Phytoplankton community structure and harmful species in a North African coastal lagoon: the case of Moulay Bousselham, (Moroccan Atlantic)

Salinity and nutrient driven shifts in diatom dominance along the Tamil Nadu coast during the northeast monsoon.

Responses and drivers of phytoplankton to the anthropogenic water-sediment regulation in the Yellow River.

The subtropical Jiulongjiang River serves as a crucial water supply, yet it has been plagued by frequent blooms of the dinoflagellate genus Unruhdinium. To investigate the diversity and spatiotemporal dynamics of Unruhdinium species, we conducted seasonal sampling in Xipi Reservoir and large-scale sampling across the Beixi Creek of Jiulongjiang River from 2020 to 2021. Our cyst germination experiments revealed the cyst-theca relationships of U. minimum and U. kevei, along with the identification of two undescribed species. Unruhdinium minimum resembles Peridiniopsis kulczynskii in terms of cell size and plate pattern and probably is a junior synonym. Utilizing DNA metabarcoding to target the large subunit ribosomal RNA gene (LSU rDNA D1-D2) in both water and sediment samples, we detected seven species of Unruhdinium, with U. minimum, U. kevei, and U. penardii var. robusta emerging as the most dominant. Notably, U. minimum exhibited a preference for warm waters, while U. penardii var. robusta thrived in colder conditions. In contrast, U. kevei was predominantly observed in the spring. The alleviation of eutrophication and elevated nitrogen/phosphorus ratios may account for the decline of Unruhdinium blooms in the Jiulongjiang River since 2011. Our results enhance the possibility of dinoflagellate dynamics in freshwater systems and inform future conservation efforts in the subtropical rivers.

Phytoplankton community structure and its response to environmental factors in the cascade hydropower stations of the lower Jinsha River.

Anthropogenic nutrient inputs drove shifts in phytoplankton productivity and community structure in the northern South China Sea over the past century.

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.

Abstract The relationships between the functional diversity of phytoplankton and environmental conditions offer insights into phytoplankton community structure under environmental gradients in basins influenced by anthropogenic disturbances, including mining residues. Thus, we aimed to identify the main environmental drivers of the functional diversity of phytoplankton by considering three types of ecosystems and two distinct seasonal periods. We hypothesized that (1) ecosystems with higher hydrological stability and lower contamination—particularly deep lakes—support greater phytoplankton functional diversity, and (2) seasonal effects on functional diversity are more pronounced in rivers. Sampling was conducted between October 2018 and September 2021 in the Doce River and in shallow lakes and deep lakes of the floodplain. Functional diversity indices were measured based on seven functional traits comprising species volume, silica demand, heterocyst presence, mixotrophy potential, aerotope presence, flagella presence, and life form. Deep lakes exhibited higher functional diversity due to lower eutrophication conditions, metal contamination, and greater light availability. In the river, the increase in functional diversity during the dry season suggested an attenuation of anthropogenic pressures, considering the improvement in environmental conditions. Our results showed a dependence of the functional diversity of phytoplankton on the type of environment, and that the environments experienced distinct effects according to seasonality. Additionally, we demonstrated that resource availability, lower levels of metal contamination, and reduced grazing pressure resulted in greater functional diversity of the phytoplankton. We thus emphasize the importance of assessing functional aspects of phytoplankton in the biomonitoring of areas strongly impacted by anthropogenic activities.

Phytoplankton productivity is a key driver of ecological functioning in riverine and estuarine ecosystems. The present study assesses post-monsoon phytoplankton productivity and community structure in the lower reaches of the Kallada River, Kerala. Phytoplankton samples were collected from four stations - West Kallada, Munroe Island, Perugalam, and Koduvila - during October-February 2023. A total of about 35 phytoplankton taxa were recorded across the study area, with Bacillariophyceae forming the dominant group at all stations. Perugalam and West Kallada exhibited higher phytoplankton density and diversity, with Shannon-Wiener diversity values ranging from 2.8 to 3.3, indicating favourable conditions for sustained primary productivity. Diatom dominance ratios varied between 0.48 and 0.74, reflecting moderate to high productivity across stations, with the highest value observed at Koduvila due to dominance of Melosira varians. Munroe Island showed moderate productivity characterized by a mixed assemblage influenced by river-estuarine interactions. Cluster analysis and NMDS ordination revealed clear spatial segregation of stations based on phytoplankton composition and indicator taxa. Findings of the present study highlight pronounced spatial heterogeneity in phytoplankton-based productivity and provide baseline information for ecological assessment and management of tropical river-estuary systems.

