Distribution Of Phytoplankton Research Articles

Arctic phytoplankton microdiversity across the marginal ice zone: Subspecies vulnerability to sea-ice loss

Seasonal phytoplankton blooms are important Arctic phenomena, contributing to global primary production and biogeochemical cycling. The decline in sea-ice extent and thickness favors a longer open-water period with impacts on phytoplankton dynamics. Arctic net productivity is influenced by microalgae living associated with sea ice, with distinct species thought to be favored by ice-covered and ice-free waters. In this study, we investigated the phytoplankton community structure in Baffin Bay, a semi-enclosed sea where Arctic and North Atlantic water masses interact. We compared communities from the ice-free Atlantic-influenced eastern, the marginal ice zone, and the ice-covered Arctic-influenced western Baffin Bay. The community was characterized using 18S rRNA high-throughput amplicon sequencing and flow cytometry cell counting, and compared to environmental data collected during the Green Edge campaign. We sampled 16 stations grouped by sectors according to sea-ice cover. In the sectors associated with sea ice, phytoplankton formed a highly diverse community of smaller taxa, which contrasted with a low-diversity community in ice-free sectors, dominated by larger centric diatoms and Phaeocystis pouchetii adapted to high light/low nutrient conditions. Several phytoplankton species were flagged as indicators for the under-ice and marginal ice zone sectors, including ice-associated taxa such as the diatoms Melosira arctica and Pseudo-nitzschia seriata, but also subspecies representatives of the early-blooming alga Micromonas polaris and the cryptophyte Baffinella frigidus. The strong association of certain taxa with under-ice and marginal ice zone sectors, including Pterosperma sp., Chrysochromulina sp., Micromonas polaris, and B. frigidus, suggest that they might be indicators of diversity loss due to ongoing sea-ice changes in Baffin Bay. We report new intra-species variability of Micromonas polaris suggesting that seasonal specialists could wax and wane over the bloom and non-bloom periods, highlighting the need for detailed year-long studies and the importance of microdiversity when assessing the diversity and distribution of polar phytoplankton.

Multi-vehicle adaptive 3D mapping for targeted ocean sampling.

Expanding spatial presentation from two-dimensional profile transects to three-dimensional ocean mapping is key for a better understanding of ocean processes. Phytoplankton distributions can be highly patchy and the accurate identification of these patches with the context, variability, and uncertainty of measurements on relevant scales is difficult to achieve. Traditional sampling methods, such as plankton nets, water samplers and in-situ vertical sensors, provide a snapshot and often miss the fine-scale horizontal and temporal variability. Here, we show how two autonomous underwater vehicles measured, adapted to, and reported real-time chlorophyll a measurements, giving insights into the spatiotemporal distribution of phytoplankton biomass and patchiness. To gain the maximum available information within their sensing scope, the vehicles moved in an adaptive fashion, looking for the regions of the highest predicted chlorophyll a concentration, the greatest uncertainty, and the least possibility of collision with other underwater vehicles and ships. The vehicles collaborated by exchanging data with each other and operators via satellite, using a common segmentation of the area to maximize information exchange over the limited bandwidth of the satellite. Importantly, the use of multiple autonomous underwater vehicles reporting real-time data combined with targeted sampling can provide better match with sampling towards understanding of plankton patchiness and ocean processes.

Thermal fronts in coastal waters regulate phytoplankton blooms via acting as barriers: A case study from western Guangdong, China

