Phytoplankton Assemblages Research Articles

Amino acid nitrogen stable isotopes as biomarkers of coastal phytoplankton assemblages and food web interactions

Marine phytoplankton and zooplankton face rapidly changing environments in the face of global warming and climate change. We investigated the effect of warmer water and lower pH conditions—projected for New Zealand coastal waters at the start of the next century—on both phytoplankton and zooplankton in a 20 d mesocosm experiment to determine whether amino acid stable isotopes could be used as biomarkers of environmental change. We also assessed whether key environmental drivers, such as those linked to climate change, altered the processing of amino acids at the base of the food web. Despite changes in phytoplankton biomass and community composition, we found no significant difference in either particulate organic matter (POM) bulk or amino acid-specific δ15N values, indicating that the trophic status of POM was not significantly influenced by lower pH and warming. Threonine δ15N values were the most sensitive to changes in the phytoplankton community and showed correlations with diatoms (positive) and small flagellates (negative), demonstrating potential as a biomarker for detecting changes related to these phytoplankton groups and thus making threonine a promising indirect indicator of climate change. Finally, δ15NPhe values tracked changes in the lower food web, likely due to faster turnover times, showing its valuable role as a tracer of the nitrogen baseline, even during accelerated metabolism in zooplankton.

Effects of Nile Tilapia (Oreochromis niloticus) on phytoplankton community structure and water quality: a short-term mesocosm study

Nile tilapia is a highly invasive fish species, deliberately introduced into many lakes and reservoirs worldwide, sometimes resulting in significant ecosystem alterations. A short-term mesocosm experiment with and without Nile tilapia (Oreochromis niloticus) was designed to test the hypotheses that the presence of tilapia may affect phytoplankton community structure, increase nutrients availability in water column and deteriorate water quality. Nutrients, total suspended solids (TSS) and biomass of phytoplankton in different size classes (as Chla) were measured. We found that tilapia increased the total nitrogen (TN), total dissolved nitrogen (TDN), NH4+and TSS concentrations, deteriorating the water quality. In addition, under tilapia presence, the biomass of phytoplankton, as well as that of micro- and nano-phytoplankton, increased leading to a change in the structure of the phytoplankton assemblage. Moreover, a reduction in the biomass of periphyton was observed. Omnivorous tilapia is often dominant in tropical and subtropical waters, and removal of this fish may represent an effective management tool to improve the water quality.

Quantification and Visualization of the Variability of Phytoplankton Assemblage in a Semi-lotic Seasonal Canal in Sundarbans, India

Canals of Sundarbans in India are highly vulnerable to anthropogenic pressures which directly or indirectly impact the biological components of such ecosystems. Being at the base of the trophic pyramid, phytoplankton is exposed to environmental stressors and the impact will be reflected in the upper strata of the aquatic food chain. Hence, phytoplankton communities along with their interrelationship with environmental parameters were assessed in Bhetkimari canal, a semi-lotic system in Indian Sundarbans during June 2017 to September 2018. Seventy-seven species under 66 genera were recorded with Cyanophyceae (34%) as a major contributor, followed by Bacillariophyceae (31%) and Chlorophyceae (22%). Diatoms dominated round the year in terms of diversity (25 species) with maximum contribution from Pennales. ANOVA (post-hoc test) showed significant temporal heterogeneity (p≤0.05) in phytoplankton distribution in the canal. The Margalef richness index (d) and Shannon-Weiner diversity index ( H′ ) were 2.59±0.43 and 2.26±0.59, respectively indicating that the environment is good and phytoplankton diversity in the system is moderate. Water temperature, dissolved oxygen, total alkalinity and nutrients (nitrate, silicate and phosphate) were the explanatory variables in shaping the phytoplankton assemblages in the canal, which was evident from Canonical correspondence analysis. The salient findings of this study can add to the existing knowledge on the abundance and distribution pattern of phytoplankton in semi-lotic canal environments, and help in planning better management of canal ecosystems for their sustainable utilization.

