Phytoplankton Functional Groups Research Articles

Analytical population dynamics underlying harmful algal blooms triggered by prey avoidance

A modified version of the NPZD ecosystem model is used to analytically examine the effects of predation avoidance, a possible mechanism for triggering harmful algal blooms (HAB). To resolve HAB development caused by predation avoidance, an additional phytoplankton functional group is considered, one that has slower nutrient uptake and better predation avoidance characteristics than the non-harmful phytoplankton group used in traditional NPZD models. Because the two phytoplankton groups (one non-harmful and one HAB) compete for only one resource within the same system, steady state (equilibrium) conditions cannot occur without the presence of zooplankton; only the non-harmful phytoplankton group, which defeats the HAB group in the resource competition, can survive in the equilibrium. The presence of sufficient zooplankton effectively acts to replenish the nutrient pool by consuming the non-harmful phytoplankton. When this occurs, two equilibrium states are found: one with both phytoplankton groups coexisting, and one that only includes the HAB group. The condition required for equilibrium is that the total nitrogen within the system should be larger than a threshold determined by model coefficients. The threshold and feasibility of the equilibrium are sensitive to the relative HAB predation avoidance coefficient. If the coefficient is larger than the ratio of net growth rates between the HAB and non-harmful phytoplankton group, the threshold becomes infinite, and an equilibrium is not feasible. The time scale for the system to reach an equilibrium state that includes a HAB group is determined asymptotically. The dependence of a threshold condition as a controlling factor may explain the regime shift of dominant species causing HABs. The ecosystem model is fully implemented into the Regional Ocean Modeling System and applied to an idealized coastal embayment (with depths and geometry taken from San Francisco Bay) to show numerically the dominance of prey avoidance dynamics in a natural shallow water environment that includes advection and diffusion. The analytical results improve strategies for HAB modeling and provide guidance for setting model coefficients necessary to resolve a HAB event.

EDNA metabarcoding revealed the seasonal and spatial variation of phytoplankton functional groups in the Chai river and their relationship with environmental factors

Environmental DNA (eDNA) metabarcoding permits a new measurement to monitor biodiversity in aquatic ecosystems. This study utilized eDNA metabarcoding to examine the seasonal and spatial distribution of phytoplankton and their relationship with environmental factors in the Chai River, Kunming, China, in the dry, and wet seasons. The process detected 108 genera of phytoplankton, which were members of 11 phyla, 41 orders, and 60 families. Distinct differences in seasonal and spatial distribution patterns of phytoplankton diversity, including community structure, α-diversity, and representative functional groups, were observed. In the dry season, Pseudanabaena, Microcystis, and Synechococcus were the predominant genera in Cyanophyta, and Chlorophyta, Bacillariophyta and Euglenophyta were predominant in the eukaryotic phytoplankton. While in the wet season, Cylindrospermopsis, Microcystis, and Planktothrix predominated in the Cyanophyta, and Bacillariophyta, Chlorophyta and Xanthophyta predominated in the eukaryotic phytoplankton. Significant differences were shown by a principal coordinate analysis and PERMANOVA test among the upper, middle, and lower reaches of the phytoplankton communities except for the cyanobacterial community structure between the upper and lower reaches at the wet season (p > 0.05). The representative functional groups of phytoplankton varied from A, D, E, LM, L0, N, S1, MP, P, TB, TC, U, W0, W1, Xph, Y, and Z in the dry season to A, B, D, E, F, J, MP, LM, S1, SN, TC, P, W0, W1, X2, and Y in the wet season. Significant differences in the water temperature (WT), pH, chemical oxygen demand, oxygen consumed, nitrate nitrogen (NO3-N), and chlorophyll a were exhibited between the dry and wet seasons (p < 0.05). In the dry season, WT, NO3-N, and pH had a substantial influence on the functional groups LM, N, and L0 of the cyanobacteria. The EC and total nitrogen (TN) had a substantial influence on the functional groups A and Y of the eukaryotic phytoplankton. In the wet season, the electrical conductivity (EC), TN, and dissolvable total phosphorus (DTP) primarily affected the functional groups LM and S1, while EC, DPI, and soluble reactive phosphorus had a substantial influence on the functional groups A and Y. This study provides insights on the conservation of phytoplankton diversity and healthy management of the Chai River.

