Phytoplankton Biomass Research Articles

Water level fluctuations shape phytoplankton community in the Xiangxi Bay from Three Gorges Reservoir.

Dissolved organic phosphorus utilization and composition under different water regimes of a river-dominated estuary.

Unprecedented high-temperature triggers a rapid shift in ecological characteristics of phytoplankton succession in the southern coastal waters of Korea.

Seasonal dynamics at low trophic level and ecological interactions of microbial and plankton communities during harmful algal blooms.

Studying the biocenoses of urban reservoirs can signifi cantly expand the understanding of the biodiversityof specially protected natural territories located within the city. In 2024, the phytoplankton of reservoirs of theStarozagorodny natural recreational complex of regional importance, located in the center of Omsk, was studied for thefi rst time. Two artifi cial fl owing reservoirs (small and large) have the established nature protection regime, the main taskof which is to regulate anthropogenic load. Th e study determined the taxonomic composition, abundance and biomassof phytoplankton, and established the trophic status of water bodies. Th ree new species and intraspecifi c taxa of algaefrom the Chlorophyta (1 BBT) and Charophyta (2 BBT) divisions have been identifi ed in the phytoplankton of reservoirs.Information is also provided on green and desmidium algae found in reservoirs rare for the IWT region. Micrographs ofnew and rare species are presented, as well as a brief description with instructions. In terms of biomass, the trophic statusof the large reservoir corresponded to the eutrophic category of waters, and that of the small reservoir corresponded to themesotrophic category. Th e conducted studies allowed us to supplement the taxonomic list of algae and cyanobacteria ofthe Omsk Irtysh region, which currently includes 1166 IWT.

To elaborate on the effects of hydraulic projects and physicochemical factors on the spatiotemporal distribution of phytoplankton communities, we monitored the phytoplankton communities and related water parameters in the Ganjiang River’s main channel over a five-year period. The survey revealed 65 species across six phyla, with Chlorophyta, Cyanophyta and Bacillariophyta as the most diverse groups. Phytoplankton abundance and biomass exhibited significant seasonal variations (p < 0.001), peaking in summer and autumn and reaching their lowest values in winter and spring. Spatially, phytoplankton abundance and biomass were not significantly different (p > 0.05), the abundance and biomass of Cyanophyta were higher in the two reservoir areas compared to the upstream sampling points. This suggests that the hydraulic projects altered the river’s flow and velocity, which led to a succession in phytoplankton community composition. Correlation analysis showed a strong positive association between the abundance and biomass of both Cyanophyta and Chlorophyta and water temperature (p < 0.001), but showed a significant negative relationship with nitrogen (p < 0.05). In contrast, Bacillariophyta abundance and biomass were positively and significantly correlated with ammonium nitrogen (p < 0.05). Redundancy analysis confirmed that water temperature and nitrogen are the primary environmental variables influencing the phytoplankton community’s succession. The direct alteration of river hydrodynamic characteristics by hydraulic projects, coupled with the reservoir-induced water stratification and its influence on vertical water temperature distribution, ultimately results in the profound reshaping of the phytoplankton community structure through coupled effects with nitrogen cycling. The findings from this study can scientifically inform the ecological scheduling, water quality management and water supply security of the Ganjiang River basin’s cascade reservoirs.

