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Thermal stratification has become more extensive and prolonged because of global warming, and this change has had a significant impact on the distribution patterns of the phytoplankton communities. However, the response of phytoplankton community structures and assembly processes to thermal stratification is not fully understood. We predicted that the structure and assembly processes of phytoplankton communities would be affected by thermal stratification among water layers associated with environmental condition changes, reflecting certain patterns in temporal and spatial scales. Phytoplankton from Danjiangkou Reservoir were collected from October 2021 to July 2022 to verify this prediction. During the sampling period, Danjiangkou Reservoir remained thermally stratified with stability. The composition of the phytoplankton community in the surface layer significantly differed from that in both the thermocline and bottom layer. The phenomenon of thermal stratification affected the pattern of nitrogen and phosphorus distribution and, thus, the processes of the phytoplankton community structures. Deterministic processes had a greater influence on the assembly of the phytoplankton communities in the surface and bottom layers. In contrast, stochastic processes were more prevalent in the assembly of the thermocline phytoplankton community. The phytoplankton community within the thermocline layer exhibited a broader niche range than that in the surface and bottom layers, showing notable dissimilarity from that of the bottom layer. Canonical correspondence analysis (CCA) revealed that the vertical distributions of the phytoplankton communities were significantly correlated with NH4+-N, pH, and water temperature (WT). In summary, this study explained the distribution patterns of phytoplankton community structures and assembly processes in deep-water reservoirs during the stratification period. Additionally, the study explored the potential of using the distribution patterns of phytoplankton in stratified-state deep-water reservoirs under a subtropical–warm temperate climate as climate indicators in the context of global warming. [ABSTRACT FROM AUTHOR]

Understanding the future of Southern Ocean ecosystems requires approaches at micro to macro scales. The Southern Ocean has experienced both top-down and bottom-up perturbations driven by man. The removal of whales and finfish was a top-down disruption, removing enormous levels of biomass of consumers and driving competitive release for other predators. In contrast, climate change is altering physical conditions in complex, interrelated ways likely to change primary-producer community structure, with bottom-up consequences for the efficiency of energy transfer to top predators, and for the biological pump. The physiological effects of increasing ocean temperatures on animal species are likely to be less important than three key physical changes: loss of sea ice, changes to water-column stability, and patterns of water transport; these will affect krill abundances, primary producer community structure, and prey availability to land-breeding predators, respectively. The Southern Ocean is vast and critically influenced by global teleconnections, with different regions already exhibiting different patterns of physical and biological change. Given the strong physical forcing of these ecosystems, many of the initial consequences of climate change will operate through direct physiological effects on the primary producers and indirect effects on the larger organisms. This will disrupt species interactions and drive new ecological relationships. [ABSTRACT FROM AUTHOR]

Marine phytoplankton in the northern Benguela upwelling system (nBUS) serve as a food and energy source fuelling marine food webs at higher trophic levels and thereby support a lucrative fisheries industry that sustain local economies in Namibia. Microscopic and chemotaxonomic analyses are among the most commonly used techniques for routine phytoplankton community analysis and monitoring. However, traditional in situ sampling methods have a limited spatiotemporal coverage. Satellite observations far surpass traditional discrete ocean sampling methods in their ability to provide data at broad spatial scales over a range of temporal resolution over decadal time periods. Recognition of phytoplankton ecological and functional differences has compelled advancements in satellite observations over the past decades to go beyond chlorophyll-a (Chl-a) as a proxy for phytoplankton biomass to distinguish phytoplankton taxa from space. In this study, a multispectral remote sensing approach is presented for detection of dominant phytoplankton groups frequently observed in the nBUS. Here, we use a large microscopic dataset of phytoplankton community structure and the Moderate Resolution Imaging Spectroradiometer of aqua satellite match-ups to relate spectral characteristics of in water constituents to dominance of specific phytoplankton groups. The normalised fluorescence line height, red-near infrared as well as the green/green spectral band-ratios were assigned to the dominant phytoplankton groups using statistical thresholds. The ocean colour remote sensing algorithm presented here is the first to identify phytoplankton functional types in the nBUS with far-reaching potential for mapping the phenology of phytoplankton groups on unprecedented spatial and temporal scales towards advanced ecosystem understanding and environmental monitoring.

Increasing frequency, intensity and duration of marine heatwaves (MHWs) are supposed to affect coastal biological production in different regions to different extents. To understand how MHWs impact coastal primary productivity and community succession of phytoplankton and assess the changes in resilience of phytoplankton communities, we conducted a mesoscale enclosure experiment simulating a marine MHW in the coastal water of southern China. After 8 days of the MHW (+3 o C) treatment, community biomass was significantly lower than the control's, and primary productivity per volume of water was reduced by about 56%. Nevertheless, the phytoplankton community retrieved its biomass and primary productivity after the temperature was subsequently reset to that of the control. Although the MHW treatment decreased the abundance of diatom and increased the percentages of Synechococcus and Prasinophytes, the main phytoplankton functional types showed positive resilience that allowed the recovery of the phytoplankton community after the MHW. Our results indicate that key phytoplankton functional types in the southern coastal waters of China exhibited significant resilience, recovery, and temporal stability under the influence of the marine MHW by 3 o C rise. However, reduced primary productivity during the MHW period, along with decreased biomass density, might significantly influence secondary producers. In addition, the altered phytoplankton community structure may affect coastal food web processes at least during the MHW period., Competing Interests: Declaration of Competing Interest ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Inc.)

