Search Results (474)

The mucilage phenomenon consists of the appearance of large gelatinous aggregates floating in the water column. In summer 2024, this event has reappeared in the Northern Adriatic Sea (NAS) on a large scale. This study provides an integrated characterization of the microalgal community within mucilage aggregates and surrounding waters in two NAS areas (Gulf of Trieste and Conero Riviera) using light microscopy (LM), metabarcoding (MB) based on ribosomal 18S V4 and V9 markers, and scanning electron microscopy (SEM) for selected taxa identification. Mucilage aggregates acted as dynamic microbial hotspots, hosting a rich diatom community, with abundances 1–2 orders of magnitude higher than in the surrounding water. Dominant diatom species were Cylindrotheca closterium, Nitzschia spp., Nitzschia gobbii, and Thalassionema nitzschioides. Some phytoflagellates (e.g., Tetraselmis spp.) and dinoflagellates (e.g., Karlodinium veneficum, Pseliodinium fusus, and Wangodinium sinense) were detected exclusively by MB, while LM and SEM revealed species missed by other approaches. Gonyaulax fragilis, one of the species indicated as an important mucus producer, was present at the onset and throughout the phenomenon, as detected by LM and MB. The integrated approach improves knowledge of microalgal communities in NAS mucilage. Full article

Massive phytoplankton blooms threaten lake ecosystems, causing significant ecological and socio-economic damage. While remote sensing is vital for monitoring, the vertical stratification of algae influences light propagation and distorts remote sensing reflectance signals. This effect is particularly understudied in high-latitude lakes, leaving a gap in understanding phytoplankton biomass patterns. To address this, our study investigated three high-latitude water bodies: Lake Hulun, Fengman Reservoir, and Lake Khanka. We collected water samples from three depths based on total and euphotic zone depth and developed layer-specific inversion models for chlorophyll-a (Chal) and phycocyanin (PC) using a random forest algorithm. These models demonstrated strong performance and were applied to Sentinel-3 OLCI imagery from 2016–2024. Our results show that Chla generally decreases exponentially with depth, whereas PC exhibits a Gaussian-like vertical distribution with a pronounced subsurface maximum at approximately 1 m. In addition, a significant positive correlation between Chla and PC was observed in surface waters. In Lake Khanka, the northern basin exhibited a significant interannual increase in phytoplankton biomass. At 3 m, PC correlated negatively with turbidity and responded strongly to cyanobacterial blooms, while organic suspended matter correlated positively with Chla. This work establishes a robust framework for multilayer water quality monitoring in high-latitude lakes, providing critical insights for eutrophication management and cyanobacterial bloom early warning. Full article

This study presents the first comprehensive assessment of microalgal diversity in two Slovenian transitional waters (TWs): the shallow brackish lagoon of the Škocjanski Zatok Nature Reserve (SZNR) and the Rižana River estuary within the Port of Koper (PK) area. Between 2018 and 2021, water samples collected with a phytoplankton net were analyzed using light and scanning electron microscopy. In total, 240 species from 117 genera were identified in TW, dominated by diatoms and dinoflagellates, surpassing the diversity at a marine coastal station (91 species, 59 genera). Species richness was higher in PK (226) than in SZNR (154), mainly due to dinoflagellates and coccolithophores. Marine taxa predominated along the salinity gradient, with moderate contributions from brackish taxa and few freshwater forms, reflecting both natural and anthropogenic influences. Planktonic taxa dominated at all sites, while benthic forms were abundant in the lagoon, particularly in spring. Thirty-two taxa were recorded for the first time in Slovenian TW, mostly benthic or tychopelagic diatoms. The detection of Coolia monotis and five cyanobacterial genera with potentially harmful traits highlights the role of TW as an ecological interface. The taxonomic sufficiency analysis showed that the order level is sufficient to distinguish transitional from marine assemblages, beyond which ecological information is lost. Overall, this study highlights the importance of detailed taxonomic resolution for detecting microalgal diversity, including harmful and non-indigenous species to ensure robust ecological assessments under the WFD and MSFD directives. Full article