Abstract Typhoons typically enhance phytoplankton biomass in the upper ocean, as evidenced by elevated sea surface chlorophyll ‐a concentrations (Chl‐ a ). However, subsurface Chl ‐a responses remain debated, leading to uncertainty about whether vertically integrated Chl ‐a over upper depth increases or decreases. Using a coupled physical‐biogeochemical model, this study reveals that the depth‐averaged Chl ‐a response to a typhoon exhibits distinct spatial patterns relative to the storm's track. Near the typhoon's path, intense vertical mixing penetrates beyond the nutricline, transporting deep nutrients into the upper ocean. The supplied nutrients fuel phytoplankton growth in both surface and subsurface layers, thereby increasing depth‐averaged Chl‐ a over upper 150 m. However, the increase in subsurface Chl ‐a driven by biogeochemical processes is smaller than the decrease caused by physical processes, resulting in a net reduction of Chl ‐a in the subsurface layer. This ultimately leads to a significant increase in the surface layer, a minor decrease in the subsurface layer, and an overall rise in total Chl‐ a concentration. In contrast, areas farther from the track experience mixing that exceeds the mixed layer depth but remains shallower than the nutricline. Here, mixing redistributes subsurface Chl ‐a to the surface without uplifting new nutrients. Consequently, surface Chl ‐a rises, while subsurface levels decline, leaving the depth‐averaged Chl ‐a largely unchanged. These spatially divergent responses explain why observed vertical Chl ‐a profiles vary across different cross‐track locations. Clarifying the spatial variability of upper ocean Chl ‐a dynamics under typhoon forcing is critical for accurately assessing typhoons' ecological impacts, including their role in marine carbon cycling and productivity.

ABSTRACT Phytoplankton underpin marine food webs and carbon cycling, converting dissolved carbon dioxide into organic matter and exporting it to deeper layers. However, these organisms are sensitive to environmental changes that affect their growth and community structure differently, which may be represented by their taxonomic structure or cell size categories. Consequently, there is increasing interest in developing and improving satellite-based models for estimating the abundance of phytoplankton size classes (PSCs) and different taxonomic groups. Satellites can reliably estimate two key properties related to phytoplankton biomass and ocean dynamics: chlorophyll-a concentration (Chla), the primary pigment of phytoplankton, and sea surface temperature (SST), which is associated with water masses and often related to nutrient availability. In this study, we tested different approaches and developed regional models to retrieve PSCs from satellite data. The regional models were fitted to the South Brazil Bight (SBB) in the Southwestern Atlantic Ocean. The in situ training and validation datasets were obtained from oceanographic cruises conducted in the SBB during 2019–2022. We applied different model parameterisation schemes to compare SST-independent and SST-dependent models with both global and regional fits. The models were applied to both in situ data and satellite observations from Ocean and Land Colour Instrument (OLCI) sensors on board Sentinel 3A and 3B satellites, alongside the Multi-scale Ultra-high Resolution (MUR) SST product. The regional SST-dependent approach consistently outperformed alternatives across all size classes, achieving correlation coefficients (ρ) greater than 0.7, bias less than 0.14, and mean absolute error (MAE) of less than 0.36. By comparison, the regional SST-independent approach (ρ > 0.54, bias < 0.17, MAE < 0.38) and the global SST-dependent approach (ρ > 0.59, bias < 0.11, and MAE < 0.40) showed weaker performance. These results highlight the importance of regional SST-dependent models for improving PSC estimation accuracy in the SBB and similar regions where SST variability affects nutrient availability, phytoplankton biomass, and community structure.

Poyang Lake, China’s largest freshwater lake, is an ecologically significant but increasingly vulnerable system threatened by eutrophication and harmful algal blooms driven by human activities. Phytoplankton organisms, as primary producers and sensitive bioindicators, provide critical insights into these ecological changes; however, comprehensive seasonal assessments remain scarce. This study examined intra-annual phytoplankton dynamics at 15 representative sites, with the objectives of quantifying seasonal and spatial variations in community composition, density, biomass, and diversity, and identifying key environmental drivers. Surface water samples were collected during four seasons. Phytoplankton were identified microscopically, and diversity was quantified using Shannon–Wiener, Pielou’s evenness, and Margalef’s richness indices. Concurrent measurements included water temperature (WT), dissolved oxygen (DO), nutrients (TN, TP, NO3−-N, NO2−-N, NH4+-N), chemical oxygen demand (COD), pH, and transparency. Pearson correlation and redundancy analysis (RDA) were applied to evaluate phytoplankton–environment relationships. A total of 118 phytoplankton species belonging to 7 phyla were identified. Chlorophyta, Cyanobacteria, and Bacillariophyta exhibited the highest species richness. The highest seasonal abundances were observed for Microcystis wesenbergii (0.998) in winter, Aulacoseira granulata var. angustissima (0.780) in spring, and Snowella lacustris (0.520) in autumn, indicating pronounced seasonal shifts in dominant taxa across Poyang Lake. Phytoplankton density and biomass peaked in summer, while diversity indices significantly declined with increasing WT. RDA revealed that WT, DO, TP, and transparency collectively explained 45.7% of the community variation, with DO emerging as the most influential factor. These findings demonstrate that physical drivers, particularly thermal conditions and oxygen availability, exert stronger influences on phytoplankton diversity than nutrients alone, challenging nutrient-centric paradigms. Management should integrate hydrological and oxygen regulation with nutrient control, while long-term monitoring, depth-stratified sampling, and trait-based approaches are recommended to improve predictive models under climate variability.