The riverine nutrient inputs to the ocean reflects land-use changes and can affect the health of coastal environments over time, especially for a highly-anthropogenically influenced river-estuary-shelf system. To investigate the impact of riverine inputs on the Changjiang Estuary ecosystem at a multi-decadal time scale where long-term observations are limited, we built a three-dimensional physics-biogeochemistry-coupled model system based on the Finite-Volume Community Ocean Model (FVCOM) and the European Regional Shelf Ecosystem Model (ERSEM). Our model successfully simulated the temporal and spatial nutrient variabilities in the river-estuary-shelf con7tinuum from 1960 to 2018. The results showed increasing trends of nitrate and phosphate and fluctuating silicate variability, thereby leading to rising nitrogen (N) to phosphorus (P) ratios and decreasing silicon (Si) to N and P ratios. Such changes in the stoichiometric relationship of nutrient species also alter the community structure of the primary producers in estuaries. Our model showed a general increase of diatoms over the 59 years, corresponding to decreased proportions of micro-phytoplankton and pico- phytoplankton. With different backgrounds of light and nutrient limitations in the river and inner shelf, our model suggests that the trend of the diatom proportion in the light-limited river mouth is more associated with silicate variability, with decreased diatom proportions occurring in the 2000s. Our model relates the hydroclimate, nutrient load, and biogeochemical cycling, reproducing estuarine ecosystem variability and clarifying issues such as the causality of the ecosystem interactions.

Understanding the pollution status and phytoplankton community structure characteristics of discharge tail water in container recirculating aquaculture system is helpful to improve the efficiency of water quality management and increase aquaculture benefits. In this study, water quality monitoring and phytoplankton sampling were carried out at outlet site A and inlet site B of the system. The difference analysis was used to compare the water quality and phytoplankton community structure between the site A and B. Redundancy analysis (RDA ) was used to analyze the correlation between phytoplankton and environmental factors and identify the main environmental factors affecting phytoplankton community structure. The results showed that the main pollutants were suspended solids ( SS ) and total nitrogen ( TN), the pollutant concentration at site A higher than at site B,and the total pollution index was the highest in May. The removal rate of Ammonia nitrogen (NH + 4 -N) and SS in the purification area was higher than another pollutant. In addition,98 species of phytoplankton were detected in the system,including 76 species at site A and 81species at site B,the average phytoplankton density,biomass,Shannon-Wiener diversity index and Margalef richness index were 12. 25×10 6 cell / L and 11. 67×10 6 cell / L,26. 69 mg / L and 34. 23 mg / L,1. 87 and 1. 93,0. 63 and 0. 64 in the site A and B, respectively. SS was an environmental factor that significantly affected the phytoplankton community structure at site A, and NH + 4 - N, TN, total phosphorus ( TP ) and SS were environmental factors that significantly affected the phytoplankton community structure at site B. This research demonstrates that physical filtration and ecological purification can effectively reduce pollutant concentration and improve phytoplankton biodiversity in container recirculating aquaculture tail water. [ABSTRACT FROM AUTHOR]

The primary production by diatoms, haptophytes and cyanobacteria in the Kuroshio region was evaluated using satellite ocean color remote sensing. We developed a method that estimates bio-optical properties such as the photosynthetic quantum yield index and chlorophyll-a-specific optical absorption coefficient of phytoplankton to derive the group-specific production. In contrast with the previous efforts that assume bio-optical properties to derive the production, our method relaxes the assumption by integrating an image processing of bulk satellite data into bio-optical modeling. Especially, our bio-optical model uses a universal bio-optical principle that we found: i.e., the absorption coefficient of phytoplankton at the wavelength of 510 nm can represent their spectral average. Climatological average of the group-specific primary production in the Kuroshio region showed 134, 72 and 40 mg C m–2 day–1 for diatoms, haptophytes and cyanobacteria, respectively. The quantum yield index of each phytoplankton group varied spatially, resulting in a latitudinal gradient, and diatoms had a higher quantum yield than those of cyanobacteria and haptophytes. Analysis of seasonal variability in the group-specific primary production in the Kuroshio region suggested that the primary production due to diatoms was mainly driven by variability in their chlorophyll-a abundance, whereas that due to cyanobacteria by variability in their quantum yield index or photophysiology. The production due to haptophytes was shown seasonally regulated by variability in both chlorophyll-a abundance and photophysiology. [ABSTRACT FROM AUTHOR]

Biogeographical classifications of the global ocean generalize spatiotemporal trends in species or biomass distributions across discrete ocean biomes or provinces. These classifications are generally based on a combination of remote‐sensed proxies of phytoplankton biomass and global climatologies of biogeochemical or physical parameters. However, these approaches are limited in their capacity to account for subsurface variability in these parameters. The deployment of autonomous profiling floats in the Biogeochemical Argo network over the last decade has greatly increased global coverage of subsurface measurements of bio‐optical proxies for phytoplankton biomass and physiology. In this study, we used empirical orthogonal function analysis to identify the main components of variability in a global data set of 422 annual time series of Chlorophyll a fluorescence and optical backscatter profiles. Applying cluster analysis to these results, we identified six biomes within the global ocean: two high‐latitude biomes capturing summer bloom dynamics in the North Atlantic and Southern Ocean and four mid‐ and low‐latitude biomes characterized by variability in the depth and frequency of deep chlorophyll maximum formation. We report the distribution of these biomes along with associated trends in biogeochemical and physicochemical environmental parameters. Our results demonstrate light and nutrients to explain most variability in phytoplankton distributions for all biomes, while highlighting a global inverse relationship between particle stocks in the euphotic zone and transfer efficiency into the mesopelagic zone. In addition to partitioning seasonal variability in vertical phytoplankton distributions at the global scale, our results provide a potentially novel biogeographical classification of the global ocean. Plain Language Summary: Due to the enormous spatiotemporal variability in environmental dynamics within the global ocean, understanding and predicting biological processes at broad scales requires identifying ecologically similar marine provinces. However, because such provinces are typically defined using data from satellites or from climatologies averaging many decades of ship‐based measurements, they are limited in their ability to account for environmental variability beneath the sea surface. Over the last 10 years, the development of the global Biogeochemical Argo (BGC‐Argo) networks of autonomous profiling floats has significantly relieved this constraint, providing measurements of physical, bio‐optical, and biogeochemical parameters within the upper kilometer of the ocean. In this study, we explore the potential for using BGC‐Argo time series data to develop a novel biogeographical classification based on the direct measurement of subsurface bio‐optical parameters. We identify six phytoplankton biomes in the global BGC‐Argo data set: two high‐latitude biomes characterized by large phytoplankton blooms during summer months and four mid‐to‐low‐latitude biomes characterized by complex subsurface dynamics reflecting basin‐scale trends in environmental forcings. Our results capture the environmental drivers of phytoplankton distributions at the global scale, in addition to relationships between phytoplankton distributions in the upper sun‐lit layer of the ocean and particle accumulation within the mesopelagic zone. Key Points: Data from Biogeochemical‐Argo provides a novel basis for defining six biogeographical provinces of the global oceanLight and nutrient fields explain most of the variability in phytoplankton distributions for each provinceSmall particle concentrations in the euphotic zone are inversely related to their transfer efficiency toward the mesopelagic zone [ABSTRACT FROM AUTHOR]