As a key freshwater wetland in the Beijing–Tianjin–Hebei core area, Baiyangdian Lake’s ecological health is strategically significant for regional ecological security, prompting this study to explore how sediment phosphorus forms drive its phytoplankton communities. The research adopted sequential extraction technology, morphological identification, and multivariate statistics in Baiyangdian Lake. Results showed sediment phosphorus was dominated by highly active exchangeable phosphorus (Ex-P, ~60%, with higher levels around villages of lake center and western areas), with occluded phosphorus (Oc-P, ~23%) as the second most abundant form. Ex-P was the core factor shaping phytoplankton communities, directly increasing biomass density (r = 0.38, p < 0.05) and explaining 17.92% of community variation. Bacillariophyta was the dominant group (43.3%), while calcium-bound phosphorus (Ca-P) maintained diversity and aluminum-bound phosphorus (Al-P) inhibited evenness (r = −0.35, p < 0.05). Active phosphorus directly affected, and inactive phosphorus indirectly regulated, phytoplankton patterns, clarifying the unique phosphorus structure of northern carbonate-type lakes and filling research gaps. It is suggested to include Ex-P and Ca-P in aquatic ecological monitoring and prioritize sediment passivation and riparian restoration in high-Ex-P areas to mitigate algal bloom risks. Full article

Based on multi-seasonal surveys (2020–2022) in Beihai Silver Beach, this study examined phytoplankton community dynamics and environmental drivers. Results showed persistent diatom dominance, with Skeletonema costatum as the predominant species and a major bloom in autumn 2021. Species richness peaked in summer and was lowest in winter, while abundance hotspots were associated with the Fengjia River estuary. Generalized Additive Models identified reactive phosphate as the primary driver, exhibiting nonlinear relationships with species richness (R² = 0.91) and diversity (R² = 0.436). Dissolved oxygen also had significant nonlinear effects. A counterintuitive positive correlation between lead concentration and species richness highlighted complex stressor interactions. This study emphasizes phosphorus control for eutrophication mitigation and demonstrates GAMs’ utility in detecting nonlinear ecological responses, supporting science-based management of coastal ecosystems. Full article

In the summer of 2022, massive blooms of the toxic haptophyte Prymnesium parvum triggered one of the most significant ecological disasters ever recorded in the Odra River, resulting in massive fish and mollusk kills and severe economic damage. Having shown promise for treating other types of phytoplankton blooms, we applied various concentrations of hydrogen peroxide (HP) in an experimental setting using waters collected from the Gliwice Canal; a location with extensive proliferations of P. parvum. In the first stage of our experiment, a single application as low as 14 mg H₂O₂/L successfully reduced P. parvum biomass and prymnesin concentrations, measured using newly obtained prymnesin standards, with limited negative impact on other phytoplankton. In the second stage of the experiment, we reintroduced an inoculum of the canal water containing the haptophyte bloom. The simulated renewal of the phytoplankton community led to higher P. parvum biomass and elevated prymnesin concentrations, possibly due to nutrient release after HP application or reduced phytoplankton competition. We observed differences in the toxin profile compared with control conditions, suggesting changes in the haptophyte ecotypes in the experimental treatments. The results suggest that HP can be successfully used to combat P. parvum blooms, though caution is warranted with higher concentrations. Full article

Many lakes worldwide, including in China’s Yangtze River Basin, face eutrophication, which reduces phytoplankton diversity and increases bloom risk. Following severe pollution, these Chinese lakes have undergone substantial control and regulation. However, the efficacy of these measures is still unclear. Focusing on Lake Chaohu as a representative case, this study investigated the seasonal phytoplankton dynamics (2022–2023) under concurrent nutrient reduction and a fishing ban. The annual mean concentrations of total nitrogen, total phosphorus, and chlorophyll a were 1.57 mg/L, 0.184 mg/L, and 21.21 μg/L, respectively. The phytoplankton community was dominated by Cyanobacteria, which constituted approximately 75% of the total biomass. Co-occurrence network analysis revealed lower community stability during these warm, Cyanobacteria-dominated periods. Statistical analyses identified total phosphorus and temperature as key drivers, confirming bottom-up control via nutrient limitation as the fundamental mechanism. However, extreme heat events may have partly offset the benefits of nutrient reduction by promoting cyanobacterial dominance, which can decrease phytoplankton diversity. A recorded decrease in phytoplankton phosphorus use efficiency after the fishing ban suggests a potential strengthening of top-down control. These findings highlight that sustained nutrient load reduction is essential to reduce cyanobacterial bloom risk, while continued enforcement of the fishing ban may enhance the regulatory effect of top-down control on cyanobacterial blooms, thereby improving the stability and diversity of phytoplankton communities. Full article