Abstract In 70 lentic systems across Türkiye, phytoplankton communities and environmental variables were analyzed using samples collected during the spring, summer, and autumn of 2017–2019. The study aimed to assess the influence of both spatial and environmental factors on phytoplankton assemblages. The lentic systems were categorized into six ecoregions. Differences in these regions were examined in terms of environmental parameters, phytoplankton community structure, and ecological quality status. Additionally, the degree of influence of spatial and/or environmental factors on phytoplankton distribution was determined using two-way indicator species analysis (TWINSPAN), Moran's Eigenvector Maps (MEMs), Redundancy Analysis (RDA), and variation partitioning analysis. The differences observed in environmental factors across Türkiye's six ecoregions in terms of latitude and longitude are actually a reflection of various factors such as climate, geological structure, altitudinal differences, and anthropogenic effects. These differences affect phytoplankton species composition, the distribution of dominant species, phytoplankton biovolume, the ecological quality of systems, and species richness. Although TWINSPAN indicates that geographical proximity partially affects species composition distribution, MEMs and variance partitioning show that the fraction of variance uniquely explained by spatial (latitude and longitude) autocorrelation was more important for dominant species distribution. Ultimately, our findings provide compelling evidence that phytoplankton community composition is both driven by spatial factors and environmental factors, challenging overly simplistic views and reinforcing the need for multifactorial perspectives in ecological typology.

Beware of phycotoxin (okadaic acid and dinophysistoxin-1) accumulation in early post-restoration period.

Disentangling phytoplankton regime shifts and ecosystem stability under water diversion: Insights from functional traits and trophic interactions in a mesocosm experiment.

Impact of atmospheric dust on phytoplankton dynamics and primary productivity in the tropical marine ecosystem of the Eastern Arabian Sea.

Abstract The significant contribution of phytoplankton to global primary production is regulated by several abiotic and biotic factors, which are often difficult to account for in natural systems. To address these challenges, we perturbed a summer plankton community from Narragansett Bay, Rhode Island, USA, by manipulating the temperature and nutrient conditions in a controlled short‐term incubation experiment and tracked changes in phytoplankton community structure in response to fluctuations in phytoplankton physiology and microzooplankton grazing. Water was incubated at the in situ temperature (22°C) and at deviations from that temperature (± 4°C) with both macronutrient amendments (N, P, and Si addition) and unamended controls. We found nutrient availability and microzooplankton grazing to have pronounced and opposite impacts on phytoplankton size composition, with nutrient amendments shifting the phytoplankton community toward larger cells and grazing rates correlated with smaller phytoplankton communities and low‐nutrient conditions. Nutrient amendments also altered cellular elemental ratios by increasing chlorophyll : C. Conversely, temperature was not found to have a direct impact on size or elemental stoichiometry, but did influence community composition. These findings paralleled prior observations from lab and field studies in Narragansett Bay which together suggest that over shorter timescales, nutrient availability may have a greater impact on phytoplankton community composition than temperature or grazing, altering phytoplankton nutritional value for higher trophic levels and as a result, secondary production. Thus, understanding underlying nutrient dynamics will be necessary to decipher how short‐term changes in temperature or grazing may impact phytoplankton communities and the ecosystems they support.

Abstract Phytoplankton play a crucial role in regulating marine biogeochemical pathways but studying their spatial and temporal dynamics often requires extensive and laborious oceanographic expeditions. Here, we report a novel use of Biogeochemical‐Argo data to delineate planktonic habitats in the Tropical North Atlantic Ocean (TNA). We then investigated the phytoplankton biomass via in situ measurement of the BGC‐Argo floats and phytoplankton community structure of each habitat using Phytoplankton Functional Types derived from satellite observations. Our habitat delineation approach provided a finer scale and dynamic overview of phytoplankton assemblages and their surrounding environment, complementary to the widely used and static biogeochemical provinces of Longhurst. While picophytoplankton remained dominant for most communities, we found elevated abundance of microphytoplankton, including diatoms and dinophytes, and nanophytoplankton, including haptophyte and green algae, following the seasonal displacement of the Intertropical Convergence Zone, and the Amazon and Orinoco River discharges into the Tropical Atlantic and Eastern Caribbean Sea. At midlatitude, our method was able to capture both the seasonal and spatial variations of the oligotrophic region of the North Atlantic subtropical gyre. These findings shed light on the seasonality of phytoplankton distribution driven by meteorological and oceanic forcings and demonstrated the potential of the BGC‐Argo in studying and monitoring marine ecosystem.