How does aquaculture activity affect phytoplankton functional groups in Gaoyou Lake, China

Aquaculture in lakes is an important human activity that could accelerate eutrophication. Its impacts on aquatic ecosystems have attracted extensive attention. This study was carried out in Gaoyou Lake, China. We investigated environmental variables and phytoplankton in areas with different aquaculture intensities over four seasons. Marked differences in diversity, biomass and phytoplankton community structure were observed across areas. The 59 phytoplankton taxa identified could be divided into 20 functional groups (PFGs), of which groups B, D, E, J, MP, P, S1, W1 and Y were dominant PFGs in different areas. Total phosphorus (TP), ratio of nitrogen and phosphorus (TN/TP) and chemical oxygen demand (CODMn) were important driving factors for spatial differences in phytoplankton functional groups. Aquaculture altered the phytoplankton community structure, leading to a significant increase in phytoplankton biomass and diversity, especially cyanobacterial biomass. However, phytoplankton biomass and diversity could be significantly reduced and restored to natural levels after the cessation of aquaculture. This study clarified the effects of aquaculture activity on the phytoplankton community, thereby providing fundamental information for better understanding the impacts of aquaculture on lake eutrophication.

Impounding Impacts of the Three Gorges Reservoir on Phytoplankton Function Groups and Its Relationship with Resource Use Efficiency

In order to investigate the relationship between phytoplankton community functional group compositions and resource use efficiency in important tributaries of the Three Gorges Reservoir, phytoplankton and environment parameters were sampled from five tributaries, the Xiangxi River, Daning River, Meixi River, Pengxi River, and Huangjin River, in August and November, 2020. There were 119 species (variants) belonging to 62 genera and 7 phyla identified in summer, whereas 118 species (variants) belonging to 7 divisions of 58 genera were found in winter. According to Padisak's theory, all phytoplankton were divided into 25 functional groups, of which there were six important functional groups in both summer and winter:L0, H1, D, Y, MP, and P in summer and L0, H1, A, M, MP, and Y in winter. The α-diversity of the phytoplankton functional group in summer was higher than that in winter. Moreover, a higher α-diversity was also found in downstream samples relative to that in upstream samples, indicating that the community structure was more complex, and the community stability was relatively better in downstream regions of the rivers. Redundancy analysis (RDA) showed that the environment factors, i.e., ν, pH, permanganate index, WT, and RUETN, significantly affected phytoplankton functional groups (P<0.05). Variance partitioning analysis (VPA) indicated that environmental factors had a higher explanatory degree for the change in functional group composition in summer (45.23%); on the contrary, resource use efficiency had a higher explanatory degree in winter (42.33%). The linear fitted model showed that functional groups L0, H1, D, and Y showed a significant positive correlation relationship with RUETN and RUETP in summer, whereas only four functional groups (M, MP, Y, and A) had a linear relationship with RUETP, and all function groups had a good linear relationship with RUETN in winter. These results indicated that the functional groups belonging to cyanobacteria, dinoflagellates, and cryptophyta were more efficient at using limited resources in summer, whereas the diatoms had a good linear relationship with resource use efficiency and formed a dominant group in the low temperature environment of winter. These results suggest that the impounding of the Three Gorges Reservoir area can significantly change the resource use efficiency of phytoplankton, resulting in changes in the phytoplankton functional group composition and community structure.

Impacts of small dams on the phytoplankton and invertebrates in an Amazonian river

AbstractThe construction of small hydroelectric plants (SHPs) has increased greatly worldwide, and the impacts of these impoundments can cause changes in the aquatic biota. Here, we investigated the ecological attributes (abundance, richness, and species diversity) of three communities (phytoplankton, invertebrates in the water column, and benthos) and the functional groups of phytoplankton, before and after the construction of five SHPs in an Amazonian river. The communities were sampled at two sites, one upstream and another downstream of each dam or construction site, before the dam closure. The dam did not change the limnological factors, and the acid waters and low electrical conductivity, typical of “cerrado” rivers, were characteristic of both the pre‐ and post‐dam phases. For aquatic communities, the phytoplankton abundance increased and the diversity of groups decreased in the post‐dam phase. Regarding the morphology‐based functional groups (MBFG), there was an increase in groups I (small algae with a high surface/volume ratio) and V (phytoflagellates), with a reduction in groups VI (diatoms) and VII (large mucilaginous colonies) in the post‐dam phase. The relative abundance of zooplankton species increased in the post‐dam phase, and the opposite was observed for the benthic community, with reductions in abundance, richness, and group diversity in the post‐dam phase. The structure of the three communities differed between the pre‐ and post‐dam phases, but no difference in communities' similarity was observed between the upstream and downstream sites in both phases. The results show that the change in hydrodynamics, from lotic to semi‐lentic, in the reservoirs of the SHPs, was the main driving force for the alterations in the three communities. For phytoplankton, SHPs are favorable in the sense of decreasing the incidence of algal blooms, particularly of cyanobacteria.

