Search Results (118)

Aquaculture is the fastest-growing food production sector, supplying more than half of the world’s seafood and projected to expand further to meet rising global protein demands. Among the various pressures confronting this industry, harmful algal blooms (HABs) rank among the most alarming. Ichthyotoxic flagellates are microalgae known for producing toxins or inducing gill damage that leads to widespread fish mortality. Their increasing frequency poses a critical threat to aquaculture, emphasizing the urgent need for effective and environmentally sustainable strategies to regulate and mitigate these harmful episodes. This study investigated the responses of three ichthyotoxic flagellates renowned for impacting aquaculture operations (Prymnesium parvum, Heterosigma akashiwo, and Fibrocapsa japonica) and tested their susceptibility to two routinely applied chemical agents, hydrogen peroxide (H₂O₂) and copper sulfate (CuSO₄). Mortality, viability, and motility were assessed alongside trajectory-based metrics, including mean squared displacement (MSD) and probability density function (PDF). The results revealed species-specific sensitivities: P. parvum was highly susceptible to H₂O₂, while H. akashiwo and F. japonica were more susceptible to copper toxicity. Ichthyotoxic flagellates exhibited differential sensitivities to chemical treatments, with copper sulfate generally achieving lower EC₅₀ thresholds and greater inhibition of motility than hydrogen peroxide, except in P. parvum. The rapid attenuation of motility at sublethal concentrations highlights swimming behavior as a functional vulnerability, reinforcing the potential for behavior-based mitigation strategies that minimize chemical loading and reduce unintended impacts on cultured fish and surrounding ecosystems. Full article

Achnanthidium catenatum exhibits both epiphytic and planktonic ecological types and forms multiple large-scale diatom blooms in different drinking water reservoirs. This study determined its growth and physiological characteristics under different nitrogen (N) or phosphorus (P) conditions. The study found that N ≤ 2.5 mg/L promoted its growth, while the promoting effect weakened at ≥5 mg/L. The lag phase of the growth cycle was shorter, taking only 6 days to reach peak density; meanwhile, it showed strong adaptability to P (0.5–3.5 mg/L), with peak density occurring by approximately 12 days. It was found that N-induced blooms formed earlier and lasted longer, whereas P-induced blooms were relatively delayed, more intense, and shorter in duration. Low and high concentrations of N, as well as P concentrations (≥0.1 mg/L), significantly promoted the formation of multicellular chain colonies (p < 0.05). The percentage of chain colonies was relatively higher during the lag phase and tended to exist as single cells during the stationary phase, at which time the colloidal extracellular polymeric substance (CEPS) content was higher and significantly correlated with changes in cell density. Alkaline phosphatase activity (APA) and malondialdehyde (MDA) content varied markedly under different N or P concentrations (p < 0.05). These results reveal the potential impact of N or P variations on the bloom-forming capacity of A. catenatum. Full article

This study investigates how environmental gradients shape the structure and interactions of coastal biotic assemblages in the Romanian Black Sea. A multi-trophic analysis was conducted across a network of stations in June 2023, integrating phytoplankton, microzooplankton, mesozooplankton, macrozooplankton, ichthyoplankton, and macrozoobenthos with key physico-chemical parameters. Principal component analysis revealed strong north–south contrasts: the northern sector was characterized by nutrient enrichment (nitrate, ammonium, and silicate) supporting phytoplankton blooms and microzooplankton peaks, while the southern sector showed more saline conditions and extended trophic coupling from phytoplankton through mesozooplankton to ichthyoplankton. The central sector appeared transitional, with community structure more closely related to oxygen and phosphate levels. In the north and south, plankton dynamics were strongly linked to nutrient availability, while macrozooplankton consistently aligned with salinity and silicate, reflecting their preference for more marine waters and partial decoupling from nutrient-driven pathways. Fuzzy Cognitive Map analysis indicated combined bottom-up and top-down control, with phytoplankton supporting mesozooplankton and macrozooplankton exerting strong negative pressure. Phytoplankton functioned as the main network driver, with mesozooplankton as the central mediator, and the persistent negative macrozooplankton effect suggests direct biological regulation beyond salinity influence. These findings highlight the dual structuring of Black Sea food webs and provide an integrative, multi-trophic baseline for ecosystem-based management and Marine Strategy Framework Directive Descriptor 4 (Food webs) implementation. Full article