Effects of Environmental Parameters on the Seasonal Distribution of Phytoplankton in the Shallow Lake Ketence, Turkey

The seasonal distribution of the phytoplankton and their relationship with environmental parameters of Lake Ketence was studied with monthly intervals in two stations between October 2016 and September 2017. A total of 93 taxa in 8 divisions were identified, and 11 taxa in 4 different divisions (Chlorophyta, Bacillariophyta, Euglenozoa, Miozoa) dominated the phytoplankton in different periods of the study. Main nutrients (NO3-N, NO2-N, TP, Si), some other parameters (T, EC, Secchi disk depth), and organic content of the lake had strong impacts on the distribution of phytoplankton assemblages. Although biomass values varied and indicated very good to very poor water quality during the studied period, especially the prevalence of chlorophytes such as T. minimum which prefer high nutrient and euglenoids such as E. clavata, E. rubra, P. longicauda, and T. oblonga that grew extremely well under high organic content has confirmed that Lake Ketence is eutrophic.

Morphological variability and genetic analysis of Thalassiosira tenera (Bacillariophyta), a dominant phytoplankton species from the northwestern Sea of Japan

ABSTRACT Thalassiosira species significantly contribute to phytoplankton communities, forming algal blooms in temperate and polar regions, and are broadly used as model organisms for nanotechnology and as important food sources in the aquaculture industry. Despite being widespread in the world’s oceans, data on abundance and seasonal patterns of individual species of Thalassiosira are sparse. In the present study, we have identified Thalassiosira tenera from the northwestern Sea of Japan, using light and scanning electron microscopy (SEM), and molecular genetic analysis of 28S rDNA sequence. Based on field and cultured material, morphological variability of T. tenera was studied; a detailed diagnostic description of the species is provided, and its morphometry is compared with that of the morphologically similar T. exigua. Growth peculiarities of the species were investigated in laboratory culture; variations in frustule morphology occur at different growth stages. The degree of frustule silicification is assumed to depend on the stage of cell development. By SEM observations of field samples, the seasonal dynamics of the species was examined and data on its abundance are provided for the first time. Findings indicate that T. tenera is present year-round in the phytoplankton assemblage in the northwestern Sea of Japan. The species dominates the community from November to February, accounting for more than 60% of the total phytoplankton abundance. The highest numbers, 7,281 cells l−1, were recorded under the sea ice in January, and the lowest numbers, less than 100 cells l−1, occurred in April. In addition, the study gives information on the species ecology.

Spatio-temporal Assessment of Phytoplankton and Physicochemical Parameters of Dangana Lake, Lapai, Niger State Nigeria

Dangana Lake was constructed primarily to provide water for drinking, domestic activities and control flood. Phytoplankton assemblage and physicochemical parameters of Dangana Lake, Lapai, Niger State Nigeria were investigated monthly between March and October 2019 using standard methods and procedures. Water samples were collected from 3 different stations in the Lake. The result of the lake shows water temperature (23.2-29.5ºC), Biochemical oxygen Demand (2.30-3.91mg/l), Dissolved oxygen (3.40-4.70mg/l), water pH (6.10-7.5), Electrical conductivity (60.00-121µS/cm), Nitrates (0.30-1.05mg/l) and Phosphate (0.53-1.75mg/l). Temperature, DO, BOD5, and pH shows no significant difference (p>0.05) among sampling sites, however, Electrical conductivity, Nitrate and Phosphate differs significantly among sampling sites (p<0.05). Seasonally there was a significant difference (p<0.05) among sampling months in all the physicochemical parameter measures. A total of Seventeen (17) species of phytoplankton in six (6) families were encountered. The percentage abundant of phytoplankton revealed Bacillariophyta (36.84%), Dinophyta (33.38%), Chlorophyta (17.05%), Heterokontophyta (6.93%) Cyanophyta, (4.76%), and Euglenophyta (1.02%). Phytoplankton population was significantly higher during the dry season than in the raining season. The Canonical Correspondence analysis (CCA) correlated positively between the measured physicochemical parameters and the observed organisms. The nutrient status of the lake shows a medium range as indicated by the measured environmental parameters.

