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Recently, natural and anthropogenic pressures caused an apparent increase in the frequency and spread of red Noctiluca scintillans (RNS) blooms. Here, we describe this potential expansion and the associated environmental factors based on an extensive literature review (1857–2023). Our analysis suggests that Noctiluca increased over time in several Australian, Chinese and European coastal regions. We point to eutrophication, ocean warming and deoxygenation as possible drivers of these intensifications. Moreover, we demonstrate Noctiluca 's importance for coastal ecosystems: with competitive advantages causing fast and intense blooms, Noctiluca has the potential to alter plankton communities, influencing productivity in affected areas. Throughout our analysis, we identified major knowledge gaps that are relevant to assess Noctiluca : (i) challenges in determining its spatiotemporal evolution; (ii) limited knowledge about drivers triggering and ending blooms; (iii) scarce information about feeding, reproduction and interaction in situ and (iv) uncertainty regarding its contribution to carbon export. We hypothesize that these gaps are related to limitations in traditional sampling techniques, and we highlight the need for a holistic approach combining traditional with novel techniques like remote sensing and underwater cameras. Our suggested approach could help filling the identified gaps and facilitate predictions of bloom dynamics and impacts under future climate conditions. [ABSTRACT FROM AUTHOR]

Cyanobacteria are the most common toxigenic algae in inland waters. Their toxins can affect the health of aquatic and terrestrial organisms, including humans. Other algal groups, such as haptophytes (e.g., Prymnesium parvum) and euglenoids (e.g., Euglena sanguinea), can also form harmful algal blooms (HABs) whose toxins cause injury to aquatic biota but currently have no known effects on human health. Prymnesium parvum, however, is responsible for some of the worst HAB-related ecological disasters recorded in inland waters. Here, we provide an overview of the primary toxigenic algae found in U.S. inland waters: cyanobacteria (planktonic forms), P. parvum, and E. sanguinea with the objective of describing their similarities and differences in the areas of HAB ecology, algal toxins, and the potential for future range expansion of HABs. A detailed account of bloom habitats and their known associations with land cover and use is provided from the perspective of water quality. This review revealed that salinity may have an influence on inland cyanobacterial blooms and cyanotoxins that had not been fully recognized previously. [ABSTRACT FROM AUTHOR]

There is often considerable uncertainty in parameters in ecological models. This uncertainty can be incorporated into models by treating parameters as random variables with distributions, rather than fixed quantities. Recent advances in uncertainty quantification methods, such as polynomial chaos approaches, allow for the analysis of models with random parameters. We introduce these methods with a motivating case study of sea ice algal blooms in heterogeneous environments. We compare Monte Carlo methods with polynomial chaos techniques to help understand the dynamics of an algal bloom model with random parameters. Modelling key parameters in the algal bloom model as random variables changes the timing, intensity and overall productivity of the modelled bloom. The computational efficiency of polynomial chaos methods provides a promising avenue for the broader inclusion of parametric uncertainty in ecological models, leading to improved model predictions and synthesis between models and data. [ABSTRACT FROM AUTHOR]

Algal blooms represent a pivotal ecological phenomenon in marine ecosystems, exerting significant influence on energy transfer, material cycling, and ecological structure and function. The frequent occurrence of harmful algal blooms (HABs) directly jeopardizes ecosystem integrity, compromises food safety, and challenges the sustainability of food supply, thereby affecting socio-economic development and human well-being. In recent decades, technological advancements in in-situ monitoring and remote sensing have greatly improved our capacity to monitor the oceans, providing unparalleled opportunities for not only the detection of algal blooms but also their dynamic processes and mechanisms. However, monitoring programmes are not always capable of covering the temporal and spatial scale of algal blooms, especially in open water ecosystems. Therefore, it remains essential to utilize models for interpreting observational results. In this review, we evaluated recent studies on models of algal blooms, which can be categorized into three main types: conceptual models, empirical-statistical models (from simple machine learning models to state-of-the-art deep learning models), and mechanistic models (process-based models). We reviewed the development and refinement of representative cases for each model type and compared their applicability, strengths, and limitations. Subsequently, we summarized the applications of these models in exploring algal bloom dynamics, short-term forecasting (a few days to seasonal), and long-term predictions (interannual or longer). We also proposed several recommendations for how algal bloom modeling can move forward: 1) Integrate various automated monitoring platforms and remote sensing techniques to obtain more comprehensive data for model validation; 2) Develop more powerful deep learning models to fully exploit their immense potential in algal bloom prediction; and 3) Incorporate molecular ecology and omics technologies to enhance parameterization schemes for numerical models. [Display omitted] • This review assesses the progress and application of conceptual, empirical, and mechanistic models in algal blooms. • Conceptual models serve as simplified frameworks for understanding the formation and dynamics of algal blooms. • Machine learning and deep learning models significantly improve the accuracy and timeliness of algal bloom prediction. • Mechanistic models reveal a wide range of physical and ecological dynamics of algal blooms. [ABSTRACT FROM AUTHOR]