Urban water bodies serve as biodiversity hot spots in a human-influenced landscape. We studied the backwater “Alte Donau” (Vienna, Austria), which has been the subject of ongoing management and restoration efforts. We aimed to capture short-term variations in the planktonic and benthic algal community during a vegetation period with a specific focus on Gloeotaenium loitlesbergerianum with its primary distribution in tropical regions. In total, 196 algal taxa were identified, indicating a high and balanced species diversity. Although the waterbody is shallow and densely colonized by macrophytes, phytoplankton and microphytobenthos exhibited significant differences in composition, particularly in spring. Less pronounced differences during summer were probably caused by macrophyte harvesting combined with recreational activities. We found a clear seasonal pattern with spring characterized by blooms of Ochrophyta, followed by a shift towards green algae, Dinophyta, and Cyanobacteria during summer and autumn. We found high variability in spring samples, whereas summer and autumn samples showed increasing similarity. Temperature, silicate, and alkalinity were the primary environmental factors structuring algal community composition. G. loitlesbergerianum was detected during warmer months from May through October across a temperature range of 14 to 28 °C, with highest abundances >20 °C. Warmer water and altered nutrient regimes not only stress native populations but also promote the establishment of new species such as G. loitlesbergerianum, accelerating community shifts. Therefore, sustained monitoring, targeted macrophyte restoration, and effective nutrient management are crucial for preserving both water quality and biodiversity in such systems. Full article

Research into the effects of environmental stressors associated with global climate change (GCC) on cyanobacteria and microalgae is scarce, with bloom-forming planktonic cyanobacteria being the exception. This study aimed to address the issue by assessing morphological and biochemical changes in cyanobacterial and microalgal cells exposed to an increased temperature (T), ultraviolet radiation (UVR) and carbon dioxide (CO₂) concentration. The strains selected were Calothrix sp. SLM0211 and Coelastrella sp. SLM0503, which were isolated from a coastal environment in the central Mediterranean island of Malta. Elevated UVR had a pronounced effect on Calothrix sp. filaments, which produced screening compounds and resorted to trichome coiling to enhance self-shading. Enhanced growth was observed in cultures of Calothrix sp. grown at an increased CO₂ concentration, which produced significantly high amounts of biomass, chlorophylls and carotenoids. An increased T resulted in stunted growth and low biomass accumulation in both strains. Each strain exhibited a unique response to T and UVR stressors, which stimulated the production of exopolymeric substances (EPS) and mycosporine-like amino acids (MAAs) in cultures of Calothrix sp. and lipid production in Coelastrella sp. cells. Our findings indicate that the effects of stressors related to GCC on cyanobacterial and microalgal cells are strain-specific, making changes at community and ecosystem levels difficult to predict. Full article

The impact of nitrogen on harmful algal blooms (HABs) and functions of biota in marine ecosystems under eutrophication is a topical issue of growing importance. The article aimed at describing the diversity of planktonic bloom-forming dinoflagellates in the SW Baltic Sea coastal waters under variable eutrophication. The analysis of 44 year-long database revealed 82 dinoflagellate species and demonstrated diversity patterns of ten common bloom-forming species, including seven mixotrophs from the genera Prorocentrum, Dinophysis, and Ceratium, under variable eutrophication evaluated using total nitrogen (TN) content in water. Based on the Intermediate Disturbance Hypothesis (IDH), we presumed those coastal waters with total nitrogen concentrations that are optimal to dinoflagellates to host greater taxonomic diversity compared to areas with non-optimum TN content. The results showed that the highest dinoflagellate species richness was associated with much lower TN concentrations than the optimum values for these species. Thus, our findings disagreed with the IDH. We suggested and discussed possible reasons of this inconsistency, including algal growth rates and disturbance frequency. We also updated the classification of eutrophication levels in the Baltic Sea based on the distribution of TN content and diversity of HAB-forming dinoflagellates. The results can contribute to predictive assessment of HABs under growing eutrophication. Full article

