Search Results (716)

Saxitoxin (STX), produced by certain harmful algal bloom (HAB) species, bioaccumulates through the food chain and can cause paralytic toxicity in humans, potentially resulting in fatal outcomes. To date, STX detection has primarily been conducted under laboratory-controlled conditions, and the availability of a gold-standard method for the proactive monitoring and prevention of HAB-induced secondary damage remains limited. Therefore, the present study introduces an electrochemical-based biosensor that is capable of early monitoring of STX in HAB-occurred environments. The conserved region of sxtA4, a nucleic acid precursor that is essential for STX biosynthesis, is immobilized on the sensing membrane surface in a sandwich structure. In this process, target detection is recognized as an electrochemical signal by a methylene blue-labeled detection probe, and the reliability of biosensing is supplemented by an electrochemical trend that is opposite to DNA binding. The application of an alternating current electrochemical flow technique achieves more sensitive detection at attomolar levels and rapid measurement within 10 min than a conventional DNA biosensor based on hybridization. In addition, the designed biosensing structure selectively detects STX-synthesizing and non-synthesizing dinoflagellates significantly. The proposed platform can utilize the identification of STX-induced secondary damage of HAB and provide insight into a field-ready biosensor based on its characterization and detection performance. Full article

The complex ocean dynamics in the Northwest Pacific high-seas fishing grounds shape phytoplankton communities, which serve as the foundation for commercially pelagic species. This study investigates how mesoscale eddies modulate phytoplankton groups’ structures by analyzing the spatiotemporal evolution of eight phytoplankton functional types (PFTs) from 2014 to 2023. Utilizing high-resolution AI-driven model data (AIGD-PFT) and a normalized radial distance grid (0–2 R), we quantified PFTs concentrations within cyclonic (CE) and anticyclonic (AE) eddies, validated by Biogeochemical Argo (BGC-Argo) and in situ measurements. Results reveal that diatoms and dinoflagellates dominate the region, accounting for 88.7% of phytoplankton with distinct seasonal peaks in spring and autumn, respectively. CE significantly enhance diatom and dinoflagellate concentration, particularly within the 0.4 R–1.2 R dynamic ring, while AE favor the aggregation of picophytoplankton, such as Prochlorococcus, in mid-to-low latitudes. Correlation analysis indicates that diatom abundance is strongly linked to dissolved oxygen and negatively correlated with sea surface height. We conclude that mesoscale eddies drive the spatial remodeling of phytoplankton communities by altering local physical and nutrient conditions. These findings provide a critical ecological context for assessing the habitat distribution and sustainable management of North Pacific fisheries across different trophic levels. Full article

Marine mucilage events are intensifying in semi-enclosed seas under accelerating climate- and nutrient-driven pressures, yet their ecosystem-level consequences for aquaculture-linked coastal habitats remain insufficiently documented. This study provides an integrated spatiotemporal assessment of water quality, phytoplankton community structure, and biometric responses of Mytilus galloprovincialis during and after the 2025 mucilage outbreak in the Gulf of Erdek (Sea of Marmara, Türkiye). Mucilage accumulation was associated with sharp increases in turbidity, total suspended solids, and particulate organic matter, alongside declines in dissolved oxygen and pH. Phytoplankton assemblages exhibited marked seasonal restructuring: the mucilage period was characterized by the coexistence of mucilage-forming taxa, non-toxic bloomers, and multiple harmful algal bloom (HAB) groups, including DSP- and ASP-related species, whereas post-mucilage conditions were dominated by non-toxic diatoms with substantially reduced HAB representation. The dinoflagellate species representing the May period in terms of abundance were Noctiluca scintillans and Prorocentrum micans; the diatom species were Chaetoceros radiatus, Cylindrotheca closterium, Pseudo-nitzschia pseudodelicatissima, and Thalassiosira rotula; and the coccolithophore was Phaeocystis pouchetii. Mussel biometric analyses revealed biometric indices and condition values markedly below regional historical baselines during the mucilage event, alongside reduced meat yield, followed by pronounced compensatory growth during the post-mucilage period. Our findings demonstrate that mucilage acts as both a physical and biological stressor, driving short-term ecological shifts in phytoplankton diversity and imposing substantial but reversible physiological impacts on mussel stocks. These results underscore the need for continuous biodiversity monitoring frameworks that integrate mucilage dynamics, HAB occurrence, and aquaculture resilience in regions vulnerable to climate-enhanced organic aggregate formation. Full article