Dissolved organic carbon as a driver of seasonal and multiyear phytoplankton assembly oscillations in a subtropical monomictic lake

AbstractPhytoplankton assembly dynamics in lakes are highly sensitive to variability in climate drivers and resulting physicochemical changes in lake water columns. As climate change increases the frequency of major precipitation events and droughts, many lakes experience increased inputs of colored dissolved organic carbon (CDOC) and nutrients. How these CDOC‐related changes in resources, transparency, and thermal stability affect phytoplankton assemblages, succession, and resilience is understudied, particularly in subtropical lakes. Here, we used time series, multivariate, and trait‐based functional redundancy analyses to elucidate the roles of phytoplankton in ecosystem resilience and determine potential drivers of assemblage shifts in a subtropical monomictic lake with fluctuating CDOC inputs (Lake Annie, Highlands County, Florida, USA). We found that phytoplankton assemblages and successional patterns differed between two dark‐water states (late 2005–mid‐2007, late 2012–2019) bracketing a clear‐water state (mid‐2007–late 2012), caused by shifting CDOC and nutrient concentrations associated with oscillating groundwater levels. Diatoms (Bacillariophyta), which were dominant during the two dark‐water states, nearly disappeared and were replaced by synurophytes during the clear‐water state. Assemblages had greater interannual consistency in the dark‐water states, while mean functional redundancy decreased in the clear‐water state. Seasonal phytoplankton successional changes were also more pronounced and synchronized with seasonal hydrologic shifts in the dark‐water states. Multiyear assemblage shifts occurred more quickly in clear‐to‐dark than dark‐to‐clear state transitions, suggesting phytoplankton in dark‐water states may be more resistant to state transitions or even contribute to dark‐water state resilience via feedback loops.

Variations in Seasonal Phytoplankton Assemblages as a Response to Environmental Changes in the Surface Waters of Minicoy Island, Lakshadweep

Phytoplankton, the primary producers in all aquatic systems, play an important key role in biogeochemical processes that are linked to higher trophic levels and climate variability. The spatio temporal composition and abundance of micro phytoplankton species was examined in relation to physical and chemical surface water variables (i.e., Salinity, temperature and nutrients). The primary objectives of the study were to observe the variations in phytoplankton species assemblages as a response to environmental variables. Hierarchiel cluster analysis and non-metric multidimensional scaling were used to find out distinct seasonal groups based on the composition of phytoplankton. The results indicate that several key environmental factors like temperature, salinity and nutrients like nitrate, nitrite, phosphate and silicate influenced seasonal phytoplankton assemblages within the lagoon waters. The distribution of phytoplankton population showed main groups where the blue green algae populations favored the warmer conditions of pre-monsoon period, whereas the diatom population primarily flourished in the post monsoon and monsoon period. The present study deals with the phytoplankton community structure in the Indian Ocean, Lakshadweep Archipelago, Minicoy Island, particularly in the surface water with respect to environmental variables to understand the region-specific dominant community and its governing environmental settings.

Cell size as driver and sentinel of phytoplankton community structure and functioning

AbstractBody size is a decisive functional trait in many organisms, especially for phytoplankton, which span several orders of magnitude in cell volume. Therefore, the analysis of size as a functional trait driving species’ performance has received wide attention in aquatic ecology, amended in recent decades by studies documenting changes in phytoplankton size in response to abiotic or biotic factors in the environment.We performed a systematic literature review to provide an overarching, partially quantitative synthesis of cell size as a driver and sentinel of phytoplankton ecology. We found consistent and significant allometric relationships between cell sizes and the functional performance of phytoplankton species (cellular rates of carbon fixation, respiration and exudation as well as resource affinities, uptake and content). Size scaling became weaker, absent or even negative when addressing C‐ or volume‐specific rates or growth. C‐specific photosynthesis and population growth rate peaked at intermediate cell sizes around 100 µm3.Additionally, we found a rich literature on sizes changing in response to warming, nutrients and pollutants. Whereas small cells tended to dominate under oligotrophic and warm conditions, there are a few notable exceptions, which indicates that other environmental or biotic constraints alter this general trend. Grazing seems a likely explanation, which we reviewed to understand both how size affects edibility and how size structure changes in response to grazing. Cell size also predisposes the strength and outcome of competitive interactions between algal species. Finally, we address size in a community context, where size‐abundance scaling describes community composition and thereby the biodiversity in phytoplankton assemblages.We conclude that (a) size is a highly predictive trait for phytoplankton metabolism at the cellular scale, with less strong and nonlinear implications for growth and specific metabolism and (b) size structure is a highly suitable sentinel of phytoplankton responses to changing environments.A freePlain Language Summarycan be found within the Supporting Information of this article.