Cyanobacteria harmful algal blooms (CHABs) are most commonly caused by the proliferation of the toxic species, Microcystis aeruginosa. It is therefore of considerable interest to develop biological control processes which are economically feasible and scalable for this cyanobacteria that produces the cyanotoxin, microcystin. Some gastropods that are abundant in freshwater ecosystems can filter feed on floating planktonic microphytes. We investigated this in the freshwater snail, Sinotaia aeruginosa which indiscriminately accumulated M. aeruginosa, Chlorella vulgaris, and Trichormus variabilis (syn. Anabaena variabilis) The initial filtration rates were approx. 44 and 19 mL · g_wwt⁻¹ · h⁻¹ for unicellular and colony-forming M. aeruginosa, respectively. The pseudofaeces that were formed directly by filtration possessed a limited period of stability, and the bulk of the M. aeruginosa from pseudofaeces was eventually released back to the water column as undigested cyanobacteria. Nevertheless, the rate of sequestration of colonial M. aeruginosa into pseudofaeces was greater than its rate of release, thereby indicating that the temporary stability of pseudofaeces alone would be adequate to impede bloom formation. Therefore, these results provide evidence for using this gastropod in an effective preventative strategy for CHABs formation. Our results highlight the importance of understanding the impact of feeding mechanisms on ecosystem structure when proposing their use in biomanipulative processes aimed at correcting cyanobacteria impacted ecosystems. Full article

Accurately quantifying associated microbes is essential to understand the interactions between microplankton and their associated microbes. Most DNA-based methods, such as high-throughput sequencing, primarily assess the ratio of target objects to references in microplankton samples. However, simple random sampling (SRS) of individuals may lead to deviations in quantifying these ratios at the population level if these characteristics are associated with the reference content of individuals. This study considered group analysis, which involves detecting k groups with n individuals in each group, as an alternative approach and used simulated data based on the detection of Microcystis populations to evaluate the accuracy of different sampling plans. Our results indicate that increasing the number of individuals in each group could reduce sampling bias and improve the accuracy of comparisons between populations. Group analysis could also minimize the impact of the detection limit. This study demonstrated that, when detection methods only provide the ratio of target objects to references, group analysis is more appropriate than SRS for characterizing microplankton populations. Group analysis can be used not only for detecting associated microbes but also for identifying ingested organisms or the biochemical composition of microplankton. Our results also demonstrate how in situ individual-level studies support ecological investigations. Full article

Phytoplankton–mesozooplankton interactions play a central role in shaping Black Sea food web dynamics, yet their trophic coupling has been insufficiently investigated in policy-relevant frameworks. This systematic review of 86 peer-reviewed studies (1987–2025) synthesizes research trends, limitations, and knowledge gaps in the field. The analysis reveals a clear dominance of work on plankton community structure (81%), whereas topics such as modeling and scenario analysis (7%), ecosystem assessment (7%), and bloom dynamics and seasonality (5%) remain comparatively underrepresented. Post-2020 publications indicate a promising shift toward scenario-based frameworks, gelatinous zooplankton impacts, and trait-based indicators, although functional integration remains fragmented. Keyword co-occurrence and network analyses revealed a concentration on nutrient–phytoplankton–zooplankton pathways, while other themes—such as bioluminescence and redoxcline dynamics—appeared only marginally represented in the literature we analyzed. To support ecosystem-based management under the Marine Strategy Framework Directive (MSFD), we highlight three priorities: improving NPZD-type models, using trophic efficiency metrics, and standardizing plankton indicators across the region. Strengthening the mechanistic understanding of planktonic trophic linkages is critical for improving food web assessments and adaptive marine governance in the Black Sea. Full article