Oceanic fronts play an important role in regulating the distributions of phytoplankton and are subject to climate change. However, the relationship between climate change, oceanic fronts, and coastal phytoplankton blooms requires clarification. Using long-term satellite data, the seasonal, interannual, and decadal variations of the thermal fronts were examined, along with their effects on the distribution of phytoplankton in western Guangdong. Thermal fronts between the cold western Guangdong coastal current waters and the warm South China Sea (SCS) waters were found along the coast of western Guangdong during winter due to northeast winter monsoon. At decadal timescales, an increase (decrease) in frontal activities occurred during the negative (positive) Pacific Decadal Oscillation (PDO) phase. This pattern suggests that the positive (negative) PDO activity decreases (increases) SLA and the SST in the SCS, thereby weakens (enhances) frontal activities along the coast. Accordingly, extensions and positive anomalies (>1.5 mg/m3) in Chl a were observed during the positive PDO phase, whereas Chl a was concentrated in the nearshore areas during the negative PDO phase. These processes are primarily related to the barrier effects of enhanced thermal fronts and positive SLA on offshore materials transport during the negative PDO period. This study highlights the need to incorporate PDO activity into phytoplankton production in coastal oceans.

Analysis of Chlorophyll-a Variability in the Eastern Indonesian Waters Using Sentinel-3 OLCI from 2020-2021

The Eastern Indonesian waters are significant in influencing the global climate system and oceanic connectivity. However, the Indonesian Through Flow (ITF) facilitates the movement of waters from the Pacific Ocean to the Indian Ocean. This flow vertically mixes water masses in the Eastern regions, leading to the concentration of phytoplankton. In addition, the distribution of phytoplankton, indicative of chlorophyll-a concentration, is influenced by upwelling and downwelling phenomena. Chlorophyll-a, responsible for capturing carbon and producing oxygen in marine ecosystems, is important in regulating climate change. Moreover, oceanographic conditions play a significant role in the dispersion of chlorophyll-a concentration. Therefore, this study adopted ocean colour remote sensing technology to assess chlorophyll-a distribution. Monthly ocean colour data was collected by the multi-temporal Sentinel-3 Ocean and Land Colour Instrument (OLCI). The analysis output included chlorophyll-a concentration associated with currents and the El Nino Southern Oscillation (ENSO). Data processing using the Case-2 Regional Coast Colour (C2RCC) processor resulted in an average chlorophyll-a concentration in the Eastern Indonesian waters ranging from 0.16 to 0.52. The results showed higher chlorophyll-a levels during the southeast monsoon (July to September) and lower levels during the northwest monsoon (January to March).

Quantifying the role of submesoscale Lagrangian transport features in the concentration of phytoplankton in a coastal system

Abstract Food resources in the ocean are often found in low densities, and need to be concentrated for efficient consumption. This is done in part by oceanographic features transporting and locally concentrating plankton, creating a highly patchy resource. Lagrangian approaches applied to ocean dynamics can identify these transport features, linking Lagrangian transport and spatial ecology. However, little is known about how Lagrangian approaches perform in ageostrophic coastal flows. This study evaluates two Lagrangian Coherent Structure metrics against the distribution of phytoplankton; Finite Time Lyapunov Exponents (FTLE) and Relative Particle Density (RPD). FTLE and RPD are applied to High Frequency Radar (HFR) observed surface currents within a biological hotspot, Palmer Deep Canyon Antarctica. FTLE and RPD identify different transport patterns, with RPD mapping single particle trajectories and FTLE tracking relative motion of paired particles. Simultaneous measurements of circulation and phytoplankton were gathered through the integration of vessel and autonomous glider surveys within the HFR footprint. Results show FTLE better defined phytoplankton patches compared to RPD, with the strongest associations occurring in stratified conditions, suggesting that phytoplankton congregate along FTLE ridges in coastal flows. This quantified relationship between circulation and phytoplankton patches emphasizes the role of transport in the maintenance of coastal food webs.

Distinct differences of vertical phytoplankton community structure in mainstream and a tributary bay of the Three Gorges Reservoir, China.