Optimized Microcystis Prediction Model Using EFDC-NIER and LH-OAT Method

The National Institute of Environmental Research (NIER) has improved the Environmental Fluid Dynamic Code (EFDC) source code (version 20100328) released by Dynamic Solutions International (https://www.ds-intl.biz). Based on this, a new source code, known as EFDC-NIER, can simulate the vertical migration mechanisms of multiple algal species and cyanobacteria. Along with the vertical migration mechanisms of multiple algal species and cyanobacteria, new parameters are added to the EFDC-NIER model. As the phytoplankton functional group (PFG) concept is adopted, a method to predict Microcystis spp. cell count and parameter calibrations is required. The existing parameter calibration processes for water quality modeling are labor-intensive and time consuming, as the calibration depends on each user's experience, and require repeated manual changes to the parameters of the model. Such manual calibration tends to aggravate the uncertainty in the modeling results. Therefore, this study adopted the Latin-Hypercube One-factor-At-a-Time (LH-OAT) method to construct model sets for parameter calibration. A graphical user interface (GUI) system was also developed for automatic model parameter set configuration, model construction, and modeling, with suggestions for optimal parameters based on the simulation results. The proposed method and tools reported in this study will be useful to determine an optimal parameter interval and values to predict the cell counts of harmful cyanobacteria, such as Microcystis spp.

Water quality assessment using phytoplankton functional groups in the middle-lower Changjiang River, China

The Changjiang River (CR) is the third longest and fifth largest river in the world. However, assessments of its water quality, especially those based on relatively large-scale investigations, are still limited. Our study illustrated the phytoplankton community structure in the CR and assessed its ecological status using the phytoplankton assemblage index for rivers (Qr index). Samples were collected at 85 sites covering the middle-lower CR in May 2017. The total phytoplankton biomass was higher in the lower section of the river and was characterized by diatoms and cryptophytes. In terms of Reynolds functional groups, the phytoplankton biomass was dominated by TB, Y, D, and MP, which accounted for 31%, 23%, 13%, and 11% of the mean total biomass, respectively. The ecological status was generally “good” in the CR, with a mean Qr of 3.70, which was higher in the middle section. Generalized linear models showed significant positive correlations between Qr and RFGs with the highest F value, i.e. TB and P (both p values<0.001). Qr showed an absence of correlation with the phytoplankton biomass, which was low in our study. The results of our study suggested that Qr can be used in ecological assessments in the CR, which will benefit local water quality assessments.

Responses of phytoplankton functional groups to water level fluctuations in the Xiangxi Bay, Three Gorges Reservoir

Responses of phytoplankton functional groups to water level fluctuations in the Xiangxi Bay, Three Gorges Reservoir

Bottom-up and top-down effects on codetermination of the dominant phytoplankton functional groups in Lake Erhai

Bottom-up and top-down effects on codetermination of the dominant phytoplankton functional groups in Lake Erhai

Characterization of phytoplankton functional groups in a tropical shellfish harvesting estuary (Ashtamudi) and adjacent nearshore waters (southwest coast of India).