Optical Detection of Harmful Algal Blooms in the Belgian Coastal Zone: A Cautionary Tale of Chlorophyll c3

Phaeocystis globosa is a nuisance haptophyte species that forms annual blooms in the southern North Sea and other coastal waters. At high biomass concentration, these are considered harmful algal blooms due to their deleterious impact on the local ecosystems and economy, and are considered an indicator for eutrophication. In the last two decades, methods have been developed for the optical detection and quantification of these blooms, with potential applications for autonomous in situ or remote observations. However, recent experimental evidence suggests that the interpretation of the optical signal and its exclusive association with P. globosa may not be accurate. In the North Sea, blooms of P. globosa are synchronous with those of the diatom Pseudo-nitzschia delicatissima, another harmful bloom-forming species with similar pigmentation and optical signature. Here we combine new and published measurements of pigmentation composition and inherent optical properties from pure cultures of several algal and cyanobacterial groups, together with environmental spectroscopy data, to identify the pigments generating the optical signals captured by two established algorithms. We further evaluate the association of those pigments and optical signals with P. globosa. We found that the interpretation of the pigment(s) generating the optical signals were incorrect and that previous methods are not specific to P. globosa, even in the context of the phytoplankton assemblage of the southern North Sea. Additionally, we found that the optical and pigment signatures of Phaeocystis species are part of a broad pigmentation trend across unrelated taxonomic groups related to chlorophyll c3 presence, with important consequences for the interpretation of pigment and optical data. We then develop and evaluate an algorithm to detect this pigmentation pattern with minimal influence of co-occurring species and elaborate general recommendations for the future development of algorithms.

Domoic Acid and Pseudo-nitzschia spp. Connected to Coastal Upwelling along Coastal Inhambane Province, Mozambique: A New Area of Concern.

Harmful algal blooms (HABs) are increasing globally in frequency, persistence, and geographic extent, posing a threat to ecosystem and human health. To date, no occurrences of marine phycotoxins have been recorded in Mozambique, which may be due to absence of a monitoring program and general awareness of potential threats. This study is the first documentation of neurotoxin, domoic acid (DA), produced by the diatom Pseudo-nitzschia along the east coast of Africa. Coastal Inhambane Province is a biodiversity hotspot where year-round Rhincodon typus (whale shark) sightings are among the highest globally and support an emerging ecotourism industry. Links between primary productivity and biodiversity in this area have not previously been considered or reported. During a pilot study, from January 2017 to April 2018, DA was identified year-round, peaking during Austral winter. During an intense study between May and August 2018, our research focused on identifying environmental factors influencing coastal productivity and DA concentration. Phytoplankton assemblage was diatom-dominated, with high abundances of Pseudo-nitzschia spp. Data suggest the system was influenced by nutrient pulses resulting from coastal upwelling. Continued and comprehensive monitoring along southern Mozambique would provide critical information to assess ecosystem and human health threats from marine toxins under challenges posed by global change.