The vertical distribution of phytoplankton plays a crucial role in shaping the dynamics and structure of aquatic communities. In highly dynamic reservoir systems, water level fluctuations significantly affect the physiochemical conditions and the phytoplankton community. However, the specific effects on the vertical characteristics of phytoplankton between the mainstream and the tributary bay of the reservoir remain unstudied. This study investigated the vertical aspects of phytoplankton density, biomass, α and β diversity through monthly sampling over two years in the mainstream (Chang Jiang, CJ) and a tributary bay (Xiang Xi, XX) of the Three Gorges Reservoir in China. Phytoplankton density and biomass were significantly higher in XX, indicating an increased risk of algal blooms in the tributary. The phytoplankton community in CJ showed more stable species-environment relationships, a lower Shannon index and a higher evenness index, suggesting a relatively simple structure and a more uniform distribution of phytoplankton among different water layers. Conversely, XX showed greater differences between water layers (higher β diversity), with significant negative correlations with water level and positive correlations with DO difference, dissolved silica (DSi) difference, and stratification. Peak phytoplankton density and biomass, as well as high β diversity in XX, occurred during periods of decreased water levels with strong stratification in spring and summer. A structural equation model complemented by path analysis revealed that a decrease in water level could increase β diversity either directly through internal processes with extended residence time or indirectly by modifying stratification and the vertical distribution of DSi in XX. Therefore, a proposed water quality management strategy for XX was to increase the water level or reduce β diversity by implementing artificial mixing during stratification periods. Overall, this study lies in its comprehensive investigation of the vertical characteristics of the phytoplankton community in both the mainstream and the tributary bay of the Three Gorges Reservoir, elucidating the significant impact of water level fluctuations and providing insights for targeted water quality management strategies in the tributary bay to mitigate potential ecological impacts.

The utility of simulated ocean chlorophyll observations: a case study with the Chlorophyll Observation Simulator Package (version 1) in CESMv2.2

Abstract. For several decades, a suite of satellite sensors has enabled us to study the global spatiotemporal distribution of phytoplankton through remote sensing of chlorophyll. However, the satellite record has extensive missing data, partially due to cloud cover; regions characterized by the highest phytoplankton abundance are also some of the cloudiest. To quantify potential sampling biases due to missing data, we developed a satellite simulator for ocean chlorophyll in the Community Earth System Model (CESM) that mimics what a satellite would detect if it were present in the model-generated world. Our Chlorophyll Observation Simulator Package (ChlOSP) generates synthetic chlorophyll observations at model runtime. ChlOSP accounts for missing data – due to low light, sea ice, and cloud cover – and it can implement swath sampling. Here, we introduce this new tool and present a preliminary study focusing on long timescales. Results from a 50-year pre-industrial control simulation of CESM–ChlOSP suggest that missing data impact the apparent mean state and variability of chlorophyll. The simulated observations exhibit a nearly −20 % difference in global mean chlorophyll compared with the standard model output, which is the same order of magnitude as the projected change in chlorophyll by the end of the century. Additionally, missing data impact the apparent seasonal cycle of chlorophyll in subpolar regions. We highlight four potential future applications of ChlOSP: (1) refined model tuning; (2) evaluating chlorophyll-based net primary productivity (NPP) algorithms; (3) revised time to emergence of anthropogenic chlorophyll trends; and (4) a test bed for the assessment of gap-filling approaches for missing satellite chlorophyll data.

Effects of dispersal and temperature variability on phytoplankton realized temperature niches.

Phytoplankton species exhibit fundamental temperature niches that drive observed species distributions linked to realized temperature niches. A recent analysis of field observations of Prochlorococcus showed that for all ecotypes, the realized niche was, on average, colder and wider than the fundamental niche. Using a simple trait-based metacommunity model that resolves fundamental temperature niches for a range of competing phytoplankton, we ask how dispersal and local temperature variability influence species distributions and diversity, and whether these processes help explain the observed discrepancies between fundamental and realized niches for Prochlorococcus. We find that, independently, both dispersal and temperature variability increase realized temperature niche widths and local diversity. The combined effects result in high diversity and realized temperature niches that are consistently wider than fundamental temperature niches. These results have broad implications for understanding the drivers of phytoplankton biogeography as well as for refining species distribution models used to project how climate change impacts phytoplankton distributions.