A pioneering study on phytoplankton marker pigments, by adopting the HPLC-CHEMTAX analytical approach, was carried out in one of the major shellfish harvesting estuaries (Ashtamudi estuary-AE) on the southwest coast of India and also its adjacent nearshore waters (< 20m depth) to study the dynamics of phytoplankton functional groups (PFGs). The AE, in general, appeared to be warm (> 29°C) during the non-monsoon seasons, along with the prevalence of higher salinity (> 25) and NH4-N (> 5µM) levels. However, during the summer monsoon (SM), the prevailing substantial river influx converted the AE into a low salinity (< 10) dominated system, provided with enhanced levels of NO3-N (4.6-12.6µM) and PO4-P (0.2-1.4µM), specifically on its upper reaches. The dissolved inorganic nitrogen (DIN) in the AE was mainly comprised of ammonium (NH4-N), approximately up to ~ 81.8% of the DIN, regardless of seasons, which signifies the eutrophic state of the estuary, the upstream sampling locations, in particular. Concerning the phytoplankton community, a pronounced spatio-temporal variation in chlorophyll a biomass was discernible in the AE, with an exceptional increase (6.4-12.1mgm-3) during the SIM period. The prevalence of a conspicuous increase in chlorophyll a (av. > 5mgm-3) along with enhanced zeaxanthin (av. > 1.5mgm-3) recorded in the AE during the non-monsoon (specifically SIM period) season apparently signified the characteristic governance of cyanobacterial community. During the SM period, the estuary sustained more or less similar concentrations of certain marker pigments, i.e. alloxanthin, zeaxanthin, fucoxanthin and chl b, which representing the co-occurrence of cryptophytes, cyanobacteria, diatoms and chlorophytes, respectively. In contrast, the nearshore waters, wherein enhanced nitrate (NO3-N) and phosphate (PO4-P) levels prevailed, irrespective of seasons, sustained dominance of fucoxanthin over other marker pigments, which indicated the numerical supremacy of diatoms. The CHEMTAX analysis, adopted for estimating the chlorophyll a equivalents of various PFGs, corroborated the supremacy of cyanobacterial derived chlorophyll a in the estuary, and it was conspicuous during the non-monsoonal seasonal periods. Even though the estuary has shown remarkable spatio-temporal hydrographic inconsistencies, that variability was not much operative in generating extreme changes in the nutrient components and subsequent phytoplankton community compositions. From the conspicuous increase in N:P and Si:P ratios, resulting mainly from the low levels of P, it can be concluded that the AE has been a P-limited system for phytoplankton growth (especially for large-sized phytoplankton, e.g. diatoms and dinoflagellates), mainly during the non-monsoonal seasonal periods. Perhaps, this P-limitation, along with the prevalence of warm water column and enhanced NH4-N levels, could be the potential causes of the preponderance of cyanobacterial populations in the AE.

Main functional groups of the plankton in front of the fishing port of Anconcito, Santa Elena-Ecuador

Coastal marine plankton is an indicator of the link in the pelagic food chains of the first level (phytoplankton) and the second trophic level (zooplankton); therefore, it is of great ecological, fisheries and economic importance. In this context, the objective of this study was to describe the main components of two plankton communities (phytoplankton and zooplankton) and environmental variables (temperature, salinity, oxygen) at three distances (1, 5 and 10 miles) off the fishing port of Anconcito from May 2019 to February 2020, as an indicator of the ecosystem health of a fishing sector. Samples were collected horizontally using plankton nets with 55 and 300 μm mesh eyes for 10 minutes. Temperature, salinity, pH and dissolved oxygen were measured in situ with a multiparameter probe at the surface level. Mean temperature values were recorded among the three study areas of 25°C, salinity of 31 ups, dissolved oxygen of 4.6 mg.L-1 and pH of 8.The results showed that the first trophic level recorded the abundance of centric diatoms, considered indicators of productive zones mainly in August, while their density in the other months was lower. The phytoplankton composition recorded 167 species; only 12 species of centric diatoms and 13 species of dinoflagellates recorded higher algal density (&gt; 2%), with 142 species present/scarce, the same that evidenced slight differentiation in the three zones. Therefore, diatoms and dinoflagellates were the phytoplankton functional groups that contributed a heterogeneous diversity index in the three sites. Twenty-three zooplanktonic groups were identified, with an average of six species of jellyfish, twelve siphonophores, two cladocerans, two appendicularians and various larval forms of different taxa. Copepods presented the highest mean abundance (48639.3 ind. (100m3 )-1 and 33.3 % respectively), followed by invertebrate eggs (48434.3 ind. (100m3 )-1 and 36. The ANOSIM analysis showed that there is no significant difference between the population densities of the three fixed stations, and in the Bonferroni pairwise comparison between stations 1 and 10 miles, there is no significant difference. In contrast, between stations (10 and 5), (5 and 1) miles there are significant differences, through the SIMPER application, it was found that the group that contributed to the dissimilarity was the copepods, with 38.29% between stations of 10 and 5 miles. The principal component analysis reported that the groups of cladocerans, crustaceans, mollusks, quetognathans, jellyfish and ichthyoplankton were associated with temperature. In conclusion, this line of research on phytoplankton and zooplankton recorded nutritional indicators such as diatoms and copepods very important in the trophic web, combined with local ecological and oceanographic aspects, indicate that the state of health of the coastal margin in front of Anconcito Bay is optimal.