Abstract Exploring the response of phytoplankton composition and diversity to water travel time (WTT) in rivers is crucial for understanding the biogeographic patterns of these organisms and for protecting watershed ecosystems. This study investigated the effects of WTT on phytoplankton biomass, community composition, and diversity by analyzing 182 samples collected over two seasons from the mainstems and tributaries of the Hanjiang and Danjiang River basins, China. Our study found that, in free‐flowing river reaches, phytoplankton biomass fluctuated and increased progressively from the headwaters to downstream areas along the river flow. Water travel time was the key factor driving phytoplankton biomass and diversity rather than water quality. As WTT increased, phytoplankton biomass, the proportion of Cyanophyta, and the theoretical maximum number of genera (N) increased, while the critical percentage of taxon extinction (a) and the evenness of the taxon distribution (k) decreased. In comparison, the Shannon index showed no distinct pattern of changes. In cascade dam‐controlled river reaches, dams and tributaries disrupted the longitudinal continuity of rivers. Both dam barriers and tributary inflow reduced the contribution rate of upstream phytoplankton communities to downstream reaches. Additionally, dams reduced downstream phytoplankton biomass by altering flow conditions, shifting the dominant control to water quality for phytoplankton community composition and diversity indices. In autumn, increased tributary flow into the mainstem reduced the contribution of upstream phytoplankton communities to downstream areas through a dilution effect. Overall, WTT plays a pivotal role in shaping the biogeography of phytoplankton, while cascade dams and tributaries disrupt the natural riverine longitudinal patterns.

Although phosphorus (P) has been the primary focus of lake eutrophication management efforts globally, we show that reducing nitrogen (N) inputs to shallow P-rich lakes can rapidly reverse accelerated eutrophication. We conducted a long-term field mesocosm manipulation experiment testing the effects of variable N and P stoichiometry on the eutrophication of lakes, particularly the comparative productivity of lakes with low N:P inputs versus high N:P inputs and the subsequent effects of reducing N inputs while maintaining P inputs. Nitrogen enrichment in excess of balanced N:P ratios (20-50 molar) resulted in phytoplankton biomass well above thresholds indicative of healthy lake ecosystems. After 4 years of both N and P enrichment, we eliminated N fertilization while maintaining P fertilization and observed a 57 ± 3.1% reduction in phytoplankton biomass across all fertilization treatments. Comparative analysis of our experimental results with the 2022 U.S. National Lakes Assessment suggested that excess N is contributing to eutrophication for approximately 40% of U.S. lakes. Despite the capacity of lake ecosystems to import N from N fixation, reducing N inputs to shallow P-rich lakes has the potential to decrease phytoplankton biomass and the harmful effects of accelerated eutrophication.