The subsurface chlorophyll maximum (SCM) is increasingly recognised as an important but understudied locus of primary production particularly in shelf seas. Here we report the results of a 4 year, repeat station, summer sampling programme (2013–2016) of a seasonally recurrent SCM in the Western English Channel. Interannual variability in phytoplankton community structure and chlorophyll distribution and intensity was strongly related to water column stability at the depth interval of the SCM and also to water temperature. The phytoplankton community was statistically distinct in each year. High stability, as evidenced by large Richardson numbers and a well-developed strong thermocline appeared to favour the growth of larger dinoflagellates (autotrophs or mixotrophs) and diatoms. Such conditions led to development of the most intense SCMs and these were sometimes dominated by a single or a few key species most prominently in 2015 with near monospecific concentrations of the dinoflagellate Tripos fusus with average peak SCM chlorophyll concentrations of 7.3 ± 4.4 μg l−1. By contrast, in years with low water column stability and intermittent turbulence at the thermocline (2014, 2016) there was greater chlorophyll dispersal and less intense SCM. In these low stability conditions, red fluorescent nano-phytoplankton, such as naked dinoflagellates, chlorophytes and prymnesiophytes, made a greater contribution to the community, possibly as a result of the advantages that motility and enhanced light utilisation efficiency confer within an SCM exposed to turbulence. It is also likely that turbulence disrupted the stability required by the larger dinoflagellates and diatoms. Several of the key SCM taxa were absent from surface waters including the dinoflagellates Tripos fusus , Tripos lineatus , and most of the Rhizosolenia / Proboscia diatoms, consistent with adaptations more suited to survival at depth in stratified waters. These traits include luxury nutrient uptake and storage and survival in low light (both groups) and mixotrophy (dinoflagellates). On the other hand, in 2013, diatoms including Pseudo-nitzschia spp. were abundant in both surface, SCM and bottom waters. The relatively cooler waters (11.6–12.1 °C on average in 2013 and 2016) were characterised by smaller diatoms (Chaetoceros spp. and Pseudo-nitzschia spp.) whereas the warmer waters (13.1 °C on average in 2014) contained larger diatoms (large Rhizosolenia spp., Lauderia annulata and Leptocylindrus danicus). There did not appear to be continuity of key species between years, other than for the dinoflagellate Tripos lineatus , which was significant in both 2013 and 2014 and present in 2015. In any given year, there was no correspondence between the key spring bloom phytoplankton species as monitored in the nearby Western Channel Observatory L4 station and the key SCM taxa. [Display omitted] • Interannual (2013–2016) biological & physical survey of summer stratified shelf sea: Western English Channel. • Phytoplankton community structure of summer subsurface chlorophyll maxima (SCMs) assessed. • Interannual variability in environmental conditions influenced SCM chlorophyll structure and phytoplankton community. • Phytoplankton community structure strongly related to stability at the depth interval of the SCM. • High water column stability at the depth of the SCM, favoured the growth of larger dinoflagellates and diatoms. [ABSTRACT FROM AUTHOR]

Many reports have demonstrated that the removal of aquaculture purse seine is conducive to the restoration of aquatic vegetation and the improvement in water quality, but less attention has been paid to the effects on phytoplankton. This paper addressed the response of phytoplankton community structure to aquatic vegetation restoration after purse seine removal in Caizi Lakes. The results showed that the average dissolved oxygen (from 7.43 ± 0.25 mg/L to 9.12 ± 0.49 mg/L) and Secchi depth (from 28.40 ± 6.20 cm to 47.61 ± 14.62 cm) in the water column of the Caizi Lakes increased after the restoration of aquatic vegetation, while the average concentrations of total nitrogen (from 2.00 ± 0.16 mg/L to 1.34 ± 0.18 mg/L) and total phosphorus (from 0.15 ± 0.02 mg/L to 0.06 ± 0.01 mg/L) decreased. After the restoration of the aquatic vegetation, the cell density of phytoplankton declined from 21.04 ± 4.57 × 106 cells/L to 12.74 ± 3.63 × 106 cells/L, and the biomass fell from 18.13 ± 3.57 mg/L to 9.72 ± 2.55 mg/L. We also observed that Shannon–Wiener diversity, Margalef and Pielou indices of phytoplankton surged by 66.50%, 46.20% and 84.68%, respectively. Because this study demonstrated that aquatic vegetation could alleviate the eutrophication, it can provide guidance for the restoration and protection of the aquatic ecosystem. [ABSTRACT FROM AUTHOR]