This study investigated the temporal and spatial variations of Takayama blooms in Uranouchi Inlet, Japan. From July to September 2017, Takayama cells appeared (≥1 cell mL-1) at depths of 0-10 m, temperatures of 25.4-31.7°C, and salinities of 23.1-34.2. The maximum cell density was 1.37-103 cells mL-1. By analyzing partial rDNA sequences of Takayama strains collected at the bloom initiation, we found Takayama acrotrocha/Takayama xiamenensis and Takayama tasmanica in the Uranouchi Inlet. This study contributes to understanding of the dynamics of and risk to aquaculture of Takayama blooms in the coastal waters of Japan. [ABSTRACT FROM AUTHOR]

For nearly a century, phytoplankton spring blooms have largely been explained in the context of abiotic factors regulating cellular division rates (e.g., mixed-layer light levels). However, the accumulation of new phytoplankton biomass represents a mismatch between phytoplankton division and mortality rates. The balance between division and loss, therefore, has important implications for marine food webs and biogeochemical cycles. A large fraction of phytoplankton mortality is due to the combination of microzooplankton grazing and viral lysis, however, broad scale simultaneous measurements of these mortality processes are scarce. We applied the modified dilution assay along a West-to-East diagonal transect in the North Atlantic during spring. Our results demonstrate positive accumulation rates with losses dominated by microzooplankton grazing. Considering the dynamic light environment phytoplankton experience in the mixed surface layer, particularly in the spring, we tested the potential for incubation light conditions to affect observed rates. Incubations acted as short-term ‘light’ perturbations experiments, in which deeply mixed communities are exposed to elevated light levels. These “light perturbations” increased phytoplankton division rates and resulted in proportional changes in phytoplankton biomass while having no significant effect on mortality rates. These results provide experimental evidence for the Disturbance-Recovery Hypothesis, supporting the tenet that biomass accumulation rates co-vary with the specific rate of change in division.

For nearly a century, phytoplankton spring blooms have largely been explained in the context of abiotic factors regulating cellular division rates (e.g., mixed-layer light levels). However, the accumulation of new phytoplankton biomass represents a mismatch between phytoplankton division and mortality rates. The balance between division and loss, therefore, has important implications for marine food webs and biogeochemical cycles. A large fraction of phytoplankton mortality is due to the combination of microzooplankton grazing and viral lysis, however, broad scale simultaneous measurements of these mortality processes are scarce. We applied the modified dilution assay along a West-to-East diagonal transect in the North Atlantic during spring. Our results demonstrate positive accumulation rates with losses dominated by microzooplankton grazing. Considering the dynamic light environment phytoplankton experience in the mixed surface layer, particularly in the spring, we tested the potential for incubation light conditions to affect observed rates. Incubations acted as short-term 'light' perturbations experiments, in which deeply mixed communities are exposed to elevated light levels. These "light perturbations" increased phytoplankton division rates and resulted in proportional changes in phytoplankton biomass while having no significant effect on mortality rates. These results provide experimental evidence for the Disturbance-Recovery Hypothesis, supporting the tenet that biomass accumulation rates co-vary with the specific rate of change in division. [ABSTRACT FROM AUTHOR]

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.

We employed a detection method to quantify Alexandrium catenella (Group I), one of the causative species for paralytic shellfish poisoning (PSP) in Jinhae-Masan Bay, Korea, targets sxtA4 , via chip-based digital PCR. Additionally, we explored the dynamics of Alexandrium during the spring of 2022 using an rDNA-based quantitative PCR (qPCR) assay to enhance the performance of the dPCR assay. In matching dPCR results with PSP monitoring reports, we optimized a cell regulatory threshold of 102 cells L−1, the maximum cell density when shellfish harvesting was permitted, for the dPCR assay. This threshold functioned similar to the PST threshold used in mouse bioassays (MBAs). Furthermore, we validated a total concordance rate of 83.8 % between the two assays for 2020–2022, reaching a maximum of 96.2 % in 2020. Thus, the result of dPCR could complement MBAs, facilitating the early detection of PSP outbreaks. • We optimized a cell regulatory threshold of 102 cells L−1. • We validated a total concordance rate of 83.8 % between dPCR assay and MBAs. • Thus, dPCR assay can complement MBAs. [ABSTRACT FROM AUTHOR]

The East Asian marginal seas are among the most productive fisheries grounds. However, in recent decades they experienced massive proliferations of jellyfish that pose vast challenges for the management of harvested fish stocks. In the Korean Peninsula, the common bloom-formers Scyphozoan species Aurelia coerulea and Nemopilema nomurai are of major concern due to their detrimental effects on coastal socio-ecological systems. Here, we used pluriannual field observations spanning over 14 years to test the extent of climate influence on the interannual variability and bloom dynamics of A. coerulea and N. nomurai. To depict climate-jellyfish interactions we assessed partitioning effects, direct/indirect links, and the relative importance of hydroclimate forces on the variability of these species. We show that jellyfish interannual patterns and bloom dynamics are shaped by forces playing out at disparate scales. While abundance changes and earlier blooms of A. coerulea were driven by local environmental conditions, N. nomurai interannual patterns and bloom dynamics were linked with regional climate processes. Our results provide a synoptic picture of cascading effects from large scale climate to jellyfish dynamics in the Korean Peninsula that may affect fisheries sustainability due to the prominent detrimental impact these species have in the region.