Multivariate approach to evaluate the factors controlling the phytoplankton abundance and diversity along the coastal waters of Diu, northeastern Arabian Sea

The present study investigated the phytoplankton assemblage and diversity with physicochemical parameters of Diu coastal waters in different seasons during 2018–19. During the study period, 61 phytoplankton species comprising diatoms (50 sp.), dinoflagellates (8 sp.), and cyanophyceae (3 sp.) were recorded. Diatom was found to be a major community and contributed 79 to 99% of total phytoplankton abundance. Reduction in dinoflagellate and dominance of pennate-diatoms were observed during the monsoon. Chlorophyll-a concentration also showed a similar trend and decreased during the monsoon. However, the phytoplankton abundance was low particularly during the monsoon which might be due to the elevated total suspended solids (TSS) load. Canonical correspondence analysis revealed that diatoms were able to survive in high TSS with the support of high nutrients; while dinoflagellates were limited due to those conditions. Overall, the reduction in phytoplankton abundance, diversity, and biomass was recorded due to the elevated TSS input along the coastal waters of Diu.

Impact of Shifting Subpolar Front on Phytoplankton Dynamics in the Western Margin of East/Japan Sea

A subpolar front (SPF) generated between the East Korea Warm Current (EKWC) and the North Korea Cold Current (NKCC) in the western margin of the East/Japan Sea has shifted northward in recent decades. This study investigated the biomass and composition of the phytoplankton assemblage in relation to hydrological and biogeochemical features in the shallow shelf and slope off the Korean coast from January to June in 2016 and 2017, to determine the mechanistic effects of SPF on spring–summer phytoplankton bloom dynamics. Monthly average depth-integrated chlorophylla(Chla) levels and the contribution of phytoplankton classes revealed bimodal diatom blooms in early spring and summer in the frontal zone. Canonical correspondence analysis showed that the distribution of high Chlawas associated with cold, low-salinity NKCC water in March 2016. No Chlapeak was observed in March 2017 when the warm saline EKWC water mass invaded. These results suggest that the NKCC intrusion acts as a forcing mechanism leading to enhanced phytoplankton biomass in the frontal zone. In contrast, positive correlations of Chlaconcentration with water density and nutrient concentrations suggest that summer blooms were fed by the subsurface chlorophyll maximum (SCM) driven by shoaling of the pycnocline and nitracline. Varying water-column stratification determined the thickness of the SCM layer, driving year-to-year variability in the magnitude of diatom blooms. These findings further suggest that seasonal/interannual variability in the timing of algal blooms affects regional trophodynamics and hence could be an important factor in explaining ecosystem changes in this region.

Variability of bio-optical properties in nearshore waters of the estuary and Gulf of St. Lawrence: Absorption and backscattering coefficients

The inherent optical properties and the optically significant constituents in nearshore zones of the Estuary and Gulf of St. Lawrence (EGSL), eastern Canada, were systematically investigated. Dry-mass concentrations of dissolved organic carbon (DOC), phytoplankton pigments, and suspended particulate matter (SPM) were determined together with the absorption coefficients of chromophoric dissolved organic matter, acdom; non-algal particles, anap; phytoplankton, aphy; and particulate backscattering coefficient, bbp. The sampling design allowed analysis at different spatial scales and considered some intra-regional differences in distinctive zones (subregions) of the EGSL's north shore (separated by ∼ 102 km), as well as within subregions (samples separated by ∼ 100–101 km). Temporal analysis focused on seasonal variability (sampling time separated by ∼ 101–102 days). Optical indices, such as the spectral slopes of acdom and anap, pigment ratios, mass-specific absorption and backscattering coefficients, and particulate matter fractioning (inorganic and organic) allowed a detailed characterization of the dissolved organic matter pool and provided useful information about particulate matter assemblages. The acdom was highly correlated with DOC and was found to have a conservative mixing behavior as the dominant process controlling its distribution, although differences among and within subregions were noted and related to differences in local river endmembers and seasonality. The acdom also dominated the absorption budget, even in long wavelengths of the visible range (e.g., 550 nm). Despite the highly light-absorptive characteristic of the waters, phytoplankton biomass was not negligeable, as shown by the chlorophyll-a (Chla) concentrations means that were almost always greater than 1 mg m−3. Analysis of the spectral shape of aphy and pigment ratios revealed a seasonal modulation in the composition of phytoplankton assemblages and photoacclimation. The optical properties of particulate matter showed a very dispersed relationship when compared to dry-mass concentration proxies in the study area, but the extremely low SPM-specific bbp values encountered were explained by the organic-rich characteristic of the nearshore zones of the EGSL. Short-term variability (atmospheric events) and the hydrodynamical regime also resulted in substantial variability in the optical properties of these areas. Overall, we provide a general parametrization for the relationships among the investigated inherent optical properties and dry-mass concentrations, which, in turn, will provide a baseline for tuning and developing regional remote sensing algorithms for the retrieval of biogeochemically relevant constituents of the water.