A nitrogen isoscape of phytoplankton in the western North Pacific created with a marine nitrogen isotope model

The nitrogen isotopic composition (δ15N) of phytoplankton varies substantially in the ocean reflecting biogeochemical processes such as N2 fixation, denitrification, and nitrate assimilation by phytoplankton. The δ15N values of zooplankton or fish inherit the values of the phytoplankton on which they feed. Combining δ15N values of marine organisms with a map of δ15N values (i.e., a nitrogen isoscape) of phytoplankton can reveal the habitat of marine organisms. Remarkable progress has been made in reconstructing time-series of δ15N values of migratory fish from various tissues, such as otoliths, fish scales, vertebrae, and eye lenses. However, there are no accurate nitrogen isoscapes of phytoplankton due to observational heterogeneity, preventing improvement in the accuracy of estimating migratory routes using the fish δ15N values. Here we present a nitrogen isoscape of phytoplankton in the western North Pacific created with a nitrogen isotope model. The simulated phytoplankton is relatively depleted in 15N at the subtropical site (annual average δ15N value of phytoplankton of 0.6‰), where N2 fixation occurs, and at the subarctic site (2.1‰), where nitrate assimilation by phytoplankton is low due to iron limitation. The simulated phytoplankton is enriched in 15N at the Kuroshio–Oyashio transition site (3.9‰), where nitrate utilization is high, and in the region around the Bering Strait site (6.7‰), where partial nitrification and benthic denitrification occur. The simulated δ15N distributions of nitrate, phytoplankton, and particulate organic nitrogen are consistent with δ15N observations in the western North Pacific. The seamless nitrogen isoscapes created in this study can be used to improve our understanding of the habitat of marine organisms or fish migration in the western North Pacific.

Temporal and Spatial Distribution of Phytoplankton and Role of Environment Factors in the Shending River Backwater in the Danjiangkou Reservoir Area

The Danjiangkou Reservoir supplies drinking water to most residents in northern China. However, signs of eutrophication have been observed in the inlet tributaries of the reservoir, including the Shending River backwater. This research used data from the Sentinel-2 Multispectral instrument and findings from a 2021 aquatic ecological survey to analyze the spatial and temporal characteristics of phytoplankton distribution in the Shending River backwater region. The average chlorophyll a (Chl-a) concentrations by season, ranked from largest to smallest, are as follows: summer (63.96 μg/L) > autumn (41.26 μg/L) > spring (27.47 μg/L) > winter (16.21 μg/L); the upstream of the backwater area and the near-shore tributary bay had relatively higher Chl-a concentration. Bacillariophyceae (Cyclotella meneghiniana and Synedra sp.) and Cryptophyceae species (Chroomonas acuta) were dominant in spring, whereas Chlorophyceae (Scenedesmus sp. and Chlorella vulgaris) and Cyanophyceae (Dactylococcopsis acicularis, Microcystis aeruginosa and Oscillatoria tenuis) species were dominant in summer. The seasonal succession characteristics of the phytoplankton community were consistent with those of the Plankton Ecology Group model. The average phytoplankton cell density was 4.80 × 107 cells/L, and the Shannon–Wiener average diversity index was 1.95, indicating that the Shending River backwater area was moderately eutrophic. According to Pearson correlation analysis and Mantel test, the main factors causing temporal and spatial differences in phytoplankton production in the Shending River’s backwater were water level (WL), water temperature (WT), ammonia nitrogen (NH3-N) and total nitrogen (TN). In particular, WL was significantly positively correlated with Bacillariophyceae, Chlorophyceae and Cyanophyceae, whereas WT was significantly correlated with Cryptophyceae and Chlorophyceae. NH3-N and TN were significantly correlated with Cyanophyceae. Therefore, intensive nitrogen removal from the tailwater of sewage treatment plants may be considered a feasible measure to prevent cyanobacterial bloom in the Shending River backwater of the Danjiangkou Reservoir.