• A qPCR assay reliably quantified two genetically different Amoebophrya sp. 1 and sp. 2 infecting C. polykrikoides. • Two Amoebophrya parasites exhibited distinct dynamic patterns during the harmful blooms. • Amoebophrya sp. 2 had greater impact on the host C. polykrikoides population dynamics than Amoebophrya sp. 1. During the bloom events of the harmful dinoflagellate Cochlodinium polykrikoides in August and October, 2012, infections by two different Amoebophrya species were observed in Korean coastal waters. To investigate the dynamics of the two parasites and their relative impact on the host populations, a quantitative real-time PCR (qPCR) method was applied to detect and quantify the parasites in the free-living and parasitic stages. Each specific primer set of the target species, Amoebophrya sp. 1 and sp. 2 was designed on the large subunit (LSU) and the first internal transcribed spacer (ITS1) of ribosomal RNA (rRNA) gene, respectively. Dynamics of the two Amoebophrya species via qPCR assay showed distinct patterns during the C. polykrikoides bloom events. Amoebophrya sp. 1 showed peaks during both bloom events in August and October with relatively low copies (106 to 107 copies L−1), while Amoebophrya sp. 2 appeared only during the bloom event in October with very high copies (109 to 1010 copies L−1). Overall, the qPCR measurements for the dynamics of two Amoebophrya species in the parasitic stage (> 5 μm fractions) were consistent with parasite prevalence through microscopic observations. Amoebophrya sp. 1 infections were observed during both bloom events in August and October with relatively low parasite prevalence (0.1–1.5%), while Amoebophrya sp. 2 infections were detected only during the bloom event in October with high prevalence (up to 45%). Taken together, Amoebophrya sp. 1 may be a generalist and C. polykrikoides may not be its primary host, while Amoebophrya sp. 2 may be a specialist which can substantially impact host population dynamics. [ABSTRACT FROM AUTHOR]

Highlights • Ecology and proliferation dynamics of O. cf. ovata are driven by complex interactions. • Higher abundances of O. cf. ovata observed in sheltered zones. • The dominant macroalgal community has a significant effect on bloom dynamics. • Urbanised sites are more prone to the proliferation of toxic benthic microalgae. • Larger risk exposure to toxic effects for humans in urban and sheltered areas. Abstract In the last few decades, Ostreopsis spp., toxic benthic dinolagellates of tropical origin, generated large interest in the Mediterranean Sea, where several bloom events have been observed. Ecology and proliferation dynamics of O. cf. ovata are driven by complex interactions among biotic and abiotic drivers, and understanding mechanisms triggering bloom events is still far from being complete. The aim of the present study is to highlight the role of different habitat conditions, elucidating the effects of i) exposure to hydrodynamic conditions, ii) macroalgal community and iii) urbanisation level, in driving O. cf. ovata bloom dynamics. A significant effect of hydrodynamics was observed only for cells in seawater, with higher abundances in sheltered zones, irrespective of the urbanisation level. Similarly, a significant effect of the dominant macroalgal community, with higher abundances in Corallinales and turf dominated communities, and lower ones in Cystoseira amentacea canopies, has been recorded, consistently in the differently urbanised sites. Additionally, stretches of the coast suffering from a more intense anthropic exploitation are in general more prone to the proliferation of potentially toxic benthic microalgae. All these results imply a larger risk exposure to toxic effects for humans in urban beaches and sheltered areas, usually more attended by swimmers and bathers. These findings underline the need to preserve, and eventually restore, canopy dominated assemblages, which presently are under regression because of human threats, providing a straightforward example that restoration of relevant habitats implies a cascading improvement of human welfare. [ABSTRACT FROM AUTHOR]

The aim of the present study was to assess the frequency of viral infections in colony-embedded cells of the cyanobacteria Aphanizomenon flos-aquae and Microcystis aeruginosa collected from the brackish Curonian Lagoon. Natural and mitomycin C-treated A. flos-aquae and M. aeruginosa samples were examined for the presence of viruses and lysis by a combination of light-, epifluorescence and transmission electron microscopy techniques. Here we report a lack of evidence for virus infection, progeny formation and cell lysis in colony-embedded cells of A. flos-aquae and M. aeruginosa. These results indicated that viruses contribute little to the mortality of these cyanobacteria when the latter occur in colonies. Consequently, the results supported the hypothesis that colony formation can, at least temporarily, provide an efficient strategy for protection against virus-induced mortality. Finally, assuming that grazing has a negligible effect on colony-embedded cells in the Curonian Lagoon, we propose that most of the cyanobacterial biomass produced is lost from the pelagic food web by sedimentation.

One of the most dramatic large-scale features in the ocean is the seasonal greening of the North Atlantic in spring and summer due to the accumulation of phytoplankton biomass in the surface layer. In 1953, Harald Ulrik Sverdrup hypothesized a now canonical mechanism for the development and timing of phytoplankton blooms in the North Atlantic. Over the next 60 years, Sverdrup's Critical Depth Hypothesis spurred progress in understanding of bloom dynamics and offered a valuable theoretical framework on which to build. In reviewing 60 years of literature, the authors trace the development of modern bloom initiation hypotheses, highlighting three case studies that illuminate the complexity, including both catalysts and impediments, of scientific progress in the wake of Sverdrup's hypothesis. Most notably, these cases demonstrate that the evolution of our understanding of phytoplankton blooms was paced by access not only to technology but also to concurrent insights from several disciplines. This exploration of the trajectories and successes in bloom studies highlights the need for expanding interdisciplinary collaborations to address the complexity of phytoplankton bloom dynamics.