Phytoplankton Community Structure and Its Relationship with Environmental Factors in Nanhai Lake

In order to determine the characteristics of phytoplankton community structure in Nanhai Lake in Baotou City and its relationship with environmental factors, water and phytoplankton samples were collected and composition and biomass were investigated at six sites in the spring, summer, and autumn of 2021. This article used correlation analysis and redundancy analysis (RDA) combined with the community turnover index (BC) to analyze the phytoplankton functional groups. The results showed that 7 phyla and 68 genera of phytoplankton were identified in the water body, of which Chlorophyta, Bacillariophyta, Cyanobacteria, Chrysophyta, Euglenophyta, Cryptophyta, and Pyrrophyta accounted for 34%, 32%, 16%, 6%, 4%, 4%, and 3%, respectively. The phytoplankton in the water body was classified into 23 functional groups, of which MP and D functional groups were the long−term dominant functional groups, indicating that the habitat is a turbid water body. The ecological state index (Q) value ranged from 1.94 to 3.13, with an average value of 2.74. The comprehensive nutritional index (TSIM(∑)) was between 49.32 and 52.11, with an average value of 51.72, indicating that Nanhai Lake was in a mesotrophic state. Correlation analysis and redundancy analysis (RDA) showed that multiple nutrients, transparency (SD), chemical oxygen demand (COD), water temperature (WT), and Chlorophyll a (Chl−a) were the main environmental factors affecting the biomass of dominant functional groups in the water body. The study showed the characteristics of the functional groups of algae in a precious urban lake in arid and semi−arid areas of China and their relationship with environmental factors (physical and chemical indicators, anions and cation ions, and heavy metal ions), and provided a scientific basis for its water quality evaluation.

Will a heavy sediment load affect responses of phytoplankton functional groups to aquatic environmental changes in different water body types?

Sediment, as a natural component of rivers, directly affects the abundance and function of phytoplankton by altering water physicochemical properties. Despite mounting evidence for the sensitivity of phytoplankton to environmental factors, the responses of phytoplankton functional groups to complex environmental changes in rivers with a heavy sediment load are still poorly understood. Herein, the effectiveness of phytoplankton functional groups was evaluated as an indicator of aquatic environmental changes in a heavily sediment-laden river. Samples were collected from 44 sites (22 free-flowing river sections and 22 man-made reservoir sections) with a mean annual sediment concentration of 4.69 kg m-3 in the Yellow River, China. A total of 31 phytoplankton functional groups were classified during spring (April-May) and autumn (September-October) in 2019. Groups C, MP, and D, which are well adapted to strong water disturbances and turbid habitats, showed distinct advantages over other groups. Despite no significant differences in many environmental variables between the river and reservoir sections, these variables (especially nitrogen nutrients) had remarkable effects on the phytoplankton community structure. The phytoplankton functional groups were sensitive to environmental changes even under sediment interference, although geo-climatic variables also exhibited non-trivial effects. The mean niche breadth of the abundant taxa (river: 11.16; reservoir: 7.93) was higher than that of the rare taxa (river: 5.64; reservoir: 4.86) in different water bodies. Thus, growth and diffusion of the abundant taxa played paramount roles in maintaining ecosystem stability. The results indicate that, in a large-scale sediment-laden river, phytoplankton functional groups can effectively indicate changes in the aquatic environment of either a free-flowing river or a man-made reservoir.