Introduction Phytoplankton, as primary producers in aquatic ecosystems, serves as indicators of the health of water environments. In tropical island regions facing the combined pressures of human activities and climate change, understanding the mechanism underlying the phytoplankton community structure is crucial. This knowledge is essential for safeguarding drinking water sources and for identifying potential ecological risks in aquatic systems. Methods This study focused on 22 drinking water sources on Hainan Island, comprising 11 rivers and 11 reservoirs. Phytoplankton samples were collected during December 2023 (dry season) and July 2024 (wet season). We systematically analyzed the α and β diversity, explored the environmental factors influencing community changes, and examined the mechanism underlying the assembly of the phytoplankton community. Results and discussion The results revealed a clear seasonal succession in the composition of the dominant phytoplankton community. During the dry season, Cyanophyta , Chlorophyta , and Bacillariophyta were dominant, whereas in the wet season, Cyanophyta dominated. Phytoplankton α-diversity was consistently higher in rivers than in reservoirs and β-diversity was predominantly structured by species turnover (>84%). The Mantel test identified water temperature, pH and total phosphorus as key environmental factors influencing changes in the phytoplankton community structure. Co-occurrence network analysis revealed that during the wet season, the phytoplankton community nodes exhibited higher connection density and stronger correlations. The assembly of these community was primarily governed by dispersal mechanism, with niche processes playing a comparatively minor role. This study provides a novel, mechanistic framework for understanding tropical island aquatic ecosystems, offering critical insights for predicting ecological risks and guiding resilience-based water quality management in the tropical aera.

Wetlands are globally recognised as biodiversity refugia and critical climate regulators, yet they are increasingly threatened by human pressures. Although phytoplankton plays a foundational role in aquatic food webs, the ecological processes governing their community assembly, particularly the interplay between environmental filtering and dispersal limitation, remain underexplored. Here, we examine how geoenvironmental and anthropogenic drivers and dispersal processes shape phytoplankton communities across 24 small, shallow island wetlands of the Aegean archipelago (Mediterranean Sea), whose intrinsic mesocosm-like characteristics and varying degrees of human influence and biogeographic isolation provide an ideal natural experimental setup. We surveyed phytoplankton species composition and examined a suite of geoenvironmental variables (e.g. salinity, wetland area, nutrients) alongside indicators of human activities (e.g. inclusion of wetlands within protected areas, land cover, human footprint) as drivers of community assembly, using generalized linear and cumulative-link mixed-effects models. We then examined distance–decay relationships of assemblage similarity within and among islands to assess dispersal limitation. Salinity emerged as the dominant environmental filter shaping community composition. Protection status was also significant, with wetlands inside Nominally Protected Areas (NPAs) supporting assemblages distinct from those of unprotected sites. After accounting for these filters, phytoplankton similarity declined sharply with over-land distance among wetlands on the same island, indicating limited within-island dispersal. In contrast, similarity across islands remained uniformly low irrespective of distance, demonstrating that seawater imposes a strong barrier despite the theoretical capacity of phytoplankton for long-distance passive transport. Our findings support a hierarchical “triple insularity” framework, in which phytoplankton assembly is shaped by nested spatial filters: strong among-wetland environmental filtering, island-level dispersal limitation moderated by human accessibility, and cross-island isolation enforced by the sea. We propose that regionalism, typically reserved for macro-organisms, also governs phytoplankton biogeography in fragmented systems. Island wetlands occupy only a tiny fraction of global land area, yet their unique environmental gradients, limited connectivity, and growing anthropogenic pressures make them ideal natural laboratories for testing how environmental filtering, dispersal limitation, and human activity jointly shape community assembly. Environmental filtering – dominated by salinity gradients – plays a key role in structuring phytoplankton communities, while wetlands embedded in more disturbed landscapes or with weaker protection show characteristic shifts in community composition, reflecting human-mediated filtering. Community similarity declines sharply with geographic distance within islands but remains consistently low among islands, indicating strong spatial constraints on phytoplankton dispersal. Our findings provide empirical support for a “triple-insularity” model of microbial regionalism and highlight island wetlands as discrete ecological units of high conservation value.

Monitoring phytoplankton from space can help detect shifts in marine ecosystems, particularly under accelerating climate change. However, most existing ocean-colour chlorophyll-a (Chl-a) algorithms are empirical in nature, and do not explicitly consider any potential optical effects of shifts in phytoplankton community composition independent of a change in Chl-a. Similar ocean-colour signals may arise from different combinations of Chl-a and phytoplankton community composition. Revealing how phytoplankton are responding to environmental change using satellite data requires tackling this ambiguity. In previous work, we developed an Ocean Colour Modelling Framework (OCMF) to simulate ocean colour for varying Chl-a and phytoplankton size classes (PSCs). Here, we invert the OCMF to directly retrieve Chl-a, key inherent optical properties (IOPs), and PSCs, from satellite remote sensing reflectance and sea surface temperature (SST), accounting for deviations in non-algal particles (NAP) and coloured dissolved organic matter (CDOM) from assumed open ocean relationships with Chl-a. The model is validated using a global in situ dataset and shows stable performance across diverse oceanic conditions. Integrating ecological concepts into a bio-optical model may advance our ability to interpret long-term changes in phytoplankton community structure from space.

Regulation of phytoplankton community structure by nitrogen-phosphorus stoichiometry in Apostichopus japonicus culture ponds under summer high-temperature conditions

Impacts of the Yangtze-to-Huaihe water diversion project on phytoplankton community structure in Lake Caizi: Integrated effects of hydrological connectivity, water diversion, and navigation.