Phytoplankton distribution under late summer conditions in the Algerian Basin during SOMBA cruise (2014): A chemotaxonomic approach

Marine phytoplankton forms the basis of the marine food web. Its diversity (size and pigmentation) has a significant impact on biogeochemical processes such as photosynthetic efficiency, trophic interactions, and global carbon fluxes. To date, little is known about the Algerian Basin regarding phytoplankton quality and quantity. In this study, we analyzed the distribution of phytoplankton communities in the Algerian Basin based on HPLC/Chemotaxonomy analysis for the summer season of 2014. The chemical taxonomy software CHEMTAX v1.95 was used to estimate the contributions of various phytoplankton groups to total Chlorophyll a (TChla). The results showed that prymnesiophytes were the dominant group (16%) in the nanoplankton and occupied the entire water column, whereas cryptophytes were observed exclusively in the western region of the basin, and contributed about 6% to the TChla. Diatoms had the highest contributions (18%) to the TChla, and their emergence was linked to nutrient enrichment. Dinoflagellates had a contribution of about 12% with little variation throughout the basin. Prochlorococcus had a contribution of about 13% and prevailed in the deep layers (60–100 m) following the nitracline, while Synechococcus (11%) occupied the shallower layers (10–60 m) (beneath the MLD) following the nutrient depletion. Moreover, it is noteworthy that phytoplankton communities in the western part of the basin showed greater diversity and abundance, influenced by Atlantic waters and deep nutrient enrichment. In contrast, the eastern part of the basin displayed lower productivity, characterized by reduced diversity and the prevalence of nano- and picoplankton.

Exploring the mesoscale connectivity of phytoplankton periodic assemblages' succession in northern Adriatic pelagic habitats

An appropriate model for phytoplankton distribution patterns is critical for understanding biogeochemical cycles and trophic interactions in the oceans and seas. Because phytoplankton dynamics in coastal waters are more complex due to shallow depth and proximity to land, more accurate models applied to the correct spatial and temporal scales are needed. Our study investigates the role of the atmosphere and hydrosphere in pelagic habitat by modelling phytoplankton assemblages at two Long Term Ecological Research sites in the northern Adriatic Sea using niche-forming environmental variables (wind, temperature, salinity, river discharge, rain, and water column stratification). To study the synchronization between the phytoplankton community and these environmental variables at the two LTER sites, we applied current linear and nonlinear numerical methods for ecological modelling. The aim was to use periodic and/or non-periodic properties of the environmental variables to classify the phytoplankton assemblages at one LTER site (Gulf of Trieste - Slovenia) and then predict them at another LTER site 100 km away (Gulf of Venice - Italy). We found that periodicity played a role in the explanatory and predictive power of the environmental variables and that it was more important than non-periodic events in defining the common structure of the two pelagic habitats. The non-linear classification functions of the neural networks further increased the predictive power of these variables. We observed partial synchronization of communities at the mesoscale and differences between the original and predicted assemblages under similar environmental conditions. We conclude that mesoscale connectivity plays an important role in phytoplankton communities in the northern Adriatic. However, the loss of periodicity of niche-forming variables due to more frequent extreme meteorological and hydrological events could loosen these connections and affect the temporal succession of phytoplankton assemblages.

Study of Water Quality and Distribution of Phytoplankton in Hebbal Lake, Krishnarajanagara

Abstract: Life on earth depends on fresh water. Phytoplanktons are free floating, photosynthetic, aquatic microorganisms, which moves from one place to another. Phytoplanktons which are present in Hebbal Lake, Krishnarajanagara, and Mysore were studied with respect to their species diversity and distribution. The phytoplankton community is mainly represented by algal representatives including both prokaryotes and eukaryotic genera. Studies on phytoplankton and water quality of Hebbal Lake, Krishnarajanagar, Mysore Karnataka were undertaken for 5months from May 2023 to September 2023. The quantitative analysis of phytoplankton was done by Lackey’s drop method modified by saxena (1987).Diversity indices have been discussed by using PASTA Software Program. Physical and Chemical parameters were analysed using the standard methods of APHA (2025) and Trivedi and Gael (1984). Among the total 60 species recorded, 33species of Bacillariophyceae, 7species of Chlorophyceae, 8species of Cyanophyceae, 8 species of Desmidiaceae, 3species of Euglenophyceae are reported. Bacillariophyceae was the most dominant group followed by Chlorophyceae, Cyanophyceae, Desmidiaceae and Euglenophyceae. The result of physicochemical and biological parameters along with statistical method and biodiversity indices indicated that the Hebbal Lake is threatened ecologically due to various anthropogenic activities which lead organic pollution and eutrophication status of the lake. Statistical program Bray – Curtis similarity index explained, the cluster of EC, Total hardness and Total alkalinity is highly correlated with the clusters of phytoplanktons. Shannon and Weiner index showed that the lake was heavily polluted in the month of May due to increased temperature.