The structure of freshwater phytoplankton communities can be strongly influenced by environmental and spatial processes at different scales. To identify the main forces that drive phytoplankton structure becomes a relevant tool to understand several knowledge gaps in the phytoplankton ecology domain, such as community succession, biological invasions and responses to disturbances. We used the morphological‐based functional groups (MBFG) approach to investigate the influence of environmental conditions (physical and chemical factors), nutrient availability and spatial processes (habitat connection and species dispersal) in structuring microphytoplankton community in a subtropical hypereutrophic reservoir located in southern Brazil. Samples were taken quarterly, between February 2017 and December 2018. We used distance‐based multivariate analysis of variance (PERMANOVA) to evaluate potential spatial and seasonal dissimilarities in the MBFG's biovolume, and variation partitioning approach (pRDA) to evaluate the role of environmental, nutrient availability and spatial components in explain the microphytoplankton community structure. We identified 16 microphytoplankton taxa, which were sorted into five MBFGs. Significant seasonal dissimilarities were observed in the MBFG's biovolume. Higher relative biovolume of potential harmful cyanobacteria (MBFG III) and alien dinoflagellates (MBFG V) was observed in summer and autumn/winter, respectively. Pure environmental component (composed by physical and chemical predictors insolation, precipitation, total dissolved solids, turbidity, water temperature, water transparency and wind intensity) explained 45% of the variance in the MBFG's biovolume, whereas pure nutrient availability component explained 7% and spatial component explained only 3% of the biotic variance. The results showed that the environmental factors – especially the seasonal‐influenced ones – are more effective than nutrient availability and spatial processes in explaining the microphytoplankton community structure in this ecosystem. Our findings alert to the need to consider the variability of the environmental conditions (mainly those directly influenced by seasonality) in phytoplankton community structure in disturbed freshwater ecosystems prone to eutrophication events. [ABSTRACT FROM AUTHOR]

Marine phytoplankton play a central role in global biogeochemical cycling, carbon export, and the overall functioning of marine ecosystems. While chlorophyll a (Chl a) is widely used as a proxy for phytoplankton biomass, identifying the proportion of Chl a attributable to different phytoplankton groups remains a major challenge in oceanography, especially for the picophytoplankton groups that often represent the majority of phytoplankton biomass in the open ocean. We describe a method for measuring picophytoplankton per-cell Chl a in field samples using fluorescence-activated cell sorting followed by solvent-based Chl a extraction and fluorescence quantification. Applying this method to surface samples from the Gulf of Mexico, we determined per-cell Chl a to be 0.24 ± 0.07, 0.6 ± 0.33, and 26.36 ± 20.9 fg Chl a cell-1 for Prochlorococcus, Synechococcus, and PPE, respectively (mean ± SD). Measurements of per-cell Chl a using this method are precise to within 1.7, 2.1, and 3.1% for Prochlorococcus, Synechococcus, and PPE, respectively. We demonstrate that this approach can be used to obtain estimates of group-specific Chl a for Prochlorococcus, Synechococcus, and picophytoeukaryotes, the latter two of which cannot be captured by existing methods. We also demonstrate that measurements of per-cell Chl a made using this method in field samples are sufficiently precise to capture relationships between per-cell Chl a and cytometer red fluorescence, providing a bridge between biomass estimates from cell counts and bulk measurements of total Chl a.

A variety of biomarkers of sediment core KET-1 were studied to reconstruct both paleoproductivity and phytoplankton community structure variations and to reflect the local climate change of Kuroshio mainstream of east Taiwan over the past millennium. The results showed that sterols in sediments derived from the mixed terrestrial and marine inputs, with the riverine input from eastern Taiwan as the main terrestrial sterol source. The upward increase of terrestrial organic matter over the past millennium suggested the increasing riverine input of eastern Taiwan. The variation of the marine primary productivity was mainly influenced by the nutrient supplements from the riverine input. The changes of brassicasterol to dinosterol ratio indicated a phytoplankton community shift from dinoflagellate-dominated to diatom-dominated since 1500 CE. The increasing terrestrial inputs and the change of phytoplankton community change over time were related to “dry-humid” climate change.

Many reports have demonstrated that the removal of aquaculture purse seine is conducive to the restoration of aquatic vegetation and the improvement in water quality, but less attention has been paid to the effects on phytoplankton. This paper addressed the response of phytoplankton community structure to aquatic vegetation restoration after purse seine removal in Caizi Lakes. The results showed that the average dissolved oxygen (from 7.43 ± 0.25 mg/L to 9.12 ± 0.49 mg/L) and Secchi depth (from 28.40 ± 6.20 cm to 47.61 ± 14.62 cm) in the water column of the Caizi Lakes increased after the restoration of aquatic vegetation, while the average concentrations of total nitrogen (from 2.00 ± 0.16 mg/L to 1.34 ± 0.18 mg/L) and total phosphorus (from 0.15 ± 0.02 mg/L to 0.06 ± 0.01 mg/L) decreased. After the restoration of the aquatic vegetation, the cell density of phytoplankton declined from 21.04 ± 4.57 × 106 cells/L to 12.74 ± 3.63 × 106 cells/L, and the biomass fell from 18.13 ± 3.57 mg/L to 9.72 ± 2.55 mg/L. We also observed that Shannon–Wiener diversity, Margalef and Pielou indices of phytoplankton surged by 66.50%, 46.20% and 84.68%, respectively. Because this study demonstrated that aquatic vegetation could alleviate the eutrophication, it can provide guidance for the restoration and protection of the aquatic ecosystem.