Characteristics of phytoplankton assemblages in the central South China Sea

The structural characteristics of phytoplankton communities and their relationship with environmental factors were analysed based on survey data from the central South China Sea in summer 2020. A total of 416 separate taxa from 90 genera and 4 phyla were identified, with an average cell abundance of 572.98 cells/L. The dominant phytoplankton species were Nitzschia spp., Gyrodinium spp., Synedra spp. and Navicula spp. The Shannon-Wiener index ranged from 2.25 to 4.98, and the evenness index varied from 0.48 to 0.93. Correlation analysis showed that total cell abundance was negatively correlated with salinity, nitrate and silicate and was positively correlated with nitrite. Compared with the historical data, Thalassionema nitzschioides was cited repeatedly in previous researches as the dominant species. In addition, the Shannon–Wiener index showed an overall increasing trend over time, and the community structure is becoming more stable.

Microplanktonic diatom assemblages dominated the primary production but not the biomass in an Antarctic fjord

The western Antarctic Peninsula (WAP) fjords, currently threatened by climate change, are known as high krill congregation areas, however, the primary productivity in relation to phytoplankton groups in these coastal areas remains uncertain. To test this, we studied the specific composition, diversity and cellular carbon content of phytoplankton communities in relation to primary production (PP) and growth rates in Andvord Bay, its connection to Gerlache Strait and a near station on the continental shelf during spring (2015) and autumn (2016). Based on the microscopic determination of the relative biomass of the different microalgal taxa we determined three main phytoplankton assemblages that differ in their composition, PP, growth, and spatial and temporal distribution: (1) an assemblage dominated by cryptophytes, with high biomass (59.2 ± 28.2 μgC L−1), intermediate PP (63.1 ± 32 mgC m−3 d−1), and low growth (0.2 ± 1.1 d−1) present in the inner part of the fjord during spring, and related to higher surface water temperatures; (2) an assemblage dominated by microplanktonic diatoms (mainly Odontella weissflogii) with intermediate biomass (40.1 ± 17.2 μgC L−1), high PP (151.2 ± 62.5 mgC m−3 d−1), and high growth (0.9 ± 1 d−1) present from the fjord mouth to the Gerlache Strait waters during spring and in shelf waters during autumn, related to high irradiance and microzooplankton biomass; and (3) an assemblage dominated by dinoflagellates, mainly small gymnodinioids (< 15 μm long), with low biomass (3.5 ± 3.5 μgC L−1), low PP (6.9 ± 5.1 mgC m−3 d−1), and intermediate growth (0.5 ± 0.6 d−1) present in the whole fjord and the Gerlache Strait during autumn and infrequently during spring, related to high meltwater fraction. During both seasons, the highest phytoplankton biomass, richness and productivity in Andvord Bay was located in a frontal area at the fjord's mouth. Overall, the results of this study support the notion that WAP fjords are highly productive, highlighting the role of microplanktonic diatom as the main organic carbon producers, even when they occur in low abundances, due to their photosynthetic potential and higher Carbon-to-Chlorophyll a ratio. Our results, together with previous phytoplankton growth rates measured in the WAP nearshore waters from King George Island to Marguerite Bay, are higher than those measured on the WAP shelf and in the Ross Sea suggesting micro- and macronutrient enrichment from glacial melt maintains high productivity throughout the growth season in fjords. Our results support the hypothesis that climate change could highly affect the coastal WAP ecosystems by changing the balance between more productive phytoplankton assemblages (diatoms) to considerably less productive phytoplankton assemblages (cryptophytes).