Comparative analysis of phytoplankton dynamics and water quality assessment in selected lentic water bodies of Haryana, India

The study was designed to assess the water quality based on physico-chemical parameters and phytoplankton communities of eight lentic water bodies of Haryana which are famous for mass bathing and religious rituals taking place here. To evaluate comparative analysis of composition, diversity and distribution of Phytoplankton and physico-chemical factors, water samples were collected seasonally viz., summer, monsoon, post monsoon and in winters from all the eight sites in triplicate. Total 118 phytoplankton taxa were observed at all sites. Among these cyanophyceae group was found most dominant at sites 1, 2, 4, 5, 7, 8 whereas cholorophyceae at site 6, bacillariophyceae at site 1,3,4,7 whereas xanthophyceae was in abundance at site 5. Population density (nos. L-1) wise phytoplankton trend was Cyanophyceae > Chlorophyceae > Bacillariophyceae >Desmidiaceae and Species diversity wise phytoplankton trend observed was Chlorophyceae > Bacillariophyceae > Cyanophyceae >Desmidiaceae. Correlation of different phytoplankton groups with physicochemical factors revealed a significant negative correlation of Cyanophyceae with pH, whereas a significant positive correlation of ortho-phosphate with Desmids and bacillariophyceae wheareas CO2 showed a positive correlation with Xanthophyceae.  Appearance of pollution tolerant taxa of phytoplankton Microcystis aeruginosa, Phormidium sp., Scenedesmus spp., Pediastrum spp., Mougeotia sp., Synedra sp., Pediastrum spp. at most of the sites indicated the sign of the more organic pollution and degradation in the water quality of the selected sites due to religious immersion, mass bathing and by other anthropogenic activities. Suitable remedial actions should be adopted by regulatory bodies and policy makers to maintain the water quality of these aquatic systems.

Conventional net tow versus environmental DNA for metabarcoding-based analysis of plankton-environment interactions in polluted aquatic ecosystems

Human societal development has caused rapid degradation of freshwater ecosystems, resulting in significant biodiversity decline globally. The conservation of aquatic ecosystems, particularly the management of biodiversity in urban areas, has become an increasingly significant issue for ensuring the sustainability of these ecosystems. The restoration of degraded aquatic ecosystems relies on a comprehensive understanding of the interactions between biological communities and multiple stressors derived from human activities. Environmental DNA (eDNA)-based methods have emerged as effective tools for dissecting complex community-environment interactions. Nevertheless, potential causes for technical disparities and conclusions drawn from conventional sampling versus eDNA-based methods remain inadequately evaluated. In this study, we conducted a comprehensive survey of plankton communities along the environmental gradient of the North Canal River in Northern China to assess causes and consequences for any disparities between conventional plankton net tow and eDNA sampling for metabarcoding-based analysis of plankton-environment interactions. Our findings demonstrated that eDNA-metabarcoding was effective for characterizing both biodiversity and geographical distribution. Both methods exhibited general consistency in elucidating community structure and identifying the key environmental factors influencing geographical distribution of both zooplankton and phytoplankton. As we explored lower taxonomic ranks, we found inconsistent patterns at certain levels (e.g., phylum or order) within some taxa (e.g., Bacillariophyta and Rotifera), even substantial variability for several taxonomic groups (e.g., Euglenozoa and Apicomplexa). The varied environmental prevalence and persistence of eDNA, biological and ecological characteristics of diverse taxa in plankton, and sampling efficiency of both methods likely contributed to the observed disparities. Given its higher biodiversity recovery capacity, efficiency, sampling convenience, and capability to identify influential factors driving the geographical distribution of biodiversity, eDNA-based metabarcoding is recommended for studying plankton-environment interactions, particularly in studies involving a large number of samples at extended geographical scales.