The rapid pearl farming industry causes environmental pollution to aquatic ecosystems. However, fish-mussel systems with highly productive, profitable and environment-friendly characteristics are appropriate aquaculture practices under the current polluted state of the environment in China. Phytoplankton are excellent indicators and play indispensable roles in maintaining the stability of a freshwater ecosystem. Therefore, samples were seasonally collected determine the seasonal phytoplankton community dynamics and potential driving factors in three subtropical reservoirs with integrated fish-mussel aquaculture. All water physicochemical parameters varied seasonally, and water quality had a trend of eutrophication. A total of 189 species were identified, among which Chlorophyta (83 species) dominated in species richness. Cyanophyta, in particular remained to be highly abundant (57.53% of the total seasonal biomass). The NMDS analysis indicated that summer was an independent branch. The CCA analysis and Spearman rank correlation analysis suggested that water temperature might be the main abiotic factor. Furthermore, pH, conductivity, DO, chlorophyll, TC and TN also significantly affected the community. The aquaculture enhanced the similarity in community structure which have happened due to predation pressure. The present study also identified the potential influences caused by the integrated fish-mussel aquaculture on phytoplankton seasonal succession, bringing some guidance to protect the reservoir ecosystem. [ABSTRACT FROM AUTHOR]

Eutrophication has caused drastic changes to the marine ecosystem of the East China Sea during the past decades. However, there is relatively sparse evidence of historical changes, as well as the explicit effects of climatic changes and anthropogenic activities on the primary productivity of marine coastal ecosystems. In this study, surface and core sediments from the Zhejiang-Fujian coastal mud area, East China Sea coast, were analyzed using the bulk and molecular biomarkers. The results showed that ecosystem changes were characterized by increased phytoplankton productivity and a fluctuant transition from blooms mostly dominated by diatoms to red tide events dominated by dinoflagellates. Variations from the early 1850s to the early 2010s can be divided into a nature-dominated period (the early 1850s–1960s) and a human-impacted period (1960s–the early 2010s). Particularly, natural forcing such as heavy floods (e.g. 1998, 1954, and 1931) in the whole of the Yangtze River catchment, variations in the intensity of East Asia Monsoon, and strengthened or weakened Kuroshio intrusion/positive or negative Pacific Decadal Oscillation phase in the coastal mud area have substantially affected the phytoplankton productivity and community structure during the nature-dominated period. In contrast, changes in nutrient supply and compositions were more apparent during the human-impacted period, which could have been because of increased fertilizer usage, discharges of industrial wastewater and domestic sewage, and large-scale human projects (e.g. Danjiangkou Reservoir and Three Gorges Dam) in the Yangtze River drainage area, leading to significant phytoplankton productivity and community structure variations in the coastal mud area system of East China Sea. [ABSTRACT FROM AUTHOR]

Abstract As mariculture expands offshore in response to the increasing demand for seafood, a new set of ecological concerns arises. We report on presented phosphate and silicate deficiencies in spring in the Zhangzi Island area, northern Yellow Sea, used for farming scallops. Silicon limitation was observed at up to 77.3% of stations, with an average silicate concentration as low as 1.7 μM in March 2014. Average phosphate concentration decreased from 0.12 to 0.05 μM from March to May. Stoichiometric ratios and absolute concentrations indicate that 78%–90% of stations showed phosphate limitation. Correspondingly, the phytoplankton community shifted from predominately diatoms to dinoflagellates. The higher frequency of nutrient limitation in farmed areas, compared with unseeded areas and northern Yellow Sea in general, imply intensified bottom-up controls on scallop production. The "bottle-neck" effect of limited food availability in spring suggests that carrying capacity was originally overestimated, when calculated from annual primary production. Highlights • New ecological concerns accompany expanding offshore mariculture. • Severe silicate and phosphate limitations occur near Zhangzi Island scallop farms. • The natural dominance of diatoms shifts to dinoflagellates as a result. • Bottom-up controls on scallop production intensify. • Carrying capacity based on annual primary production is overestimated. [ABSTRACT FROM AUTHOR]

Abstract The Western English Channel is a seasonally stratified temperate coastal sea where a subsurface chlorophyll maximum (SCM) is typically detectable within the seasonal thermocline. The SCM often develops as a thin layer (< 5 m) that may contain elevated concentrations of phytoplankton (subsurface chlorophyll maximum thin layer; SCMTL). During summer 2013 a study was conducted offshore of Falmouth, UK to assess spatial and short-term temporal variability in SCM thickness in relation to water column structure and physical conditions and to evaluate any associated changes in phytoplankton community structure. SCMTLs were observed in 18 of 52 vertical profiles, typically characterised by higher chlorophyll concentrations than broader SCMs. SCMTLs were generally associated with a 'stepped' thermocline, likely representing the presence of one or more shallow mixed layers forming above/within the seasonal thermocline, and related to increased stratification compared to broader SCMs. Pseudo-nitzschia was almost exclusively the dominant diatom taxon in SCMs, yet statistically distinct differences in community structure existed between SCMTLs and broader SCMs. Within the phytoplankton, the distinction was largely due to a greater biomass of Proboscia alata and other rhizosolenid diatoms, and the dinoflagellate Ceratium lineatum in SCMTLs, and a smaller population of the diatom Chaetoceros spp. There was also a distinction amongst heterotrophic dinoflagellates, with enhanced biomass of Gyrodinium spp. in SCMTLs and a reduction in Diplopsalis lenticula. We propose that this observed difference resulted from promotion of phytoplankton better adapted to environmental conditions more specific to SCMTLs compared to broader SCMs. With more intense and prolonged stratification projected for the NW European shelf, there may be increased prevalence of SCMTLs and the associated larger-sized specialised taxa, with implications for increased carbon export. This study adds to a growing body of evidence of the importance of SCMTLs in coastal and shelf seas, and highlights the requirement for improved understanding of physical forcing and the ecology and physiology of key taxa, particularly as predicted changes in stratification could alter the role of SCM phytoplankton in a future influenced by climate change. Graphical abstract fx1 Highlights • Biological & physical survey of summer stratified shelf sea: Western English Channel (84). • Phytoplankton community structure of subsurface chlorophyll maxima (SCMs) assessed (81). • SCM thin layers (<5 m thick) occur with greatest stratification (64). • SCM thin layers have distinct phytoplankton community structure from broader SCMs (80). • SCM thin layers may expand in importance with predicted increase in stratification (82). [ABSTRACT FROM AUTHOR]