The population dynamics of different Pseudo-nitzschia species, along with particulate domoic acid (pDA) concentrations, were studied from May 2012 to December 2013 in the Bay of Seine (English Channel, Normandy). While Pseudo-nitzschia spp. blooms occurred during the two years of study, Pseudo-nitzschia species diversity and particulate domoic acid concentrations varied greatly. In 2012, three different species were identified during the spring bloom ( P. australis , P. pungens and P. fraudulenta ) with high pDA concentrations (∼1400 ng l −1 ) resulting in shellfish harvesting closures. In contrast, the 2013 spring was characterised by a P. delicatissima bloom without any toxic event. Above all, the results show that high pDA concentrations coincided with the presence of P. australis and with potential silicate limitation (Si:N < 1), while nitrate concentrations were still replete. The contrasting environmental conditions between 2012 and 2013 highlight different environmental controls that might favour the development of either P. delicatissima or P. australis . This study points to the key role of Pseudo-nitzschia diversity and cellular toxicity in the control of particulate domoic acid variations and highlights the fact that diversity and toxicity are influenced by nutrients, especially nutrient ratios. [ABSTRACT FROM AUTHOR]

The spatial and temporal variations in the composition of Pseudo-nitzschia during bloom events from August 2005 to February 2006 were characterised in two bays of the NW Mediterranean Sea (Alfacs and Fangar Bay) by means of scanning electron microscopy (SEM). The study provides detailed records of the Pseudo-nitzschia community at the species level and describes its relationship with both the surrounding environmental conditions and biotic factors such as the accompanying phytoplankton community. The size distributions of several species of Pseudo-nitzschia were monitored during the bloom events. These measurements may serve as indicators of the physiological status of the cells. The species observed in the two bays were Pseudo-nitzschia calliantha, P. delicatissima, P. fraudulenta, P. multistriata, and P. pungens. In Alfacs Bay, a mixed species bloom of P. calliantha and P. delicatissima began in late August 2005 and lasted 11 weeks. In Fangar Bay, the Pseudo-nitzschia bloom was limited to the period from early August to late September 2005 and comprised P. calliantha and P. delicatissima. Commonly, the proliferation of Pseudo-nitzschia was mono-specific or was accompanied by other diatoms. Two objectively defined groups were identified by the statistical analysis in Alfacs bay; the first was made up only of winter samples and the second of summer and autumn samples. The first group was defined by a high concentration of NO3¯ and low concentrations of NH4+, conditions associated with a high abundance of P. delicatissima and a low abundance of P. calliantha. The second group expressed the opposite characteristics. A succession of different blooming species of Pseudo-nitzschia lasting months in Alfacs Bay is described.

The study was based on CTD-casts performed on 5 consecutive daysat 7 positions along a shallow- to deep-water transect duringthe spring bloom in the southwest Kattegat. The development,dynamics and fate of the sub-surface chlorophyll maximum (SCM)are described. The SCM developed at a constant rate of1.4 mg chl a m-3 d-1,which is equal to a carbon fixation rate of49.0 mg C m-3 d-1. The SCM developed at 6 m depth at low irradiancelevels (10-43.0 µE m-2 s-1). Chl a concentrations reachedup to 23 mg chl a m-3 in the centre of the SCM. Growth ratesin the SCM were estimated at 0.82 d-1. The water column wasonly weakly stratified, with nutrients in excess in the wholeof the water column. The SCM was relocated vertically to depthsbelow the photic zone by wind-induced advection between the bayand the outer Kattegat. There were indications of a horizontalrelocation of the SCM by an internal standing wave. Applicationof high spatial and temporal resolution made it possible to estimatekey SCM parameters, such as growth rates [mg chl a m-3 d-1]and carbon fixation rate [mg C m-3 d-1],on the basis of chl a variations in time and space.

Several species of the genus Karenia (Dinophyceae) form blooms and often cause the mortality of cultured and wild fish. In Japan, blooms caused by two species – namely Karenia mikimotoi and Karenia brevis – have been reported so far. On the basis of morphological and molecular-phylogenic examinations, the present investigation found Karenia papilionacea and its novel sister phylotype for the first time in the coastal waters of the various regions of Japan. Of 34 strains isolated from the coastal waters, 27 strains displayed the typical morphological characteristics of K. papilionacea and further showed consensus DNA sequences corresponding to those of the originally described K . papilionacea . The other 7 strains displayed the same morphological characteristics of K. papilionacea , but showed divergent DNA sequences, at a genetic distance of over 0.04 (Internal Transcribed Spacer regions) from those of the original phylotype of K . papilionacea . These divergent strains were characterized as a novel sister phylotype (phylotype-I) of K . papilionacea . In the coastal waters of Japan, K . papilionacea -like ( K . papilionacea and/or its phylotype-I) formed blooms at 20.3–30.4 °C and salinity 30.1–33.9. No K . brevis was identified in Japanese coastal waters during this study. These findings demonstrated that K . papilionacea occurs along the coasts of western Japan and possibly shares several coastal regions with K . mikimotoi and K . papilionacea phylotype-I. In order to assess the risks of Karenia blooms to aquaculture, it is essential that the growth physiology and ichthyotoxicity of K . papilionacea and its novel phylotype should be characterized. [ABSTRACT FROM AUTHOR]