Accurate monitoring of chlorophyll-a (Chl-a) is essential for managing coastal aquaculture, as Chl-a indicates phytoplankton biomass and water quality. This study developed a hybrid deep learning model integrating convolutional neural networks (CNN), bidirectional long short-term memory (BiLSTM), and an attention mechanism (Attention) to classify Chl-a using hourly, water quality datasets collected from the GOT001 station in Si Racha Bay, Eastern Gulf of Thailand (2020–2024). A random forest (RF) identified sea surface temperature (SEATEMP), dew point temperature (DEWPOINT), and turbidity (TURB) as the most influential variables, accounting for over 90% of the accuracy. Chl-a concentrations were categorized into ecological groups (low, medium, and high) using quantile-based binning and K-means clustering to support operational classification. Model performance comparison showed that the CNN–BiLSTM model achieved the highest classification accuracy (81.3%), outperforming the CNN–LSTM model (59.7%). However, the addition of the Attention did not enhance predictive performance, likely due to the limited number of key predictive variables and their already high explanatory power. This study highlights the potential of CNN–BiLSTM as a near-real-time classification tool for Chl-a levels in highly variable coastal ecosystems, supporting aquaculture management, early warning of algal blooms or red tides, and water quality risk assessment in the Gulf of Thailand and comparable coastal regions. Full article

Cape Town, South Africa, experiences coastal upwelling during austral summer. In this study, the effects of kinematic and thermal ‘roughness’ on wind stress are analyzed using 5–25 km resolution multi-satellite and coupled reanalysis datasets in the period 2010–2024. Average conditions for austral summer (December–February) are calculated to identify east–west gradients in sensible heat flux, wave height, and equatorward winds and to assess their consequences for the drag coefficient, wind-driven Ekman transport, and entrainment over the shelf from 16.9 to 18.7° E, north of Cape Town (33.7° S). Statistical and numerical outcomes are compared for austral summer and during active coastal upwelling in January 2018 with chlorophyll concentrations > 3 mg/m³. A subtropical anticyclone generated shallow equatorward winds next to a wind shadow north of Cape Town. Sharp cross-shore gradients in momentum flux were amplified by shoreward reductions in sensible heat flux and wave height, which suppressed the drag coefficient 10-fold. The inclusion of kinematic and thermal roughness in wind stress calculations results in a higher average cyclonic curl (−2.4 × 10⁻⁶ N/m³), which translates into vertical entrainment > 3 m/day at 33.7° S, 18° E. The research links coastal upwelling leeward of a mountainous cape with cross-shore gradients in air–sea fluxes that support recirculation and phytoplankton blooms during austral summer. Full article

Responses of size-fractionated phytoplankton to environmental variables—particularly temperature, euphotic depth, and ammonium—were investigated in Gwangyang Bay to identify the phytoplankton groups responsible for estuarine blooms. Carbon-normalized biomass clearly showed the dominance of nanoplankton during summer and microplankton during winter. A combination of microscopy and flow cytometry analyses revealed that cryptophytes dominated the summer bloom, whereas diatoms dominated the winter bloom. Polynomial regression models indicated that diatom-dominated microplankton biomass declined sharply with increasing temperature and ammonium, while cryptophyte-dominated nanoplankton and cyanobacteria-dominated picoplankton biomass increased with rising temperature and decreased with increasing euphotic depth. These results highlight the substantial role of small phytoplankton (nanoplankton and picoplankton) in the bay ecosystem, where concerns over declining water quality and reduced nitrate availability are ongoing. Full article

Environmental filtering studies have revealed immense oceanic microbial diversity, yet the Southeast Pacific remains comparatively undersampled. We characterize the molecular diversity of phytoplankton across two biogeographic domains with contrasting oceanography—fjords and channels (41–53° S) versus the open Pacific (36–42° S)—where the frequency and intensity of harmful algal blooms (HABs) have increased. Using SSU rRNA metabarcoding, we retrieved community composition and biogeographic patterns for micro-phytoplankton. Diversity signals indicated broadly overlapping communities between domains with subtle shifts along hydrographic and nutrient gradients rather than sharp breaks. Phylogenetic resolution within bloom-forming genera recovered well-supported clades, and multiple ASVs matched historically relevant HAB taxa, including representatives of the Alexandrium complex, Dinophysis, Pseudo-nitzschia, and Karenia. Together, these results suggest that regional environmental filtering acts modestly at the community level while preserving clear signals of taxa of management concern. By providing a regionally resolved, DNA-based baseline for southern Chile’s fjords and adjacent open coast, this study helps fill the molecular diversity gap for the Southeast Pacific and supports improved HAB surveillance and ecosystem forecasting in a climate-sensitive seascape. Full article