Bivalve aquaculture is an important source of affordable animal protein for coastal community. The success and sustainability of this industry is highly influenced by the suitability of the environment in which it is carried out. Present study was carried out to evaluate the feasibility of green mussel (Perna viridis) farming in Marudu Bay. The site suitability for green mussel farming was evaluated based on biophysical parameters and food availability. The in situ environmental parameters, phytoplankton abundance and composition were collected from 10 sampling stations on monthly interval from May 2014 to April 2015. The results showed that the environmental parameters and food availability in most of the sampling stations were suitable for green mussel. However, the presence of phytoplankton taxa (Chaetoceraceae) which are unfavorable by green mussel in most of the stations located at the bay pocket make those areas less recommended for green mussel farming. In contrast, stations located on the mouth of the bay exhibited high site suitability rating points and hence are highly recommended for cultivation of green mussel.

The subtropical oceans are home to one of the largest ecosystems on Earth, contributing to nearly one third of global oceanic primary production. Ocean warming leads to enhanced stratification in the oligotrophic ocean but also intensification in cross-shore wind gradients and thus in eddy kinetic energy across eastern boundary regions of the subtropical gyres. Phytoplankton thriving in a future warmer oligotrophic subtropical ocean with enhanced CO2 levels could therefore be patchily fertilized by increased mesoscale and submesoscale variability inducing nutrient pumping into the surface ocean. Under this premise, we have tested the response of three size classes (0.2–2, 2–20, and >20 μm) of subtropical phytoplankton communities in terms of primary production, chlorophyll and cell biomass, to increasing CO2 concentrations and nutrient fertilization during an in situ mesocosm experiment in oligotrophic waters off of the island of Gran Canaria. We found no significant CO2-related effect on primary production and biomass under oligotrophic conditions (phase I). In contrast, primary production, chlorophyll and biomass displayed a significant and pronounced increase under elevated CO2 conditions in all groups after nutrient fertilization, both during the bloom (phase II) and post-bloom (phase III) conditions. Although the relative increase of primary production in picophytoplankton (250%) was 2.5 higher than in microphytoplankton (100%) after nutrient fertilization, comparing the high and low CO2 treatments, microphytoplankton dominated in terms of biomass, contributing >57% to the total. These results contrast with similar studies conducted in temperate and cold waters, where consistently small phytoplankton benefitted after nutrient additions at high CO2, pointing to different CO2-sensitivities across plankton communities and ecosystem types in the ocean.

Species composition and biomass of phytoplankton (Bsum), concentration of chlorophyll "a" and nutrients, and hydrophysical conditions were studied on July 5-12, 2011, at 29 stations in the White Sea. The chlorophyll "a" concentration and Bsum in the surface water layer corresponded to the level of phytoplankton bloom (>1 mg/m3 and >30 mg C/m3, respectively), except for two stations. For the first time, the dominance of diatom Thalassiosira angulata by biomass was recorded for a vast area of the White Sea; in the surface layer, the abundance and biomass of this species reached up to 24 × 103 cells/L and 34.56 mg C/m3, respectively. Even higher values (179 × 103 cells/L and 258 mg C/m3) were noted at one of the coastal stations at a 3-m depth. The stability of the water column (positive relation) and salinity (negative relation) were the main factors affecting the spatial variability of the T. angulata biomass. [ABSTRACT FROM AUTHOR]

The Southern Ocean is a hotspot of the climate-relevant organic sulfur compound dimethyl sulfide (DMS). Spatial and temporal variability in DMS concentration is higher than in any other oceanic region, especially in the marginal ice zone. During a one-week expedition across the continental shelf of the West Antarctic Peninsula (WAP), from the shelf break into Marguerite Bay, in January 2015, spatial heterogeneity of DMS and its precursor dimethyl sulfoniopropionate (DMSP)was studied and linked with environmental conditions, including sea-ice melt events. Concentrations of sulfur compounds, particulate organic carbon (POC) and chlorophyll a in the surface waters varied by a factor of 5-6 over the entire transect. DMS and DMSP concentrations were an order of magnitude higher than currently inferred in climatologies for the WAP region. Particulate DMSP concentrations were correlated most strongly with POC and the abundance of haptophyte algae within the phytoplankton community, which, in turn, was linked with sea-ice melt. The strong sea-ice signal in the distribution of DMS(P) implies that DMS(P) production is likely to decrease with ongoing reductions in sea-ice cover along the WAP. This has implications for feedback processes on the region's climate system. This article is part of the theme issue 'The marine system of the West Antarctic Peninsula: status and strategy for progress in a region of rapid change'. [ABSTRACT FROM AUTHOR]

