monitoring and prediction. Results are also likely broadly applicable to several HAB species.

Cyanobacteria are an important part of phytoplankton communities, however, they are also known for forming massive blooms with potentially deleterious effects on recreational use, human and animal health, and ecosystem functioning. Emerging high-frequency imaging flow cytometry applications, such as Imaging FlowCytobot (IFCB), are crucial in furthering our understanding of the factors driving bloom dynamics, since these applications provide community composition information at frequencies impossible to attain using conventional monitoring methods. However, the proof of applicability of automated imaging applications for studying dynamics of filamentous cyanobacteria is still scarce. In this study we present the first results of IFCB applied to a Baltic Sea cyanobacterial bloom community using a continuous flow-through setup. Our main aim was to demonstrate the pros and cons of the IFCB in identifying filamentous cyanobacterial taxa and in estimating their biomass. Selected environmental parameters (water temperature, wind speed and salinity) were included, in order to demonstrate the dynamics of the system the cyanobacteria occur in and the possibilities for analyzing high-frequency phytoplankton observations against changes in the environment. In order to compare the IFCB results with conventional monitoring methods, filamentous cyanobacteria were enumerated from water samples using light microscopical analysis. Two common bloom forming filamentous cyanobacteria in the Baltic Sea, Aphanizomenon flosaquae and Dolichospermum spp. dominated the bloom, followed by an increase in Oscillatoriales abundance. The IFCB results compared well with the results of the light microscopical analysis, especially in the case of Dolichospermum . Aphanizomenon biomass varied slightly between the methods and the Oscillatoriales results deviated the most. Bloom formation was initiated as water temperature increased to over 15°C and terminated as the wind speed increased, dispersing the bloom. Community shifts were closely related to movements of the water mass. We demonstrate how using a high-frequency imaging flow cytometry application can help understand the development of cyanobacteria summer blooms.

(1) abstract The paradigm of blue oligotrophic Mediterranean waters with modest increase in productivity as a response to seasonal enrichment produced by water column mixing or to mesoscale structures, such as fronts and gyres, is not widely applicable. The inner-shelf waters are relatively uncoupled from open ocean processes representing a well differentiated niche, where nutrient levels are relatively high and high-biomass microalgal blooms tend to occur (Flo et al. 2011). Several factors define this singularity including strong seasonal stratifi -cation, generally weak and variable currents, and a microtidal regime. The biogeochemical contrast between the culturally enriched inner-shelf waters and the oligotrophic conditions prevailing further offshore is The estimation of species-specific in situ growth rates (µ) is one of the fundamental parameters to understand population dynamics. The in situ growth rate is determi-ned by intrinsic genetic factors, as well as by environ-mental conditions (e.g. light,

Poster presented at the Microscale Ocean Biophysics, held on Jan 11-16th 2019, in Whistler, Canada.

The regional circulation in the northwestern Gulf of Mexico during late spring-summer is modulated by upwelling-favorable winds that can cause coastal upwelling in the western region and by freshwater inputs from the Mississippi-Atchafalaya Rivers. Spatial variability and temporal dynamics of phytoplankton community composition were examined during two upwelling-favorable periods using data obtained with an Imaging FlowCytobot (IFCB) from two cruises on the Texas-Louisiana shelf in June 2013 and 2014 and from the Texas Observatory for Algal Succession Time series (TOAST) at Port Aransas (Texas). Phytoplankton spatial distributions were determined by the influence of upwelling and river discharged waters. In the 2013 cruise, upwelling was detected in a large portion of the western region and the phytoplankton assemblages were dominated by diatoms, mostly chain-forming taxa. As revealed by the TOAST time series, the upwelling onset caused a dramatic increase in diatom carbon biomass. In the areas not affected by upwelling, variation in the river plume distribution that resulted from the circulation and the different discharge magnitudes for each year influenced the spatial distributions of the phytoplankton community composition. Dinoflagellates and other flagellated taxa were notably dominant during the 2013 cruise, whereas both diatoms and flagellated groups dominated the assemblages during the 2014 cruise. High stratification promoted by freshwater input, notably higher during 2013 than 2014, likely favored the dominance of flagellated groups in 2013. This study provides evidence of the influence of coastal upwelling in the phytoplankton community of the northwestern Gulf of Mexico and contributes to the knowledge of the drivers of community composition in this high-productivity area.

Finding a partner in an inherently unsteady 3-dimensional system, such as the planktonic marine environment, is a difficult task for nonswimming organisms with poor control over their orientation. We experimentally investigate the process of cell pairing in pennate marine diatoms and present field evidence of its occurrence in the ocean. We describe the mechanism as a 3-step process in which pennate diatoms (i) vertically reorient while sinking from surface turbulent waters to a more stable environment (i.e., under the seasonal pycnocline), (ii) segregate from incompatible partners (e.g., dead or different sized cells), and (iii) pair with other partners as a result of the hydrodynamic instabilities generated by collective cell sinking. This is, eminently, a cell abundance-dependent process, therefore being more effective when population sinking is synchronized. We suggest that this selective process, enabling matching of size-compatible healthy partners, could be fundamental in understanding sexual reproduction in pennate diatoms.