The cell membrane serves as the first line of defense against adverse environmental factors and is first to adapt to changing conditions. Cell membranes in both coral and its symbionts, which use different membrane adaptation strategies, have to acclimatize to various abiotic stressors. As our molecular-genetics analysis showed, colonies of Junceella fragilis were associated with dinoflagellates Cladocopium thermophilum, Gerakladium endoclionum and Breviolum minutum. We analyzed the phospholipid (PL) molecular species of the wild and cultivated Junceella fragilis and their dinoflagellates (phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI), ceramideaminoethylphosphonate (CAEP)), as well as thylakoid membrane lipids of dinoflagellates (glycolipids and betaine lipids). When comparing wild and cultivated J. fragilis colonies, there were no significant differences in thylakoid lipids, but there were differences in host membrane phospholipids, namely in PC, PE and PS. Thus, the profile of PL molecular species of the membrane is very sensitive to environmental factors, which probably explains the observed differences in the profiles of molecular PL species in this study. Full article

Water dynamics and nutrients are widely recognized as the main triggers of phytoplankton blooms. These factors may control the stability of marine ecosystems. Penzhina Bay and the Shelikhov Gulf are famous for their high tidal dynamics in comparison with the basins of the World Ocean and for being the feeding places of Bowhead whales. Here, we study the dynamics and thermohaline structure of water; nutrients; isotopic signatures of δ¹⁵N–$\mathrm{N}{\mathrm{O}}_3^{-}$ and δ¹⁸O–$\mathrm{N}{\mathrm{O}}_3^{-}$; as well as chlorophyll a in Penzhina Bay, the Shelikhov Gulf, and the Penzhina River to understand the features of an ecosystem with intense tidal dynamics in the subpolar region. This work is based on data obtained in three cruises of the R/V “Akademik Oparin” in the period from 2023 to 2025, with speed boat observations in the Penzhina River from May to October, including the flooding peak in June. The observations covered cases with tides from 7 to 13.4 m in height. The interaction between tides and river runoff was observed to supply dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus (DIP) from the sea and dissolved silicate (DSi) from the river. The “white nights” in July, combined with the increased supply of nutrients, are good conditions for phytoplankton blooms, and as a result, the concentration of chlorophyll a in the study area was observed to be up to 39 µg/L. High primary production supports the food chain, and this is probably the main reason why Bowhead whales come to feed in the summer. The DIN/DIP ratio indicates DIN as a limiting factor in most of Penzhina Bay and throughout the Shelikhov Gulf. At the same time, the DSi/DIP ratio at a significant distance from the mouth of the Penzhina River is close to 0, indicating unfavorable conditions for diatoms. The DSi limit can cause the blooming of dinoflagellates, which sometimes occurs in this region. Full article

Phytoplankton is a key component of marine ecosystems and a sensitive indicator of environmental change. In this study, light microscopy (LM) and DNA metabarcoding (18S-V4, 18S-V9, and rbcL) were combined to assess differences in phytoplankton diversity and community structure across three LTER sites in the northern Adriatic Sea, and to evaluate the methodological effects on community assessment. A total of 329 genera and 527 species were recorded by integrating both the approaches. Metabarcoding (MB) revealed increased taxonomic richness than LM, particularly for dinoflagellates and small phytoflagellates, while LM was better for identifying the diatoms and coccolithophores. The rbcL marker improved the taxonomic resolution for the diatoms compared to the 18S regions. The proportion of species shared among the sites increased from 13% with LM to 33–42% with MB, suggesting that MB may effectively reduce the discrepancies observed when relying solely on LM. Cluster analysis performed on species-relative abundances grouped the samples by approaches rather than sites, showing that methodological variability exceeded the ecological differences. The relative abundance patterns differed between methods but became more comparable after applying correction factors based on the 18S rRNA gene copy numbers, particularly for the dinoflagellates. Overall, MB enhances biodiversity assessment and comparability among sites, while LM remains essential for morphological validation and for abundance assessment. Full article