The recent increasing of atmospheric turbulence has had considerable impact on the oceanic environment and ecosystems of the Arctic. To understand its effect on phytoplankton community structure, a Eulerian fixed-point observation (FPO) was conducted on the Chukchi shelf in fall 2013. Temporal and vertical distributions of the phytoplankton community were inferred from algal pigment signatures. A strong wind event (SWE) occurred during the observation term, and significant convection supplied nutrients from the bottom layer to the surface. Before the SWE, pigment composition in the warmer, less saline, and nutrient-poor surface waters was diverse with low concentration of chlorophyll-a (chla). Vertical mixing induced by the SWE weakened the stratification and brought sufficient nutrients to enhance diatom-derived pigment concentrations (e.g., fucoxanthin and chlc3), suggesting increases in diatoms. We also developed a model to predict the distribution of major phytoplankton pigment/chla ratios using a profiling multi-wavelength fluorometer (Multi-Exciter) with higher spatio-temporal resolution. The Multi-Exciter also captured changes in pigment composition with environmental changes at the FPO site and at four observation sites 16 km from the location of the FPO. Furthermore, we investigated the change in grazing rates of the major Arctic copepod Calanus glacialis copepodid stage five to assess the interaction between primary and secondary producers during the fall bloom. Increased diatom biomass caused a significant increase in the grazing rate on microphytoplankton (> 20 µm) and a decrease on nanophytoplankton (2-20 µm), indicative of a strong cascade effect because of the reduction of microzooplankton due to the grazing from C. glacialis. We conclude that SWEs during fall might affect food webs via the alternation of seasonal succession of phytoplankton community structure. [ABSTRACT FROM AUTHOR]

Abstract: Satellite ocean color observations revealed that unusually deep convection events in 2005, 2006, 2010, and 2013 led to an increased phytoplankton biomass during the spring bloom over a large area of the northwestern Mediterranean Sea (NWM). Here we investigate the effects of these events on the seasonal phytoplankton community structure, we quantify their influence on primary production, and we discuss the potential biogeochemical impact. For this purpose, we compiled in situ phytoplankton pigment data from five ship surveys performed in the NWM and from monthly cruises at a fixed station in the Ligurian Sea. We derived primary production rates from a light photosynthesis model applied to these in situ data. Our results confirm that the maximum phytoplankton biomass during the spring bloom is larger in years associated with intense deep convection events (+51%). During these enhanced spring blooms, the contribution of diatoms to total phytoplankton biomass increased (+33%), as well as the primary production rate (+115%). The occurrence of a highly productive bloom is also related to an increase in the phytoplankton bloom area (+155%) and in the relative contribution of diatoms to primary production (+63%). Therefore, assuming that deep convection in the NWM could be significantly weakened by future climate changes, substantial decreases in the spring production of organic carbon and of its export to deep waters can be expected. [ABSTRACT FROM AUTHOR]

The dissolved nitrogen (DN) regime in Jiaozhou Bay (JB) has shifted recently, and the phytoplankton community structure showed decreased diatom and increased dinoflagellate concentrations. This study combined field microcosm experiments, the Nutrients–bi-Phytoplankton–Detritus (NbPD) biogeochemical model, and statistical analysis, and obtained some results. The growth/death of dominant phytoplankton populations were comprehensively determined by the processes of nutrient uptake, excretion and decomposition of phytoplankton in JB. Kinetic parameters indicated that Skeletonema costatum preferentially absorbed NH 4 -N and NO 3 -N, while Protoperidinium pellucidum preferentially absorbed domestic-derived dissolved organic nitrogen. Moreover, S. costatum , as R-strategists, needed a faster uptake rate and slower excretion rate to achieve high growth efficiency but with faster decomposition, while P. pellucidum , as K-strategists, could maintain stability with a more active metabolism. Overall, this study discussed the key factors modulating the diatom dinoflagellate community structure changes in JB, providing a scientific basis for ecosystem-based management. • Impact of dissolved nitrogen on dominant algal species structure in Jiaozhou Bay. • Algal regime shift mechanism with dissolved nitrogen structure in coastal waters. • Skeletonema costatum efficiently absorbed NH 4 -N and NO 3 -N. • Peridinium pellucidum preferentially absorbed domestic-derived dissolved organic nitrogen. • Shift from water quality-based to ecosystem-based environmental management. [ABSTRACT FROM AUTHOR]

Modified clay (MC) technology is an effective method for controlling harmful algal blooms (HABs). Based on field experience, a bloom does not continue after treatment with MC, even though the residual HAB biomass accounts for 20–30% of the initial biomass. Laboratory studies using unialgal cultures have found that MC could inhibit the growth of the residual algal cells to prevent HABs. Nevertheless, the phytoplankton in field waters is diverse. Therefore, unclassified complex mechanisms may exist. To illustrate the molecular mechanisms through which MC controls HABs in the field and verify the previous laboratory findings, a series of experiments and bioinformatics analyses were conducted using bloom waters from aquacultural ponds. The results showed that a 72.29% removal efficiency of algal biomass could effectively control blooms. The metatranscriptomic results revealed that the number of downregulated genes (131,546) was greater than that of upregulated genes (24,318) at 3 h after MC addition. Among these genes, several genes related to DNA replication were downregulated; however, genes involved in DNA repair were upregulated. Metabolism-related pathways were the most significantly upregulated (q < 0.05), including photosynthesis and oxidative phosphorylation. The results also showed that MC reduced most of the biomass of the dominant phytoplankton species, likely by removing apical dominance, which increased the diversity and stability of the phytoplankton community. In addition to reducing the pathogenic bacterial density, MC reduced the concentrations of PO 4 3− (96.22%) and SiO 3 2− (66.77%), thus improving the aquaculture water quality, altering the phytoplankton community structure (the proportion of Diatomea decreased, and that of Chlorophyta increased), and inhibiting phytoplankton growth. These effects hindered the rapid development of large phytoplankton biomasses and allowed the community structure to remain stable, reducing HAB threats. This study illustrates the molecular mechanisms through which MC controls HABs in the field and provides a scientific method for removing HABs in aquacultural waters. [Display omitted] • MC causes oxidative stress to residual algal cells, inhibiting growth. • In residual cells, processes of metabolism and genetic information processing are disordered. • MC improves the water quality and decreases nutrients to inhibit growth and regulate the phytoplankton community structure. • MC removes dominant phytoplankton species to increase the diversity and stability of the phytoplankton community. [ABSTRACT FROM AUTHOR]