Phytoplankton functional groups structures and ecological quality of tropical lake (Taabo, Côte d’Ivoire)

Phytoplankton functional groups structures and ecological quality of tropical lake (Taabo, Côte d’Ivoire)

Longitudinal Variations in Physiochemical Conditions and Their Consequent Effect on Phytoplankton Functional Diversity Within a Subtropical System of Cascade Reservoirs

The social and environmental impacts of large dams are quantifiable and have been well documented, while small dams have often been presumed to be less environmentally damaging than large dams. The purpose of this study was to analyze longitudinal gradients in environmental, hydrodynamic variables and their impact on phytoplankton function, within a cascade of four reservoirs (XuanMiaoGuan, XMG; TianFuMiao, TFM; XiBeiKou, XBK; ShangJiaHe, SJH) and one reservoir bay (Huangbohe Bay, HBH), located from upstream to downstream in the Huangbo River, Hubei Province, China. Our results showed that water temperature, total nitrogen, and soluble silicate increased along the cascade reservoir system, while the concentration of dissolved oxygen and total phosphorus decreased. We identified 16 phytoplankton functional groups, and the predominant groups, including D (Synedra and Stephanodiscus hantzschii), E (Dinobryon divergens), Lo (Dinoflagellate: Peridinium bipes and Peridiniopsis), X2 (Chroomona), and Y (Cryptomonas), changed longitudinally from up to down in the cascade reservoirs. The number of dominant functional groups increased along the longitudinal gradient, indicating that the function of the phytoplankton community was more stable. Functional group D was the dominant phytoplankton functional group among the four reservoirs, and Lo group was dominant except SJH. The phytoplankton functional groups in the HBH have been completely changed due to the backwater jacking of the main stream of the Yangtze River. Euphotic depth, suspended solids, and nutrients were apparently the key factors driving variations in phytoplankton functional groups among the reservoirs. Notably, the patterns we observed were not all consistent with the cascading reservoir continuum concept (CRCC) that typically characterizes large rivers. Thus, our findings contribute to the further theoretical development of the CRCC, which may not apply widely to all cascade systems.

Functional Groups of Phytoplankton and Their Relationship with Environmental Factors in Lake Maninjau, West Sumatra, Indonesia

Lake Maninjau is a eutrophic lake indicated by the frequent occurrence of cyanobacterial blooms. The phytoplankton functional groups (FGs) reflect the environmental characteristics and can be useful to monitor the trophic state and evaluate lake’s environmental conditions. This study aims to perceive the composition of phytoplankton FGs and their relation to the environmental factors in Lake Maninjau. The data including phytoplankton and environmental factors were collected in 2001, 2005, 2009, 2014, 2015, 2016, and 2018. There were 21 FGs of phytoplankton recorded in Lake Maninjau. FGs of D, J, F, and NA were commonly found in this Lake. The phytoplankton FGs reflected the dynamic of the environmental characteristics of the lake. The FGs NA representative of oligo to mesotrophic habitat type were predominated accounting for 66.3% to 67.69 % in May 2005 with the lake’s conditions characterized by low TP concentration, high Secchi depth and TN: TP ratio. The FGs of M representative of eutrophic to hypereutrophic habitat type were predominated accounting for 74.14 % to 94.96 % in April 2018 with the lake’s conditions characterized by high TP concentration, low TN: TP ratio, and Secchi depth. A canonical correspondence analysis (CCA) showed that temperature, conductivity, and total phosphorus are important environmental factors to have influenced the succession of phytoplankton FGs in Lake Maninjau.

The Differential Responses of Coastal Diatoms to Ocean Acidification and Warming: A Comparison Between Thalassiosira sp. and Nitzschia closterium f.minutissima.

Marine diatoms are one of the marine phytoplankton functional groups, with high species diversity, playing important roles in the marine food web and carbon sequestration. In order to evaluate the species-specific responses of coastal diatoms to the combined effects of future ocean acidification (OA) and warming on the coastal diatoms, we conducted a semi-continuous incubation on the large centric diatom Thalassiosira sp. (~30 μm) and small pennate diatom Nitzschia closterium f.minutissima (~15 μm). A full factorial combination of two temperature levels (15 and 20°C) and pCO2 (400 and 1,000 ppm) was examined. The results suggest that changes in temperature played a more important role in regulating the physiology of Thalassiosira sp. and N. closterium f.minutissima than CO2. For Thalassiosira sp., elevated temperature significantly reduced the cellular particulate organic carbon (POC), particulate organic nitrogen (PON), particulate organic phosphate (POP), biogenic silica (BSi), chlorophyll a (Chl a), and protein contents, and the C:N ratio. CO2 only had significant effects on the growth rate and the protein content. However, for the smaller pennate diatom N. closterium f.minutissima, the growth rate, POC production rate, and the C:P ratio significantly increased with an elevated temperature, whereas the cellular POP and BSi contents significantly decreased. CO2 had significant effects on the POC production rate, cellular BSi, POC, and PON contents, the C:P, Si:C, N:P, and Si:P ratios, and sinking rate. The interaction between OA and warming showed mostly antagonistic effects on the physiology of both species. Overall, by comparison between the two species, CO2 played a more significant role in regulating the growth rate and sinking rate of the large centric diatom Thalassiosira sp., whereas had more significant effects on the elemental compositions of the smaller pennate diatom N. closterium f.minutissima. These results suggest differential sensitivities of different diatom species with different sizes and morphology to the changes in CO2/temperature regimes and their interactions.