The microlage Dunaliella salina, a major producer in salterns, is a serious problem for salt production. In this study we tried to assess if Fabrea salina can control D. salina. By parameterising numerical and functional response (growth and grazing vs prey abundance, respectively) at 90 psu and 30°C, where the ciliate is abundant and grows well, we developed a predator-prey model. The model is used to explore how change in microalga growth rate affect the dynamics, and the functional response is used in combination with field data to assess the potential impact of F. salina on D. salina. Over the 20 d simulation the ciliate controlled the prey population under all prey growth rates; although once D. salina were exhausted below the threshold level, F. salina died due to starvation, allowing the alga to increase in abundance, resulting in one or two predatorprey cycle, depending on prey growth rate. In general, the model predicted trends observed by others in the field, suggesting that it provided a good prediction of what may occur under the conditions we examined. Likewise we show that the ciliate can have a high impact on microalgal populations in the field. Finally, a literature review indicated that F. salina could be a good competitor with other protozoa and metazoan in salterns, depending on salinity and temperature, which requires further study and attention. In summary, we encourage continued studies on this unique ciliate on solar salterns and suggest that it may be useful in the bio-control of micoalgae. [ABSTRACT FROM AUTHOR]

Studies of annual successions and inter-annual variations in sub-Arctic and Arctic microplankton assemblages are required in order to understand the structure and function of marine ecosystems. This study depicts the microplankton (>20 μm) structure in a sub-Arctic tidewater glacial fjord system, SW Greenland. The descriptions are based on monthly net hauls collected between January 2006 and December 2010. Two blooms, with distinctive species compositions, were identified across all years: a spring bloom and a summer/autumn bloom. In addition, the winter season-with weak stratification, deep tidal mixing, and dense coastal inflows-was characterised by a separate species composition at much lower abundance. Here, the highest variety of microplankton groups was recorded and represented by diatoms ( Chaetoceros spp. and Thalassiosira spp.), silicoflagellates, dinoflagellates, and ciliates. During the spring bloom, species correlated with higher light intensities, i.e. haptophytes and diatoms ( Thalassiosira spp. and Fragilariopsis spp.), dominated the microplankton assemblage. Among these, diatoms were also correlated with cooler and fresher waters influenced by springtime melt. During the summer/autumn bloom, the microplankton assemblage was mainly represented by diatoms, such as Chaetoceros spp. 'Low-saline' chrysophytes were also present. The latter bloom coincides with elevated temperatures in the fjord and renewal of nutrients due to the onset of glacial meltwater run-off from the Greenland Ice Sheet. Our study shows a yearly recurrent succession of microplankton assemblages and that the annual succession is controlled primarily by ocean-fjord-glacier interactions. [ABSTRACT FROM AUTHOR]

Despite the global oceanic distribution and recognised biogeochemical impact of coccolithoviruses (EhV), their diversity remains poorly understood. Here we employed a metagenomic approach to study the occurrence and progression of natural EhV community genomic variability. Analysis of EhV metagenomes from the early and late stages of an induced bloom led to three main discoveries. First, we observed resilient and specific genomic signatures in the EhV community associated with the Norwegian coast, which reinforce the existence of limitations to the capacity of dispersal and genomic exchange among EhV populations. Second, we identified a hyper-variable region (approximately 21 kbp long) in the coccolithovirus genome. Third, we observed a clear trend for EhV relative amino-acid diversity to reduce from early to late stages of the bloom. This study validated two new methodological combinations, and proved very useful in the discovery of new genomic features associated with coccolithovirus natural communities. [ABSTRACT FROM AUTHOR]

Organisms with sexual and asexual reproductive systems benefit from both types of reproduction. Sexual recombination generates new combinations of alleles, whereas clonality favours the spread of the fittest genotype through the entire population. Therefore, the rate of sexual vs. clonal reproduction has a major influence on the demography and genetic structure of natural populations. We addressed the effect of reproductive system on populations of the dinoflagellate Alexandrium minutum. More specifically, we monitored the spatiotemporal genetic diversity during and between bloom events in two estuaries separated by 150 km for two consecutive years. An analysis of population genetic patterns using microsatellite markers revealed surprisingly high genotypic and genetic diversity. Moreover, there was significant spatial and temporal genetic differentiation during and between bloom events. Our results demonstrate that (i) interannual genetic differentiation can be very high, (ii) estuaries are partially isolated during bloom events and (iii) genetic diversity can change rapidly during a bloom event. This rapid genetic change may reflect selective effects that are nevertheless not strong enough to reduce allelic diversity. Thus, sexual reproduction and/or migration may regularly erase any genetic structure produced within estuaries during a bloom event. [ABSTRACT FROM AUTHOR]