We evaluated the algicidal properties of Bacillus Ba3 fermentation broth combined with clay for harmful algae bloom (HAB) control through in situ enclosure experiments in Suao Bay, China. It was indicated by the results that the combination significantly reduced HAB abundance, turbidity and phosphorous in water without affecting zooplankton and small fish. The treatment achieved 99.8% (Phase 1) and 100% (Phase 2, with sediment) removal rates for harmful dinoflagellates, primarily Prorocentrum donghaiense and Karenia mikimotoi, while demonstrating high taxonomic selectivity, allowing beneficial diatom populations such as Chaetoceros spp. to remain resilient. This synergy is attributed to clay acting as a physical carrier that brings adsorbed algicidal metabolites into direct, prolonged contact with algal membranes. This method shows promise for prolonged dinoflagellate control and may offer an economical and environmentally sound approach to HABs. More research is needed to establish its action on a wider scale in marine environments. Full article

Harmful algal blooms have occurred more frequently in recent decades and threaten aquaculture, tourism and human health. As a promising control method, most studies on allelopathic mechanisms have focused on the physiological effects on harmful algae. This study employed a multiomics approach to investigate the allelopathic response of the dinoflagellate Scrippsiella acuminata to the allelochemical protocatechuic acid, a phenolic compound known for its inhibitory effects on algal growth. Using transcriptomic, proteomic, and metabolomic analyses, we identified significant changes in gene expression (5247 upregulated and 81 downregulated), protein expression (56 upregulated and 49 downregulated), and metabolite profiles (320 upregulated and 168 downregulated) in response to allelochemical stress. Transcriptomic data revealed an upregulation of genes associated with antioxidant systems and energy metabolism, suggesting a potential antioxidant response to protocatechuic acid exposure. Proteomic analysis highlighted the impact on photosynthesis, energy metabolism, and genetic information processing, with a particular emphasis on the modulation of lipid and carbohydrate metabolism to adapt to stress. Metabolomic profiling corroborated these findings, demonstrating shifts in lipid and amino acid metabolism indicative of an adaptive strategy for energy storage and maintenance of cellular homeostasis under allelochemical stress. Notably, alterations in photosynthesis-related proteins and metabolites indicated a direct effect of protocatechuic acid on the photosynthetic machinery, potentially impairing algal growth and energy production. In conclusion, our multiomics analysis provides a comprehensive view of the complex response of S. acuminata to allelochemical stress, revealing the intricate interplay among genetic, proteomic, and metabolic adjustments. These insights contribute to the understanding of allelopathic interactions and offer potential avenues for the development of novel strategies to manage harmful algal blooms. Full article

Phytoplankton communities are crucial for sustaining the high biodiversity and productivity of estuarine ecosystems, yet these regions are increasingly impacted by anthropogenic activities. To elucidate the impacts of anthropogenic pressures, this study characterized the seasonal dynamics of the phytoplankton community in the outer Yangtze River Estuary using an environmental DNA (eDNA) metabarcoding approach. We identified 279 and 306 phytoplankton genera in summer and autumn, respectively. Community composition differed more between seasons than within them, with dinoflagellates, chlorophytes, and diatoms dominating both periods. The phytoplankton community structure showed higher richness, diversity, and stability during autumn than in summer. Furthermore, redundancy analysis identified DIN/DIP, temperature, salinity, orthophosphate (PO₄³⁻), ammonia nitrogen (NH₄⁺), and depth as primary drivers, with DIN/DIP being the core factor structuring the phytoplankton assemblage. These results suggest that phosphorus limitation may drive the shift in phytoplankton community structure from diatom to dinoflagellate dominance, due to varying phosphorus utilization strategies among different phytoplankton. These findings provide novel insights into the impacts of anthropogenic activities on estuarine ecosystems and offer science-based guidance for managing nitrogen and phosphorus inputs to support global sustainable development goals. Full article