Monitoring the distribution of phytoplankton in vannamei shrimp cultivation in intensive system, Banyuwangi, East Java, Indonesia

The increase in Vannamei shrimp farming is closely related to an increase in the demand for shrimp feed. At present there are many technological developments in cultivating natural feed. The natural feed here refers to plankton which can be used as natural food for every organism of larvae in waters. Conditions in water will affect the distribution pattern of phytoplankton either horizontally or vertically. As a result, it affects the abundance of phytoplankton and subsequently also affects the value of the main productivity. The purpose of study is to find out the cultivation process and to find out the types of plankton that exist in Vannamei shrimp farming ponds. Plankton observations were carried out directly with the help of a microscope and haemocytometer, while the measurement of water quality using each instrument had been prepared for each parameter. The results of plankton observations found species of Chaetoceros sp., Oocystis sp., Oscillatoria sp. and Cyclotella sp. while the water quality measurements obtained temperature (29-31°C); DO during the day (7.6-9.5 ppm) and at night (4.0-4.6 ppm); pH in the morning (7.8-8, 5) and daylight (8.1-9.0); and salinity 26-27 ppt. The application of probiotics used carbon sources derived from molasses and katul.

Tidal Variability of Phytoplankton Distribution in the Highly Turbid Changjiang River Estuary: Mechanisms and Implications

AbstractPhytoplankton distribution in macrotidal estuaries varies strongly due to highly dynamic conditions, contributing to the complexity of aquatic environments and marine ecosystems. Here the Changjiang River Estuary was analyzed as an example to explore this issue, based on field data collected through multiple cruises (including one covering a complete spring‐neap tidal cycle) and a fully coupled hydrodynamics‐sediment‐ecosystem numerical model. The composite analysis of all cruise data clearly showed that the chlorophyll concentrations were relatively low on lunar days 14–17 and 28–2, which corresponded to spring tides. Mechanistic analysis indicated that during spring tides, the river plume front retracts upstream with enhanced vertical mixing. This process restricts the transport of fluvial nutrients while increasing sediment resuspension, and therefore inhibiting net phytoplankton growth. During non‐spring tides, sediment resuspension was reduced but the river plume was further extended with slowed tidal currents, which enhanced the onshore light availability and offshore nutrient conditions and hence stimulated phytoplankton blooms in a larger area. The onshore shifting trend of the chlorophyll maximum region could last till the following neap tide with improved onshore light conditions and activate more conservative nutrients. The non‐conservation of nutrients augments the uncertainty of biomass variations during non‐spring periods. Besides in the spring‐neap tidal cycle, the phytoplankton variability between the perigean and apogean spring tides was also revealed. This study contributes to an improved understanding of intertidal variations of phytoplankton bloom and underlying physical‐sedimentological‐biological coupling mechanisms in tidal estuaries.

Seasonal variation in plankton abundance and diversity of Tanga coastal waters, Tanzania

Several studies have reported on seasonal patterns in plankton (phytoplankton and zooplankton), in different ecoregions. However, information on these plankton along the coastal waters of Tanga is limited. This study attempts to uncover and describe information related to abundance, distribution, and diversity of phytoplankton and zooplankton in the coastal waters located in the western side of the Pemba Channel, Tanzania, during the southeast monsoon (SEM) and the northeast monsoon (NEM) seasons. The samples of phytoplankton, zooplankton and environmental variables were collected in the coastal waters of Tanga, from June 2019 to January 2021. A total of 199 species of phytoplankton and 32 genera of zooplankton were identified. Although the abundance varied between the SEM and the NEM seasons, Bacillariophyceae were the most abundant among the phytoplankton groups, while Copepods were the most abundant zooplankton in both seasons. The abundance variation in phytoplankton and zooplankton could be attributed to environmental variables, which varied significantly between seasons. The results suggest that high nutrients concentration during the SEM season influences high plankton abundance, richness, and diversity.