The coastal Oder/Szczecin Lagoon is subject to multiple external changes, particularly the reduction in external nutrient loads and the impacts of climate change, including rising temperatures and more frequent heatwaves. By combining monitoring data covering the past 40 years with 3D ecosystem modelling, we assess changes in phytoplankton abundance and diversity across different temporal scales, ranging from long-term trends to the short-term effects. Despite strong reductions in external nutrient loads, neither the average annual phytoplankton biomass nor the long-term species composition changed significantly, although extreme summer blooms appear to have decreased. In summer, cyanobacteria, usually dominated by Microcystis, can reach a relative biovolume of up to 90%. Bacillariophyceae (diatoms) contribute up to 72% of the annual relative biovolume and dominate in spring. Both interannual and short-term variability in phytoplankton biomass and composition are pronounced. Heat- and coldwaves show no consistent immediate effects; however, results suggest that cyanobacteria, particularly Microcystis, benefit from hot summers. In contrast, diatoms appear less responsive to temperature, although they tend to contribute more in colder years, with distinct shifts in species composition observed between hot and cold springs. Model simulations indicate that a 1.5 °C increase in air temperature would, via elevated water temperatures, raise average monthly phytoplankton biomass by 4% in July and by 9% in August, further promoting cyanobacteria growth.

In this paper, the applicability of chlorophyll fluorescence for analyzing changes in phytoplankton biomass following the passage of a cyclone named Mandous has been investigated using Sentinel-3 Ocean and Land Color Imager (OLCI) data. OLCI daily Level 2 reflectance data from 2–20 December 2022 was processed for the Fluorescence line height (FLH) estimation, to analyze the pre and post-cyclone fluorescence. It was observed that the chlorophyll concentration increased by up to 10 times after the passage of the cyclone Mandous, and a bloom-like feature extended from 9-140N and 81-850E. Before the cyclone, chlorophyll concentration in the Bay of Bengal was low, with chlorophyll concentration ranging between 0.2–0.5 mg/m3, which increased to 2–3 mg/m3 on 16 December. FLH product computed from the normalized water-leaving radiance showed an increase in the chlorophyll fluorescence beginning from 12 December, and continuing up to 20 December. Finally, a new algorithm for chlorophyll inversion in case-2 waters and bloom regions is presented by developing a regression relationship between FLH and chlorophyll. This alternate chlorophyll algorithm has been tested in coastal and estuarine waters of Goa, India and are found to perform significantly better than empirical OC4 based algorithm and neural network based algorithm of OLCI.

During the 84th cruise of the R/V Akademik Mstislav Keldysh in August 2021, patterns of phytoplankton composition transformation were revealed along a northward gradient. The study involved three transects in the Fram Strait and adjacent Arctic waters: a southern transect (from the Barents Sea shelf to the Greenland shelf), a middle transect across the Fram Strait, and a northern transect along the ice edge. Ten species of diatoms and eleven of dinoflagellates were identified, and their ecological preferences were characterized by determining the minimum, maximum, mean, and median values for abundance, biomass, depth of the biomass maximum, salinity, temperature, and the concentrations and ratios of nitrogen, phosphorus, and silicon. Significant gradients in temperature, salinity, silicon, and nitrogen concentrations were recorded along the south–north direction in the study area. The phytoplankton community responds to these changing factors through restructuring. Dinoflagellates predominantly dominate the southern and middle transects, whereas large diatoms make a substantial contribution to the phytoplankton biomass in the northern transect. Diatom biomass is determined by nitrogen concentration. The dependence of dinoflagellate biomass on that of small flagellates confirms the importance of mixotrophic nutrition. A hypothesis is proposed that the most probable criterion for the selective selection of diatoms northward is the half-saturation constant for nitrogen uptake, while for dinoflagellates, it is temperature.