For the first time in the bay of Annaba (Southern Mediterranean), we studied the spatiotemporal distribution of potentially toxic benthic dinoflagellates: Ostreopsis cf. ovata, Prorocentrum lima, Coolia monotis, and Amphidinium carterae, hosted by the dominant macrophytes Posidonia oceanica, Padina pavonica, Codium fragile, and Halopteris scoparia. Sampling of these macrophytes was conducted weekly during spring and summer as well as bi-weekly in autumn and winter, from October 2022 to November 2023, at contrasting sites within Annaba Bay. The measured environmental parameters included temperature, pH, dissolved oxygen, salinity, ammonium, nitrate, nitrite, dissolved organic nitrogen, dissolved inorganic nitrogen, phosphate, dissolved organic phosphorus, silicate, and chlorophyll a. A proliferation of O. cf. ovata was recorded in July 2023, coinciding with a marked increase in temperature, with a maximum abundance exceeding 40 × 10³ cells g⁻¹ of fresh weight (FW) on H. scoparia and C. fragile. The maximum abundance of P. lima reached 8700 cells g⁻¹ FW on H. scoparia during July and August 2023. Coolia monotis exhibited a peak of 2800 cells g⁻¹ FW on H. scoparia. The abundance of A. carterae increased with temperature, reaching a maximum of 980 cells g⁻¹ FW on P. pavonica. The distribution of epiphytic dinoflagellates varied according to the macrophyte substrate. Overall, statistical analyses indicate that benthic dinoflagellate community structure is shaped by the combined effects of temperature, nutrient availability, and ecological niche differentiation, with temperature emerging as the dominant driver. This suggests that climate-driven increases in Mediterranean Sea surface temperatures are likely to extend the seasonal window of harmful benthic algal blooms, thereby enhancing ecological disturbances and potential risks to human health. This study provides the first assessment of BHAB dynamics along the Eastern Algerian coast, highlighting the role of ongoing regional warming in shaping future bloom patterns. Full article

Palynological analysis of seventy-seven cutting samples from six boreholes in the Marañón Basin (northeastern Peru) has identified five distinct Neogene marine incursion events (ME-1 to ME-5), challenging existing models that depict them as short-lived episodes. The diverse palynological assemblages, comprising spores, pollen, freshwater algae, and critical marine indicators—including dinoflagellate cysts, foraminiferal test linings, and copepod eggs—reveal that these incursions were protracted and recurrent, each associated with a maximum flooding surface and bounded by intervals of continental sedimentation. The stratigraphic record shows the earliest event ME-1 (Aquitanian to Late Burdigalian, 23.03–17.7 Ma) identified across all studied wells. ME-2 (latest Burdigalian to Middle Langhian, 17.0–16.1 Ma) is also recorded basin-wide. ME-3 (latest Burdigalian to earliest Langhian 16.5–15.7 Ma) registered in two wells. ME-4 (Late Langhian to latest Serravallian, 14.6–11.62 Ma) registered in only two wells and ME-5 (Early Tortonian, 11.6–10 Ma) is documented exclusively in the southernmost well, culminating in Zanclean (~5.5–3.6 Ma) mangrove development. We interpret the ingress routes for ME-1 to ME-3 to be westward via the Marañón Portal or northward from the Caribbean, associating them with the Proto-Pebas and Pebas systems. In contrast, ME-4 would also be from Amazon trunk or Paraná Portal associated with the Pebas Phase, and ME-5 likely originated from the south through the Paraná Portal, linking it to the Acre Phase. These results demonstrate that Miocene marine incursions into western Amazonia were not brief episodes but represented prolonged periods of marine influence, facilitated by sustained subsidence in the Marañón retro-arc foreland basin. This history reveals a dynamic connectivity throughout the Neogene, with marine conditions acting as persistent biogeographic barriers that critically shaped the region’s Miocene biodiversity patterns. This refined chronology provides a comprehensive regional framework, significantly advancing our understanding of Amazonian paleogeography. Full article

Active substance-based Ballast Water Management Systems (BWMS) can generate disinfection by-products (DBPs) by reacting with dissolved organic matter (DOM). However, current IMO G9-based assessments often overlook qualitative DOM variations. This study investigated DBP formation following NaDCC treatment in natural seawater dominated by the diatom Skeletonema costatum and the dinoflagellate Akashiwo sanguinea. Laboratory-cultured DOM was also analyzed using ATR-FT-IR, PCA, and 2D-COS to evaluate structural differences. In field experiments, S. costatum treatment primarily produced brominated trihalomethanes (THMs) and specific haloacetic acids (HAAs) with a limited composition. Conversely, A. sanguinea treatment yielded a diverse range of DBPs, including nitrogenous DBPs (HANs). FT-IR results, supported by 2D-COS, revealed that A. sanguinea-derived DOM underwent non-monotonic structural changes and distinct sequential functional group reactions, suggesting multiple, time-delayed precursor interactions. These findings demonstrate that phytoplankton species-specific DOM composition significantly dictates DBP profiles and temporal dynamics. Therefore, environmental risk assessments for BWMS must incorporate the qualitative characteristics of biogenic DOM and dominant species traits, particularly during coastal bloom events, to ensure more accurate management strategies. Full article