In eastern boundary current systems (EBCSs), submesoscale to mesocale variability contributes to cross-shore exchanges of water properties, nutrients, and plankton. Data from a short-term summer survey and satellite time series (January-February 2014) were used to characterize submesoscale variability in oceanographic conditions and phytoplankton distribution across the coastal upwelling and coastal transition zones north of Punta Lavapié, and to explore cross-shelf exchanges of diatom taxa. A thermohaline front (FRN-1) flanked by a mesoscale anticyclonic intrathermocline eddy (ITE-1), or mode-water eddy, persisted during the time series and the survey was undertaken during a wind relaxation event. At the survey time, ITE-1 contributed to an onshore intrusion of warm oceanic waters (southern section) and an offshore advection of cold coastal waters (northern section), with the latter forming a cold, high chlorophyll-a filament. In situ phytoplankton and diatom biomasses were highest at the surface in FRN-1 and at the subsurface in ITE-1, whereas values in the coastal zone were lower and dominated by smaller cells. Diatom species typical of the coastal zone and species dominant in oceanic waters were both found in the FRN-1 and ITE-1 interaction area, suggesting that this mixture was the result of both offshore and onshore advection. Overall, front-eddy interactions in EBCSs could enhance cross-shelf exchanges of coastal and oceanic plankton, as well as sustain phytoplankton growth in the slope area through localized upward injections of nutrients in the frontal zone, combined with ITE-induced advection and vertical nutrient inputs to the surface layer. [ABSTRACT FROM AUTHOR]

Phytoplankton fuel epipelagic ecosystems and affect global biogeochemical cycles. Nevertheless, there is still a lack of quantitative information about the factors that determine both phytoplankton community structure and dynamics, particularly in subtropical gyres. Here, we estimated size fractionated phytoplankton growth ( μ ) and microzooplankton grazing rates ( m ) along a transect in the subtropical North Atlantic, from the island of Hispaniola to the Iberian Peninsula, by conducting dilution experiments and fitting mixed models. We also examined the relationship between nutrient availability and the differences in both phytoplankton community structure and size fractionated phytoplankton growth rates at two spatial scales (i.e. subtropical gyre and within-province spatial scale). Our results revealed high values for both phytoplankton growth and microzooplankton grazing rates. Phytoplankton growth (0.00–1.19 d −1 ) displayed higher variability among stations, biogeochemical provinces and size fractions than the microzooplankton grazing rate (0.32–0.74 d −1 ). Differences in phytoplankton community structure were associated with dissolved inorganic nitrogen (0.72–5.85 μM; R 2 = 0.19) and squared Brunt-Väisälä frequency (R 2 = 0.21) at the whole gyre scale. Conversely, the differences in phytoplankton growth rate showed a weak relationship with those properties (R 2 ⩽ 0.05) at that scale, but a stronger relationship at the within province scale (R 2 ⩾ 0.07). These results support the idea that phytoplankton grow at high rates in oligotrophic subtropical gyres, this is likely due to the selection of phytoplankton groups with functional traits suited to exploit low nutrient availability. Thus, shedding new, multi-scale knowledge on the commonly misunderstood “ocean deserts”. [ABSTRACT FROM AUTHOR]

This work describes the spatial distribution of pigments and main taxonomic groups of phytoplankton in the biogeochemical provinces of the subtropical South Atlantic Ocean, along 30°S latitude. Seawater samples (surface to 200 m depth) were collected along 120 oceanographic stations occupied in the early austral spring of 2011, during a CLIVAR Repeat Hydrography cruise. The pigments were identified and quantified by high performance liquid chromatography (HPLC), and CHEMTAX software was used to determine the relative contributions of the main taxonomic groups to total chlorophyll a (phytoplankton biomass index). Sampling stations were grouped into three provinces: Africa, Gyre, and Brazil, corresponding to the eastern, central, and western sectors of the transect, respectively. Our results showed that both vertical and horizontal distribution patterns of pigments and taxonomic groups were mainly determined by the availability of light and/or nutrients. Photosynthetic carotenoids (PSCs), associated with small flagellates (mainly haptophytes), dominated the light-limited and nutrient-enhanced deep chlorophyll maximum (DCM) layers of both the Brazil and Gyre provinces, as well as the upwelling influenced surface waters of the Africa province. The latter showed the highest chlorophyll a values ​​(>1 mg m –3 ) and abundance of dinoflagellates in the coastal region. Photoprotective carotenoids (PPCs) were predominant in the nutrient-poor and well-lit surface layers of the Brazil and Gyre provinces, associated with a low content of chlorophyll a (~0.1 mg m –3 ) and dominance of prokaryotes ( Synechoccocus and Prochloroccocus ). This study demonstrates that pigment analysis can provide a useful approach to better understand the distribution of phytoplankton communities along physical-chemical gradients in a still undersampled region of the South Atlantic Ocean. [ABSTRACT FROM AUTHOR]