In this cross-disciplinary investigation, we uncover a suite of previously unexamined factors and their intricate interplay that hold causal relationships with the distribution of Trachurus japonicus in the northern reaches of the South China Sea, thereby extending the existing research paradigms. Leveraging advanced machine learning algorithms and causal inference, our robust experimental design uncovered nine key global and regional factors affecting the distribution of T. japonicus density. A robust experimental design identified nine key factors significantly influencing this density: mean sea-level pressure (msl-0, msl-4), surface pressure (sp-0, sp-4), Summit ozone concentration (Ozone_sum), F10.7 solar flux index (F10.7_index), nitrate concentration at 20 m depth (N3M20), sonar-detected effective vertical range beneath the surface (Height), and survey month (Month). Crucially, stable causal relationships were identified among Ozone_sum, F10.7_index, Height, and N3M20. Variations in Ozone_sum likely impact surface UV radiation levels, influencing plankton dynamics (a primary food source) and potentially larval/juvenile fish survival. The F10.7_index, reflecting solar activity, may affect geomagnetic fields, potentially influencing the migration and orientation behavior of T. japonicus. N3M20 directly modulates primary productivity by limiting phytoplankton growth, thereby shaping the availability and distribution of prey organisms throughout the food web. Height defines the vertical habitat range acoustically detectable, intrinsically linking directly to the vertical distribution and availability of the fish stock itself. Surface pressures (msl-0/sp-0) and their lagged effects (msl-4/sp-4) significantly influence sea surface temperature profiles, ocean currents, and stratification, all critical determinants of suitable habitats and prey aggregation. The strong influence of Month predominantly reflects seasonal changes in water temperature, reproductive cycles, and associated shifts in nutrient supply and plankton blooms. Rigorous robustness checks (Data Subset and Random Common Cause Refutation) confirmed the reliability and consistency of these causal findings. This elucidation of the distinct biological and physical pathways linking these diverse factors leading to T. japonicus density provides a significantly improved foundation for predicting distribution patterns globally and offers concrete scientific insights for sustainable fishery management strategies. Full article

Antipredator defenses of bloom-forming cyanobacteria species maximize their fitness but can reduce carbon and energy transfer efficiency to higher trophic levels, making them a key regulator of plankton communities in eutrophic waters. We investigated the grazing responses of the tropical cladoceran Moina micrura to different strains of the cyanobacteria Microcystis aeruginosa and Planktothrix isothrix, using a good food source (green algae Mono-raphidium capricornutum) as a control. Both Microcystis strains grow as unicellular and are microcystins producers; however, this cyanotoxin was not detected on the filamentous Planktothrix strains. M. micrura ingested all cyanobacteria at reduced rates compared to single diets with Monoraphidium. In mixed diets, food type had a significant effect on grazing responses, which differed interspecifically. Planktothrix was more grazed than Microcystis strains. Feeding selectivity on Monoraphidium was negatively affected by the increase of cyanobacteria in the diet. We observed varied responses across treatments, ranging from feeding inhibition to different degrees of tolerance toward cyanobacteria, particularly in non-microcystin-producing species. We also highlight the selectivity of small tropical cladocerans, a pattern that is not yet well documented. These findings emphasize that studies incorporating phyto- and zooplankton with a history of coexistence can provide more meaningful insights into natural ecosystem dynamics. Full article

Dinoflagellates are unicellular organisms that are crucial components of aquatic ecosystems, known as important primary producers and causes of harmful blooms. They have complex life cycles, including immotile stages, which contribute to their distribution and survival in unfavorable conditions. Temperature changes, primarily cold stress, significantly impact dinoflagellate physiology, influencing metabolic processes, growth rates, and encystment/excystment cycles. This study investigates the transcriptome of temporary cold-induced cysts in the marine planktonic dinoflagellate Prorocentrum cordatum. We compared gene expression in cysts subjected to a 7-h cold incubation with those returned to standard cultivation conditions and motile vegetative cells. Our results showed a marked predominance of downregulated genes in cold-induced cysts. Encystment affected signaling pathways, including calcium and protein kinase signaling, as well as RNA and protein metabolism. Upon returning to standard conditions, RNA metabolism was reactivated; upregulation of genes encoding some calcium-binding proteins and kinases was observed. Additionally, we analyzed RNA-binding pentatricopeptide repeat-containing proteins, the genes encoding which changed their expression in P. cordatum cysts, for similarities to plant MRL1 proteins. Finally, we focused on MEI2-like proteins to confirm their role in non-sexual cyst formation and position them within the diversity of MEI2 homologs in dinoflagellates. Full article