Automatic recognition of flow cytometric phytoplankton functional groups using convolutional neural networks

AbstractThe variability of phytoplankton distribution has been unraveled by high‐frequency measurements. Such a resolution can be approached by automated pulse‐shape recording flow cytometry (AFCM) operating at hourly sampling resolution. AFCM records morphological and physiological traits as single‐cell optical pulse shapes that can be used to classify cells into phytoplankton functional groups (PFGs). However, the associated manual post‐processing of the data coupled with the increasing size and number of datasets is time‐consuming and error‐prone. Machine learning models are increasingly used to run automatic classification. Yet, most of the existing methods either present a long training process, need to manually design features from the raw optical pulse shapes, or are dedicated to images only. In this study, we present a convolutional neural network (CNN) to classify several PFGs using AFCM pulse shapes. The uncertainties of manual classification were first estimated by comparing experts' recognition of six PFGs. Consensual particles from the manual PFG classification were used to train and validate the CNN. The CNN obtained competitive performances compared to other models used in the literature and remained robust across several sampling areas, and instrumental hardware and settings. Finally, we assessed the ability of this classifier to predict phytoplankton counts at a Mediterranean coastal station and from a cruise in the South‐West Indian Ocean, providing a comparison with the manual classification over 3‐month periods and a 2h frequency. These promising results strengthen the near real‐time observation of PFGs, especially required with the increasing use of AFCM in monitoring research programs.

Metabolic responses of plankton to warming during different productive seasons in coastal Mediterranean waters revealed by in situ mesocosm experiments

The response of coastal lagoon plankton communities to warming was studied during two in situ mesocosm experiments in spring and fall of 2018 in the Mediterranean. Phytoplankton biomass, gross primary production (GPP), community respiration (R), phytoplankton growth (µ), and loss (l) rates were estimated using high-frequency chlorophyll-a fluorescence and dissolved oxygen sensors, and daily sampling was used to evaluate the nutrient status and phytoplankton pigment functional groups. Warming strongly depressed the dominant phytoplankton functional groups, mainly the prymnesiophytes, diatoms (spring), and green flagellates (fall). It favored minor groups such as the dinoflagellates (spring) and diatoms (fall). In spring, warming depressed GPP and R by half; however, µ (+ 18%) and l (+ 37%) were enhanced. In contrast, both GPP and µ were enhanced by 21% and 28%, respectively, in fall, and no effects were observed for R and l. Warming strongly decreased phytoplankton biomass and oxygen production in spring, and enhanced them, to a lesser extent, in fall. This led to an overall loss of production over both seasons. This study improves understanding of the contrasting effects of warming during two productive seasons, which depend on plankton community composition and interactions between components and environmental conditions.

Succession characteristics of phytoplankton functional groups and water quality responsiveness evaluation in an artificial constructed wetland-reservoir ecosystem

ABSTRACT The artificial constructed wetland-reservoir ecosystem has become a research hotspot in the field of the pretreatment of micro-polluted water. In this study, the water purification efficiency and phytoplankton dynamics, the succession characteristics of phytoplankton functional groups and water quality responsiveness evaluation were investigated. The results showed that the Yanlong project can effectively purify water, and there were significant spatial differences in DO, pH, turbidity and transparency (P<0.001), while the temporal differences in water temperature, DO, electrical conductivity, TP and NH4 +-N were the most significant (P<0.001). B, D, P, MP, X1, J and Lo were consistently dominant FGs, Group I, Group IV, Group V and Group VI were dominant MBFGs throughout the year. The results indicated that MBFG was better than that of the FG while water temperature, pH and BOD5 were the key environmental factors. Overall, our findings could provide important implications to improve sustainable safety of drinking water sources.