Concentration phenomenon of single phytoplankton species with changing-sign advection term

In this paper, a nonlocal reaction-diffusion equation modeling the growth of phytoplankton species with changing-sign advection in a vertical water column is investigated, where the species depends solely on light for its metabolism. We mainly study the concentration phenomenon of the phytoplankton with large advection amplitude and small diffusion rate. Firstly, we study the threshold-type dynamics of the population by critical death rate d⁎. Secondly, we examine the concentration phenomenon with large advection amplitude and small diffusion in two cases: (i) the advection function h(x) changes sign only once from positive to negative in water column [0,1]. We find that the phytoplankton will concentrate at certain critical point with large advection amplitude and small diffusion; (ii) the advection function h(x)<0 in [0,κ) with ∫0xh(s)a(s)ds<0 for all x∈(0,1], the phytoplankton will concentrate at the surface of water column with large advection amplitude and small diffusion. We also investigate the limiting distribution of phytoplankton as diffusion rate D→+∞: the phytoplankton tends to even distribution in water column.

Impact of surface and subsurface-intensified eddies on sea surface temperature and chlorophyll a in the northern Indian Ocean utilizing deep learning

Abstract. Mesoscale eddies, including surface-intensified eddies (SEs) and subsurface-intensified eddies (SSEs), significantly influence phytoplankton distribution in the ocean. Nevertheless, due to the sparse in situ data, understanding of the characteristics of SSEs and their influence on chlorophyll a (Chl a) concentration is still unclear. Consequently, the study utilized a deep learning model to extract SEs and SSEs in the northern Indian Ocean (NIO) from 2000 to 2015, using satellite-derived sea surface height (SSH) and sea surface temperature (SST) data. The analysis revealed that SSEs accounted for 39 % of the total eddies in the NIO, and their SST signatures exhibited opposite behaviour compared to SEs. Furthermore, by integrating ocean colour remote-sensing data, the study investigated the contrasting impacts of SEs and SSEs on Chl a concentration in two basins of the NIO, the Arabian Sea (AS) and the Bay of Bengal (BoB), known for their disparate biological productivity. In the AS, SEs induced Chl a anomalies that were 2 to 3 times higher than those caused by SSEs. Notably, there were no significant differences in Chl a anomalies induced by the same type of eddies between summer and winter. In contrast, the BoB exhibited distinct seasonal variations, where SEs induced slightly higher Chl a anomalies than SSEs during the summer, while substantial differences were observed during the winter. Specifically, subsurface-intensified anticyclonic eddies (SSAEs) led to positive Chl a anomalies, contrasting the negative anomalies induced by surface-intensified anticyclonic eddies (SAEs) with comparable magnitudes. Moreover, while both subsurface-intensified cyclonic eddies (SSCEs) and surface-intensified cyclonic eddies (SCEs) resulted in positive Chl a anomalies during winter in the BoB, the magnitude of SSCEs was only one-third of that induced by SCEs. Besides, subsurface Chl a induced by SSAEs (SSCEs) is ∼0.1 mg m−3 greater (less) than that caused by SAEs (SCEs) in the upper 30 (50) m using Biogeochemical Argo profiles. The distinct Chl a between SEs and SSEs can be attributed to their contrasting subsurface structures revealed by Argo profiles. Compared to SAEs (SCEs), SSAEs (SSCEs) enhance (decrease) production via the convex (concave) of the isopycnals that occur around the mixed layer. The study provides a valuable approach to investigating subsurface eddies and contributes to a comprehensive understanding of their influence on chlorophyll concentration.