During summer, when oligotrophic conditions prevail offshore in the Mediterranean Sea, enhanced phytoplankton stripes are often observed in nearshore waters. In this study, we examine the cross-shore hydrographic variability and the associated microbial plankton communities in this zone. Detailed cross-shore underway sampling at 47 coastal sites spread along the Balearic and Catalan coasts revealed the widespread existence of narrow bands of warm and decreased salinity water beholding high phytoplankton biomass (up to 50-fold vs. offshore chlorophyll). Most intense physical and biological anomalies along these transects were generally constrained to the first hundred meters from the shoreline (i.e., a transition zone starting at similar to 400 m). We use Principal Component Analysis (PCA) and k-means cluster analysis to categorize temperature, salinity and chlorophyll (T, S and Chl) in three main types of cross-shore trends. Prevalence of exponential-shaped Chl trends was observed particularly in areas with shoreward directed winds (B1-type). The other two trends (B2 and B3) presented variations off the coast produced by alongshore structures like river plumes, city outfalls and other features. Exponential-shaped cross-shore chlorophyll distribution (B1-type) accumulated 90% of the total transect Chl variation in the first 367 +/- 190 m from the shoreline, whereas this distance was variable in the other profile types. Repeated daily sampling at one site with this transect typology revealed that wind forcing variations produced fast response on cross-shore T and S properties. Chl was less sensitive to changes at this time-scale. Phytoplankton communities exhibited site-dependent responses to the nearshore environment. Pico- and nanoplankton assemblages, typically dominating coastal assemblages during summer in the Mediterranean Sea, showed lower cross-shore variation. Conversely, larger response to nearshore conditions was observed in microplankton populations. These larger cells, represented by dinoflagellates, cryptophytes and diatoms, were able to actively exploit the nearshore conditions constituting an independent and distinct assemblage from that one prevailing offshore. Our results suggest that despite the importance of local-scale processes in determining biotic structure, some common patterns emerge providing clues on the main drivers of this nearshore niche.

XIII Reunion Iberica de Algas Toxicas y Biotoxinas Marinas (REDIBAL 2018) - XIII Reunion Iberica de Fitoplancton Toxico - XIII Iberian Toxic Algae and Marine Biotoxins Meeting, VI Simposio Internacional de Ciencias del Mar - VI International Symposium of Marine Sciences (ISMS 2018), 20- 22 June 2018, Vigo.-- 1 page

Changes in phytoplankton composition reveal relevant information about the response of aquatic systems to environmental drivers. Here, we propose the combined use of particle size measurements and pigment signatures to analyze the changes in the composition of phyto plankton communities at a coastal location. Canonical correlation analysis (CCA) was applied to separate phytoplankton signals from non-algal components of particulate matter in concurrent measurements of particle size distribution and pigment concentrations (chlorophylls a, b and c). Using this method, we were able to identify phytoplankton community structure variations at size and functional levels associated with the water column during the spring to summer transition at a Mediterranean coastal site. Some taxa with characteristic size spectrum signatures such as Pseudo-nitzschia sp., which produced an intense (up to 5 x 10(5) cells l(-1)), but ephemeral bloom, could also be identified. The general patterns of phytoplankton succession obtained using this methodology were corroborated by light microscopy and flow cytometry identification. Phytoplankton biovolume comparisons between both methods were highly consistent (r = 0.75, p < 0.01). We consider that combined pigment and size structure analysis using CCA is a useful tool to determine reorganization patterns of phytoplankton via changes in species composition.

The 18th International Conference on Harmful Algae (ICHA), From ecosystems to socio-ecosystems, 21-26 October 2018, Nantes, France.-- 1 page

Bysmatrum subsalsum is a cosmopolitan dinoflagellate species that inhabits marine and transitional habitats. Despite its wide distribution, information on the morphological variability, phylogeny and ecology of B. subsalsum is scarce. In this study, we provide morphological and molecular data on B. subsalsum strains and wild cells from different locations in the Mediterranean Basin. The dynamics of cell abundances and the associated environmental conditions during a field bloom are also described. Genetic sequences of B. subsalsum obtained in this study showed large intraspecific differences, clustering in two well‐differentiated clades. Despite a certain degree of variation with respect to cell size, apical pore complex (APC) morphology and size, and cingulum displacement, cells from the two clades showed similar morphological traits. These findings indicated the occurrence of cryptic species. Comparisons of the morphology of our B. subsalsum specimens with the few descriptions available in the literature revealed larger than previously known intraspecific morphological variability. Phylogenetic trees inferred from the concatenated SSU, 5.8S‐ITS, and LSU rRNA and the individual 5.8S‐ITS regions suggested the inclusion of Bysmatrum in the Peridiniales and a close phylogenetic relationship with Peridinium sensu stricto. However, the low statistical support prevented the assignment of Bysmatrum to a particular family of Peridiniales. Ecological data obtained from a bloom in La Pletera salt marshes (Catalan Coast, Spain) suggested the species reaches high cell abundances at water temperatures >20°C and salinity levels >30. Our results add new information regarding the morphology, phylogeny, and ecology of B. subsalsum.