Abstract Over the past decades, improvements in water quality—particularly increased oxygen and reduced nitrogen concentrations—have led to changes in phytoplankton biomass and community composition in the Schelde estuary, a macrotidal estuary in Belgium/SW Netherlands. We argue that these changes have affected SPM dynamics by modifying floc stability and size. Seasonal and spatial variability in SPM flocculation dynamics were examined using water samples collected monthly from December 2021 to December 2022 at five stations in the freshwater and brackish tidal reaches of the estuary. In a custom‐built flocculation chamber, these samples were first subjected to a high turbulent shear rate (45 s−1) to break the flocs, followed by a lower shear rate (20 s−1) that promoted aggregation for 120 min. Floc size distribution changes were analyzed to determine key flocculation parameters, in particular, equilibrium floc size (De), and flocculation speed (Vf). Using generalized additive models, we assessed the influence of seasonal, spatial, environmental, and biotic factors on De and Vf. Unlike in the brackish stations, the freshwater stations displayed clear seasonal patterns in flocculation dynamics, with De and Vf increasing in spring and summer. The strong positive correlations between De, Vf, and Chl a, as well as between Vf and phytoplankton‐derived particulate organic carbon, suggest that phytoplankton plays a key role in the flocculation process. Transparent exopolymer particles (TEP), which because of their sticky properties can promote particle coagulation, were only weakly correlated with enhanced flocculation, suggesting that TEP properties may be affected by factors such as its specific composition, age, and remineralization.

Abstract Mesopelagic fish constitute the most abundant vertebrate group in the marine environment. Mueller’s pearlside (Maurolicus muelleri) is present in the twilight zone across the Atlantic Ocean, including the Mediterranean; however, little is known about its distribution patterns and environmental preferences. Based on acoustic and biological sampling, we demonstrate that M. muelleri predominantly forms monospecific aggregations with characteristic echotraces. An ensemble of Species Distribution Models (SDMs) was applied, paired with satellite-derived environmental observations and model outputs to explore the potential habitat of the species in the Eastern Mediterranean Sea. Bottom depth showed the highest variable importance in all models, followed by surface chlorophyll-a concentrations (an index of phytoplankton biomass) and current geostrophic velocity. Extended areas of high probability of presence were identified near the shelf breaks throughout all sub-basins, in the zone of 150-250 m. M. muelleri is more likely to occur in productive regions than in oligotrophic ones, suggesting that ongoing Mediterranean ocean warming—which reduces primary productivity—may indirectly affect the species’ abundance by limiting food availability. Inter-model variability indicated low uncertainty, which was attributed to the species’ strong dependence on a narrow range of only a few environmental variables. The findings contribute to our understanding of the spatial distribution of a key mesopelagic fish in the Eastern Mediterranean Sea and its association with topographic and environmental drivers.

Human activities and climate override local catchment characteristics in explaining long-term phytoplankton trends in prairie lakes.

Reproductive dynamics of the sea cucumber Holothuria arguinensis: Biological insights to support fisheries management.

The effects of diluted bitumen, the shoreline washing agent Corexit EC9580A, and bio-stimulation on the lower food web of a boreal lake.

Abstract Mediterranean coastal lagoons are increasingly affected by nutrient enrichment from both natural and anthropogenic sources. While most studies focus on total nutrient loads, little is known about how the mode of nutrient delivery, pulsed or continuous, affects plankton community dynamics. This study aimed to experimentally test how different nutrient input regimes influence zooplankton community structure and plankton biomass under microcosm conditions using natural lagoon water. Three nutrient regimes were applied: Pulse (P), Continuous (C), and Pulse–Continuous (PC), along with a Control (no addition), with total nutrient concentrations standardized across regimes. Biomass of bacterioplankton, phytoplankton, and zooplankton, as well as hydrochemical variables and species composition, were monitored over 28 days. P regimes led to reduced zooplankton biomass and impaired reproduction, while C and PC regimes maintained higher productivity and favored shifts in rotifer and copepod composition. To evaluate community response, we used the Z 2 index, a disturbance metric developed for Mediterranean lagoons that quantifies the severity of environmental disturbance based on zooplankton assemblages. Z 2 scores revealed a gradient aligned with nutrient delivery mode, with small but consistent increases in C and PC regimes. These findings highlight the potential long-term impacts of continuous low-level nutrient inputs in restructuring aquatic communities.