• Cyanophycin synthesis-degradation genes were found in 21 of 23 Raphidiopsis strains. • N fluctuation was the factor triggerring cyanophycin accumulation in R. raciborskii. • Proposed a N threshold determining the N substrate used for cyanophycin synthesis. • The first attempt to elucidate the role of stored N in cyanobacterial dominance. Nutrient storage is considered a critical strategy for algal species to adapt to a fluctuating nutrient supply. Luxury phosphorus (P) uptake into storage of polyphosphate extends the duration of cyanobacterial dominance and their blooms under P deficiency. However, it is unclear whether nitrogen (N) storage in the form of cyanophycin supports persistent cyanobacterial dominance or blooms in the tropics where N deficiency commonly occurs in summer. In this study, we examined genes for cyanophycin synthesis and degradation in Raphidiopsis raciborskii , a widespread and dominant cyanobacterium in tropical waters; and detected the cyanophycin accumulation under fluctuating N concentrations and its ecological role in the population dynamics of the species. The genes for cyanophycin synthesis (cphA) and degradation (cphB) were highly conserved in 21 out of 23 Raphidiopsis strains. This suggested that the synthesis and degradation of cyanophycin are evolutionarily conserved to support the proliferation of R. raciborskii in N-fluctuating and/or deficient conditions. Isotope 15N-NaNO 3 labeling experiments showed that R. raciborskii QDH7 always commenced to synthesize and accumulate cyanophycin under fluctuating N conditions, regardless of whether exogenous N was deficient. When the NO 3 −-N concentration exceeded 1.2 mg L−1, R. raciborskii synthesized cyanophycin primarily through uptake of 15N-NaNO 3. However, when the NO 3 −-N concentration was below 1.0 mg L−1, cyanophycin-based N was derived from unlabeled N 2 , as evidenced by increased dinitrogenase activity. Cells grown under NO 3 −- N < 1.0 mg L−1 had lower cyanophycin accumulation rates than cells grown under NO 3 −- N > 1.2 mg L−1. Our field investigation in a large tropical reservoir underscored the association between cyanophycin content and the population dynamics of R. raciborskii. The cyanophycin content was high in N-sufficient (NO 3 −- N > 0.45 mg L−1) periods, and decreased in N-deficient summer. In summer, R. raciborskii sustained a relatively high biomass and produced few heterocysts (< 1%). These findings indicated that cyanophycin-released N, rather than fixed N, supported persistent R. raciborskii blooms in N-deficient seasons. Our study suggests that the highly adaptive strategy in a N 2 -fixing cyanobacterial species makes mitigating its bloom more difficult than previously assumed. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights: [•] Vegetative cell and cyst dynamics of the harmful algae species Alexandrium minutum in Cork Harbor, Ireland from 2004–2012. [•] Low density blooms (<100,000cellsL−1) allow persistence of bloom over decadal timescales. [•] Bloom magnitude is independent of the cyst density measured the previous winter. [•] A mean 2% encystment rate was recorded in the field regardless of the cell density. [Copyright &y& Elsevier]

We examined the environmental and biological factors related to blooms of the toxic dinoflagellate Pyrodinium bahamense in three shallow, restricted subtropical lagoons in the Gulf of California during the rainy summer. In the San José, Yavaros, and El Colorado lagoons, the vegetative stage peaked at 63, 108, and 151 (×103 cells l-1), respectively. At San José, production of cysts peaked at 9.7×103 g-1 of dry sediment mass as the bloom declined. Large diatoms predominated, with P. bahamense the most common dinoflagellate during the blooms. Abundance of P. bahamense at San José was positively correlated with salinity (r=0.50, p=0.0003), seawater temperature (r=0.44, p=0.005), silicates (r=0.45, p=0.003), and ammonium (r=0.32, p=0.005), and negatively correlated with dissolved oxygen (r=-0.34, p<0.0001). No such correlations were found at El Colorado and Yavaros. The environmental window that favors development of blooms is restricted to the summer and is influenced by seawater temperature, salinity, and relative concentrations of ammonium and phosphates that, in turn, depend on rainfall and runoff, which is greater on the eastern side of the Gulf where seawater quality is degraded. [ABSTRACT FROM AUTHOR]

Abstract: Life-cycle transitions play a key role in the bloom dynamics of many dinoflagellates. In this study, in situ excystment and encystment were monitored during recurrent Alexandrium minutum blooms in Arenys de Mar harbor (NW Mediterranean Sea) from October 2005 to May 2008. In addition, the dynamics of vegetative cells in the water column and resting cysts in the sediments were assessed. Excystment occurred continuously during the period studied. The excystment fluxes and the estimated excystment percentages indicated a pattern of alternating reduced and active excystment periods. From July to November, excystment percentages were <0.1%, whereas from December to June the A. minutum population underwent active excystment, with excystment percentages of 0.3–45.7%. Periods of active excystment coincided with increases in irradiance and water temperature, conditions also favorable for bloom development. During vegetative cell blooms, resting cyst formation coincided with periods marked by vegetative cell abundances in the water column of >2×103 cellsl−1. Resting cyst fluxes were higher when the abundance of vegetative cells in the overlying water column was greater. The excystment and encystment processes overlapped for 2 months during the extended blooms, indicating that newly formed resting cysts had overcome the mandatory dormancy period and were capable of germinating within the same bloom in which they were produced. Resting cysts in the surface sediment were rapidly depleted during periods of active excystment, but their production, although involving only a small fraction of the vegetative population, more than compensated for their loss. These results are discussed with respect to the role of frequent life-stage switches in determining the population dynamics and the maintenance of A. minutum blooms. [Copyright &y& Elsevier]