Advection by ocean currents modifies phytoplankton size structure at small scales (1–10 cm) by aggregating cells in different regions of the flow depending on their size. This effect is caused by the inertia of the cells relative to the displaced fluid. It is considered that, at larger scales (greater than or equal to 1 km), biological processes regulate the heterogeneity in size structure. Here, we provide observational evidence of heterogeneity in phytoplankton size structure driven by ocean currents at relatively large scales (1–10 km). Our results reveal changes in the phytoplankton size distribution associated with the coastal circulation patterns. A numerical model that incorporates the inertial properties of phytoplankton confirms the role of advection on the distribution of phytoplankton according to their size except in areas with enhanced nutrient inputs where phytoplankton dynamics is ruled by other processes. The observed preferential concentration mechanism has important ecological consequences that range from the phytoplankton level to the whole ecosystem.

Sampedro, Nagore ... et. al.-- 17th International Conference on Harmful Algae (ICHA), 9-14 October 2016, Florianopolis, Santa Catarina, Brazil.-- 1 page

We analyzed dissolved nutrient, trace metal and vitamin (B-vitamins and methionine) concentrations in the lower course of the Moulouya River (MR, Morocco) and its estuary. The flow of this African river has changed drastically (a reduction of almost 50%) in the last 50 years due to the regulation of the river flow through dams and alterations of the course constructed to satisfy population necessities and growing agricultural requirements. Consequently, it has produced a remarkable increase in nitrate concentrations (up to 270 mu M) and alteration of N:P ratios within the river, as well as a reduction of overall P and Si efflux to nearby coastal waters. Despite the historical mining activities in the upper MR, concentrations of Pb, Zn and other metals in sediments and waters do not display significant contamination as compared with other Mediterranean rivers, mainly due to the retention by dams of upstream metal contamination. Mean concentrations of dissolved B-vitamins in the river showed lower levels (13-55% lower) than those in coastal waters and hence the river does not represent an important B-vitamin source. (C) 2016 Elsevier Ltd. All rights reserved.

We investigated the species-specific phosphorus (P) nutrition sources in the microphytoplankton community in the Mahon estuary (Minorca, Western Mediterranean) in 2011, under two contrasting hydrographic scenarios. Estuarine flow, nutrient concentrations, phytoplankton community composition and enzyme-labeled fluorescence (ELF) were measured in June and October, corresponding to the beginning and the end of summer. Dissolved inorganic nitrogen (DIN) and inorganic phosphate (Pi) exhibited enhanced concentrations in the inner estuary where N:P molar ratios suggested P-limitation in both surveys. Pi was low and variable (0.09±0.02 μmol•l-1 in June and 0.06±0.02 μmol•l-1 in October), whereas organic phosphorus remained a more reliable P source. Even though ambient Pi concentrations were slightly higher on June, when the microphytoplankton assemblage was dominated by dinoflagellates, the percentage of cells expressing ELF labeling was notably higher (65% of total cells) than in October (12%), when the presence of diatoms characterized the microphytoplankton community. ELF was mainly expressed by dinoflagellate taxa, whereas diatoms only expressed significant AP in the inner estuary during the June survey. A P-addition bioassay in which response of AP to Pi enrichment was evaluated showed remarkable reduction in AP with increasing Pi. However, some dinoflagellate species maintained AP even when Pi was supplied in excess. We suggest that in the case of some dinoflagellate species AP is not as tightly controlled by ambient Pi as previously believed. AP activity in these species could indicate selective use of organic phosphorus, or slow metabolic response to changes in P forms, rather than physiological stress to low Pi availability. We emphasize the importance of identifying the links between the different P sources and the species-specific requirements, in order to understand the ecological response to anthropogenic biogeochemical perturbations.

The size structure of phytoplankton reveals relevant information on the structure and response of aquatic systems to environmental drivers. To estimate the phytoplankton size distribution, we combined simultaneous particle size measurements obtained with a laser in situ scattering and transmissometry instrument (LISST) and fluorescence profiles using canonical correlation analysis (CCA). We tested the performance of this method with a series of synthetic laboratory samples generated by mixing cultured phytoplankton cells and natural sediments with grain sizes within the size range of phytoplankton. Our results revealed that the method yields reliable estimation of the algal fraction allowing the discrimination of phytoplankton size distribution when algal cells constitute >25% of total suspended particulate matter. Uncertainties arise in very turbid waters and when samples are composed of two phytoplankton species with very different contribution to chlorophyll in terms of cell size. Application of the proposed method in a survey of 37 stations carried out in Palma Bay (Mediterranean Sea) effectively represented the patterns of four main size fractions dominating coastal phytoplankton biomass, demonstrating the utility of the method. Compared to previous published methods, the proposed method is more robust because it is not impeded by the presence of non-algal components.