Blooms of the marine dinoflagellate Vulcanodinium rugosum have been associated with skin lesion outbreaks in Cuba and elsewhere. In this study, cell growth and toxin production were investigated under laboratory-controlled conditions in two strains isolated from Cienfuegos Bay, Cuba. Strains were cultured with and without a mechanical agitation and toxins were analyzed at two stages of the culture growth (exponential and stationary). Although blooms in Cienfuegos Bay occur in a semi-enclosed system characterized by calm waters with no agitation, the results of this study suggest that V. rugosum cells may also exhibit growth capacity under agitated conditions, or in open waters, comparable to that observed in systems with low hydrodynamic energy. Higher toxin levels, as determined by liquid chromatography with mass spectrometry (LC-MS/MS), were detected after exponential growth. Portimine-A and pinnatoxin-F (PnTX-F) were the dominant toxins (up to 1.75 and 1.0 pg·cell⁻¹, respectively). PnTX-E, -D and Portimine-B were also detected at minor concentrations. This study contributes the first data necessary for a proper interpretation of monitoring programs aiming to assess the impact of V. rugosum blooms, particularly when used alongside forecasting models. Full article

Symbiotic dinoflagellates from the family Symbiodiniaceae play a central role in coral reef ecosystems by forming mutualistic relationships with reef invertebrates, particularly stony corals. These relationships underpin reef productivity in nutrient-poor waters but are vulnerable to disruption from marine heatwaves and climate change. While laboratory culturing of symbionts has enabled controlled studies of thermal stress, prolonged culturing may lead to physiological changes that do not reflect in hospite conditions. Here, we examined the thermal stress responses of two axenic cultures of Symbiodinium A1, freshly isolated and long-term cultured (2.5 years), originally from the jellyfish Cassiopea andromeda in the Red Sea. Both cultures were exposed to a daily temperature increase of 1 °C, up to 37 °C. Freshly isolated symbionts consistently showed higher photochemical efficiency (0.515 ± 0.007) and growth rates (1.68 ± 0.60 µ day⁻¹) compared to long-term cultured cells (0.401 ± 0.007; −2.25 ± 0.38 µ day⁻¹), which collapsed at 37 °C. Heat stress also led to decreases in O₂ and increases in pCO₂ across treatments. Long-term cultured symbionts exhibited greater lipid body accumulation, suggesting a shift to anaerobic metabolism. These findings demonstrate that extended batch culturing alters symbiont physiology and stress responses, highlighting the need to consider culture history in experimental designs to avoid bias in interpreting holobiont resilience. Full article

The dinoflagellate Akashiwo sanguinea is a prominent harmful algal bloom (HAB) species responsible for significant mortalities of marine fauna. Its life cycle, which includes a benthic resting cyst stage, is fundamental to its bloom dynamics and geographic dispersal. This study investigates the effects of Taebaek coal powder, a silicate-rich mineral supplement, on the growth and life-stage transitions of A. sanguinea. Cultures were grown in standard f/2 medium (control) and f/2 medium amended with an extract of the coal powder. We monitored culture performance using fluorometry for quantitative biomass assessment and imaging flow cytometry (FlowCam) for qualitative life-stage analysis. The coal powder amendment conferred a distinct advantage, promoting both vegetative proliferation and the formation of resting cysts. Fluorescence-based measurements showed that the coal powder-amended cultures reached a density equivalent of 3851 ± 214 cells mL⁻¹ by day 4, significantly outpacing the control (2963 ± 351 cells mL⁻¹). Peak vegetative abundance in the treated cultures reached 6967 ± 423 cells mL⁻¹ on day 14, compared to 5979 ± 288 cells mL⁻¹ in the control. Critically, resting cyst production was substantially enhanced in the coal powder treatment, with densities reaching 32–37 cysts mL⁻¹ by the end of the experiment, compared to 22–26 cysts mL⁻¹ in the control. These findings demonstrate that mineral supplementation with Taebaek coal powder can significantly augment both vegetative growth and encystment in A. sanguinea, suggesting a potential link to micronutrient availability, though the underlying mechanisms remain to be elucidated. This enhanced cyst production method may prove valuable for harvesting cysts for ecophysiological research and highlights the need to explore how mineral-induced life-cycle shifts could influence bloom dynamics in a context-dependent manner. Full article