Abstract: In the past years, some coastal areas in the central and northern Baltic Sea have experienced recurrent blooms of the potentially toxic dinoflagellate Alexandrium ostenfeldii. The population dynamics and spatial distribution of the species were studied in the Föglö archipelago, a bloom area in Åland, northern Baltic Sea. During a two-year survey, cell and toxin concentrations of A. ostenfeldii were recorded in summer phytoplankton communities and related to environmental parameters. The studies revealed that A. ostenfeldii blooms were restricted to a small area in a narrow sound, where cells of this species were detected from May to September in 2009 and 2010. A. ostenfeldii proliferated to bloom concentrations (1.7–2.1×105 cellsL−1) only at water temperatures around 20°C during warm periods in July and August. Abundance of A. ostenfeldii did not significantly correlate with dissolved inorganic nutrient concentrations (p =0.4–0.6) but was related to high concentrations of resting cysts in the sediment (p <0.001). The blooms were not monospecific but A. ostenfeldii was a part of a diverse productive phytoplankton community forming 30–60% of the total biomass during the abundance peaks. This study provides the first evidence of paralytic shellfish poisoning (PSP) toxins produced by dinoflagellate blooms in the Baltic Sea: PSP toxin dynamics correlated with the progression of the A. ostenfeldii bloom with toxin peaks mirroring the species abundance peaks. No other potentially toxic species were identified from the phytoplankton community. PSP toxin concentrations of up to 2.3μgL−1 measured in the A. ostenfeldii cell fraction suggest that blooms may have toxic effects on co-occurring biota. [Copyright &y& Elsevier]

Abstract: An unarmored dinoflagellate bloom of Cochlodinium geminatum (Schütt) Schütt has been identified in the Pearl River Estuary, South China Sea during the severe dry season, from late October to early November, 2009, when temperature and salinity ranged between 20.0–27.2°C and 10.6–33.4, respectively. Light and scanning electron microscopy were used to identify the characteristics of C. geminatum and provided the clear morphological structure for this species. The organism was primarily found in chains of two cells or single cell, and no longer chains were observed. Cells were irregularly spherical or slightly dorso-ventrally, with size ranged between 28 and 36μm and longer than wide. A large nucleus in the center with numerous golden chloroplasts was present, and the cingulum made 1.5 turns around the cell. The concentration of C. geminatum ranged from 102 to greater than 107 cellsl−1 during the bloom period. Nutrient concentration ranges during the bloom were 1.29–81.00μM NO3, 0.14–12.14μM NO2, 0.21–6.29μM NH4, 0.23–6.26μM PO4 and 3.29–171.43μM SiO3, respectively. Total biomass expressed in terms of chlorophyll a ranged from 2.44 to 135.45μgl−1, with an average 19.9μgl−1 in surface water throughout the PRE. Two main clusters corresponding to the water sectors were defined with multivariate analysis (cluster and nMDS). Based on the composition and abundance of phytoplankton, spatial variations were observed at a significant level (ANOSIM, R =0.44, P <0.01). Although the pairwise correlation analysis detected no significant effect of any single environmental variable on the abundance of C. geminatum, the multivariate analysis (BIO-ENV) between biotic and abiotic variables resulted in the best variables combination with all measured factors involved (temperature, salinity, turbidity, NO3, NO2, NH4, PO4 and SiO3) which showed a combined effect during the bloom of C. geminatum in the Pearl River Estuary (ρ w =0.477). [Copyright &y& Elsevier]

Abstract: Paralytic Shellfish Poisoning (PSP) toxins are annually recurrent along the Massachusetts coastline (USA), which includes many small embayments and salt ponds. Among these is the Nauset Marsh System (NMS), which has a long history of PSP toxicity. Little is known, however, about the bloom dynamics of the causative organism Alexandrium fundyense within that economically and socially important system. The overall goal of this work was to characterize the distribution and dynamics of A. fundyense blooms within the NMS and adjacent coastal waters by documenting the distribution and abundance of resting cysts and vegetative cells. Cysts were found predominantly in three drowned kettle holes or salt ponds at the distal ends of the NMS – Salt Pond, Mill Pond, and Town Cove. The central region of the NMS had a much lower concentration of cysts. Two types of A. fundyense blooms were observed. One originated entirely within the estuary, seeded by cysts in the three seedbeds. These blooms developed independently of each other and of the A. fundyense population observed in adjacent coastal waters outside the NMS. The temporal development of the blooms was different in the three salt ponds, with initiation differing by as much as 30 days. These differences do not appear to reflect the initial cyst abundances in these locations, and may simply result from higher cell retention and higher nutrient concentrations in Mill Pond, the first site to bloom. Germination of cysts accounted for a small percentage of the peak cell densities in the ponds, so population size was influenced more by the factors affecting growth than by cyst abundance. Subsurface cell aggregation (surface avoidance) limited advection of the vegetative A. fundyense cells out of the salt ponds through the shallow inlet channels. Thus, the upper reaches of the NMS are at the greatest risk for PSP since the highest cyst abundances and cell concentrations were found there. After these localized blooms in the salt ponds peaked and declined, a second, late season bloom occurred within the central portions of the NMS. The timing of this second bloom relative to those within the salt ponds and the coastal circulation patterns at that time strongly suggest that those cells originated from a regional A. fundyense bloom in the Gulf of Maine, delivered to the central marsh from coastal waters outside the NMS through Nauset Inlet. These results will guide policy decisions about water quality as well as shellfish monitoring and utilization within the NMS and highlight the potential for “surgical” closures of shellfish during PSP events, leaving some areas open for harvesting while others are closed. [Copyright &y& Elsevier]