Kuibyshev Reservoir, the largest in the Volga basin, is poorly covered by modern molecular studies. The results of a metabarcoding study of pro- and eukaryotic microbial plankton in its lower section during the summer period are presented. Bacterioplankton composition was typical for most temperate freshwater bodies and characterized by the dominance of cyanobacteria, Pseudomonadota, Bacteroidota, Actinomycetota, and PVC superphylum (Verrucomicrobiota and Planctomycetota), with a somewhat increased proportion of the latter. The protist community was dominated by Cryptista, principally phototrophic, and various ciliates. Several picoeukaryotic groups were newly detected in the reservoir. A relationship between the composition of both bacterioplankton and protist communities and the stage of phytoplankton succession, including the cyanobacterial bloom, was observed. Some inconsistency between the cyanobacterial bloom phase and the structure of other parts of the microbial plankton is obviously due to some temporal delay, spatial station position, and inflow from tributaries. Heterotrophic bacterioplankton indicator species of the main bloom stage include OTUs representing both the phycosphere of colonial cyanobacteria and free-living species. Among the protists, sessile ciliates benefit most from plenty of substrates for colonization, while cyanobacterial grazers and parasites were minor. Overall, the cyanobacterial bloom creates new niches for the plankton community and significantly modifies its structure. Full article

In recent decades, there have been frequent occurrences of paralytic shellfish toxin (PST) contamination in the Yellow and Bohai Seas, China. The waters around Changdao Island, situated at the convergence of these two seas, have suffered harmful algal blooms of Alexandrium spp., indicating a potential risk of PST contamination in shellfish. However, a systematic investigation and assessment of PSTs in this area is still lacking. The presence of PSTs in plankton concentrates and shellfish in coastal areas of Changdao Island was monitored from April to October 2022, using liquid chromatography–tandem mass spectrometry. The potential toxin-producing microalgae were analyzed, as were the environmental conditions associated with their occurrence. The highest levels of PSTs in plankton concentrates and shellfish were both observed in September, reaching levels of 105.8 ng STXeq./L and 114.7 μg STXeq./kg, respectively. The main analogues were C1, C2, and GTX1–4. High-throughput analysis of the plankton concentrates identified eight species of Alexandrium, which are potential producers of PSTs. Sediment samples also revealed the presence of permanent cysts of Alexandrium. This research represents a significant advance in our understanding of the distribution and hypothetical sources of PSTs in the coastal waters of Changdao Island. Full article

The hypothesis that disturbance to coral reefs creates new surfaces that increase the risk of ciguatera is premised upon the increased algal substrates that develop on these surfaces being colonised by high ciguatoxin (CTX)-producing Gambierdiscus species that proliferate and enter the ciguatera food chain. Current evidence indicates that new algal substrates are indeed rapidly colonised by Gambierdiscus. However, the requirement that these Gambierdiscus species include at least one that is a significant (high) CTX-producer is more likely a limiting step. While ambient environmental conditions impact the capacity of Gambierdiscus to bloom, factors that limit the growth of the bloom could influence (typically increase) the flux of CTX entering marine food chains. Additionally, new algal substrates on damaged reefs can be preferentially grazed to funnel ciguatoxins from Gambierdiscus to herbivores in disturbed reef areas. In societies consuming second trophic level species (herbivores, grazers, and detritivores), such funnelling of CTX would increase the risk of ciguatera, although such risk would be partially offset over time by growth (toxin-dilution) and depuration. Here, we review evidence for six potential mechanisms to increase ciguatera risk from disturbance to coral reefs and suggest a hypothesis where ecosystem changes could increase the flux of CTX to groupers through a shift in predation from predominately feeding on planktonic-feeding prey to mostly feeding on benthic-feeding prey, increasing the potential for CTX to accumulate. Evidence for this hypothesis is stronger for the Pacific and Indian Oceans, and it may not apply to the Caribbean Sea/Atlantic Ocean. Full article