The intensification of eutrophication in global water bodies has exacerbated the occurrence of cyanobacterial blooms, whose secondary metabolites can have detrimental effects on animals, humans, and ecosystems. This study analyzed and statistically evaluated the species composition and distribution of phytoplankton, assessed the concentration of anatoxin-a (ATX-a) in environmental and biological samples (n = 261), and explored the spatial distribution and bioaccumulation of ATX-a in Hulun Lake (Inner Mongolia, China). In late July 2024, the cyanobacteria Dolichospermum spp. comprised 85.5% of the total phytoplankton density. ATX-a levels were vertically distributed with higher concentrations in deeper water (3 m; 146.69 ± 11.84 ng·L⁻¹) and sediments (3.28 ± 0.45 ng·g⁻¹ dry weight) as compared to surface layers (0.5 m; 132.46 ± 8.19 ng·L⁻¹). In fish, bioaccumulation of ATX-a was greatest in the liver (2.37 ± 1.85 ng·g⁻¹), followed by intestinal contents (1.83 ± 0.74 ng·g⁻¹), with minimal accumulation in muscle tissues (1.74 ± 0.77 ng·g⁻¹). ATX-a levels were higher in smaller fish (minnows) than larger fish (Predatory carp, Gibel carp, and European carp). Additionally, all fish tissue samples contained ATX-a, suggesting that aquatic organisms were continuously exposed to ATX-a throughout the summer. A biodilution of ATX-a was observed from phytoplankton (384.82 ± 176.82 ng·L⁻¹) to zooplankton (1.27 ± 0.12 ng·g⁻¹), followed by biomagnification from zooplankton to fish. Full article

Chlorophyll fluorescence provides direct insights into the physiological status of algae, contributing to the understanding of the marine carbon cycle. However, in situ measurements of phytoplankton photosynthetic physiology remain relatively scarce in the Yangtze River Estuary (YRE), an ecosystem under intense anthropogenic pressure. Consequently, quantifying composition and physiological status variations of phytoplankton in this region is critical for understanding their ecological functions and responses. Spring cruise revealed that the warm and high-salinity oceanic region exhibited a greater abundance of dinoflagellates and chrysophytes, while the lower-salinity plume region was characterized by higher abundances of chlorophytes and cryptophytes. Diatoms dominated across all regions. The highest chlorophyll a concentration (6.3 μg/L) was observed in the oceanic region. Chlorophyll fluorescence indicated that the warm offshore community was more active, suggesting favorable phytoplankton growth. As temperature decreased and seawater mixed, the maximum relative electron transport rate (rETRmax) and the minimal saturated light intensity (I_k) decreased, yet the overall community remained healthy. Despite the plume delivering abundant nutrients, phytoplankton activity was relatively low due to the cold spring water temperature. This study will provide a foundation for understanding phytoplankton dynamics under anthropogenic influences in the YRE and the adjacent East China Sea, supporting algal bloom monitoring and early warning efforts. Full article

Phytoplankton are fundamental to sustaining marine ecosystems and significantly influence the global carbon cycle. However, identifying their types accurately from satellite imagery remains a challenge. This study presents machine learning approaches for classifying phytoplankton types, including coccolithophores, diatoms, and dinoflagellates, using Second-generation Global Imager (SGLI) imagery aboard the GCOM-C satellite. Several algorithms were evaluated, with Random Forest (RF) and Gradient Tree Boosting (GTB) achieving the highest classification performance in classifying coccolitophores and diatoms. On the other hand, both RF and Classification and Regression Trees (CARTs) are effective for distinguishing dinoflagellates from surrounding water types. To assess model transferability, the developed machine learning models were applied in another sub-regions and on a different date of acquisition. The validation confirmed the ability of the model to generalize across sub-region and temporal variations in SGLI imagery. As a result, the potential of combined machine learning and SGLI imagery can improve phytoplankton detection, enabling large-scale monitoring at both regional and global levels. This paper highlights the importance of combining artificial intelligence with satellite-derived ocean color data to improve the monitoring of marine ecosystems. Full article

A growing body of evidence indicates that freshwater bodies, particularly eutrophic systems, are significant sources of the greenhouse gases (GHGs) carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). Unlike marine environments, freshwater systems are generally shallower and more directly influenced by terrestrial inputs, including nutrient enrichment, organic matter deposition, and steep redox gradients in both the water column and sediments. These conditions promote intense phytoplankton growth, including massive harmful cyanobacterial blooms (HCBs), and stimulate microbial processes that drive GHG production and release. This opinion article examines the biogeochemical mechanisms underlying these emissions and evaluates the potential of mitigation treatments to both enhance carbon sequestration and reduce CH₄ and N₂O emissions. We argue that effective control of HCBs, whether through nutrient load reduction or direct mitigation protocols, would not only provide communities with toxin-free water but also significantly lower GHG emissions from eutrophic waterbodies. As this is an opinion paper rather than a comprehensive review, we intentionally avoided citing widely accepted concepts, since doing full justice to the many excellent contributions across all relevant subfields would not be possible within the scope of this work. Full article