1. This study introduces delayed fluorescence (DF) excitation spectroscopy as an on-line tool for in situ monitoring of the composition and biomass of various colour classes of phytoplankton when they are photosynthetically active (cyanobacteria, chlorophytes, chromophytes and cryptophytes). The DF data are validated by comparison with those from conventional methods (weekly microscopic counts and the measurement of chlorophyll concentration). 2. The composition of phytoplankton as assessed by DF agreed reasonably well with the results from microscopic counts, particularly when differences in chlorophyll-specific DF integrals of the various colour classes were taken into account. 3. Integrals of DF spectra were converted into concentration of chlorophyll a using empirical factors derived from field data. The value of the conversion factor was nearly twice as high when the relative abundance of cyanobacteria was low (<15%) than when it was high. The converted DF-chl time series agreed well with chlorophyll measurements particularly when blooms were developing. As the DF method is inherently free of the interference caused by pigment degradation products, the discrepancy between the two data sets increased during the collapse of blooms and when sediment resuspension was intense. 4. Fourier spectrum analysis of the time series of DF-chl indicated that samples must be taken, at a minimum, every 2–3 days to capture the dynamics of phytoplankton. As a consequence, the dynamics of various algal blooms, including their timing, duration and net growth rate, could be estimated with greater confidence than by using conventional methods alone. 5. On-line DF spectroscopy is an advanced technique for monitoring daily the biomass and composition of the photosynthetically active phytoplankton in aquatic environments, including turbid shallow lakes. At present, the detection limit is around 1 mg DF-chl a m−3 in terms of total biomass but confidence in estimates of phytoplankton composition declines sharply below about 5 mg chl a m−3. 6. On-line DF spectroscopy represents a promising approach for monitoring phytoplankton. It will be useful in water management where it can act as an early-warning system of declines in water quality. In basic ecological research it can supplement manual methods. While default calibration spectra may be acceptable for routine monitoring, we suggest a careful individual calibration of the DF spectrometer for basic research. The statistical methods developed here help to assess the adequacy of various calibration sets. [ABSTRACT FROM AUTHOR]

The aim of this paper was to determine how the abundance of species of the flagellate genus Chrysochromulina (Haptophyta) varies in relation to environmental conditions and season in a coastal area of the Skagerrak in southern Norway. The study was based on a fourteen-year time series (1989–2002) comprising data on Chrysochromulina spp. abundance, temperature, salinity, and nutrient and chlorophyll-a concentrations. Environmental data were aggregated by depth and season, and Chrysochromulina abundance was expressed as annual average abundance, which was positively correlated to annual maximum abundance. The main seasonal occurrence of Chrysochromulina was between April and August, but the abundance displayed strong short-term (days) and inter-annual variation. Annual average abundance of Chrysochromulina species was positively and significantly correlated with spring and summer N:P (nitrate/phosphate) ratios, and negatively and significantly correlated with summer salinity and summer phosphate concentration. The analysis indicates that high and skewed spring N:P ratios, stratified conditions with a low salinity surface layer during summer together with low phosphate concentrations are associated with favourable conditions for Chrysochromulina. [Copyright &y& Elsevier]

The smallest known eukaryote, Ostreococcus tauri Courties et Chrétiennot-Dinet, was first reported as the dominant picoplankter in a French lagoon known for its diverse phytoplankton community and high oyster productivity. Long-term seasonal blooms of this picoeukaryote were observed in association with stable plankton communities. On 5 June 2001, a distinctive monotypic picoplankton bloom was detected by flow cytometry as part of an ongoing study of “brown tide” (Aureococcus anophagefferens ) bloom initiation in Long Island bays. The bloom reached a concentration of 5 × 10[sup 5] cells·mL[sup -1] in West Neck Bay and lasted less than 2 weeks. Epifluorescence microscopy and TEM indicated that the bloom organism was an Ostreococcus -like picoalga, the first ever observed in a Long Island bay. Many cells of this alga contained numerous virus-like particles. The Ostreococcus -like picoalga, which resembles O. tauri , was rare in samples collected the following week. Instead, a substantial increase in the Synechococcus population was observed. Such rapid population changes have not previously been reported for Ostreococcus . Viral lysis and grazing by heterotrophic nanoflagellates may have contributed to the rapid decline of the Ostreococcus -like cells in West Neck Bay. [ABSTRACT FROM AUTHOR]