Dynamics of phytoplankton community in seasonally open and closed wetlands in the Teesta-Torsa basin, India, and management implications for sustainable utilization.

The present study deals with the broader understanding of phytoplankton assemblage pattern and their ecohydrological interactions in two ecologically distinct floodplain wetlands of Teesta - Torsa basin, India. Analyses of data revealed significant seasonal variations (p ≤ 0.05) of ten water variables (temperature, transparency, pH, conductivity, total dissolved solids, dissolved oxygen, total hardness, total alkalinity, PO4 - P, and SiO4 - Si) in both the wetlands; however, no significant variation was observed among the sampling stations. In total, 128 species of phytoplankton were recorded (118 species belonging to 94 genera in seasonally open; 103 species belonging to 86 genera in closed wetland). Four algal groups, viz. Cyanophyceae, Coscinodiscophyceae, Bacillariophyceae, and Chlorophyceae, were the dominant quantitative component, remarkably influencing the total phytoplankton population in both the wetlands, contributing ~ 87% of total phytoplankton. Species Aulacoseira granulata alone contributed 12 - 41% and 8 - 34% to the total phytoplankton in the seasonally open and closed wetland, respectively, and indicated high organic load in both the wetlands. Altogether thirty-six and thirty-one phytoplankton taxa appeared as major indicators across the seasons for seasonally open and closed wetland, respectively. The indicator taxa (Aulacoseira, Oscillatoria, Dolichospermum, Spirogyra, Synedra, Nitzschia, Navicula, Euglena, Phacus) in both the wetlands hinted that the wetlands are under pollution pressure. The assemblage structure of phytoplankton was related to transparency, NO3 - N, PO4 - P, SiO4 - Si, total dissolved solids, and temperature as evident from BIO - ENV. Furthermore, the marginal test also selected similar variables (depth, transparency, conductivity, PO4 - P, SiO4 - Si) for seasonally open and the variables such as depth, conductivity, total dissolved solids, total alkalinity, and NO3 - N for the closed wetland. The study showed that the seasonal riverine connectivity greatly influences the variations in phytoplankton community in the seasonally open wetland.

The Assessment of Phytoplankton Dynamics in Two Reservoirs in Southern Africa with Special Reference to Water Abstraction for Inter-Basin Transfers and Potable Water Production

Toxic phytoplankton in the aquatic ecosystems are dynamic, affecting water quality. It remains unclear as to how possible toxic phytoplankton assemblages vary vertically and temporally in Swakoppoort and Von Bach dams, located in a dry subtropical desert region in central Namibia. The following variables were analyzed: pH, Secchi depths, turbidity, water temperature, total phosphorus, orthophosphate, chlorophyll-a, phytoplankton cells, and water depths. Cyanobacteria dominated the phytoplankton community in the autumn, winter and spring (dry) and summer (wet) seasons, at all the depth ranges in both dams. Microcystis dominated the vertical and temporal dynamics, followed by Dolichospermum. In the dry seasons, higher cyanobacteria cell numbers were observed in comparison to the rainy season in both dams. Spring blooms of cyanobacteria were evident in the Von Bach Dam while autumn and spring cyanobacteria blooms were observed in the Swakoppoort Dam. In the Swakoppoort Dam, the preferable depth ranges for toxic cyanobacteria species were at 5 to 10 m while in the Von Bach Dam at 0 to 5 m range. The findings of the current study indicate that the traditional selective withdrawal of water in the two dams should be performed with vertical and temporal dynamics of possible toxic cyanobacteria accounted for to aid the abstraction of water with the lowest possible toxic phytoplankton numbers, which could lower the public health risk.

Relative roles of fundamental processes underpinning PEG dynamics in dimictic lakes as revealed by a self-organizing, multi-population plankton model

The longstanding PEG (Phytoplankton Ecology Group) qualitative/conceptual model describes generalized seasonal phytoplankton dynamics in temperate lakes and suggests important mechanisms driving these processes. In the research presented here, we re-created the conceptual PEG dynamics using a novel mechanistic numerical plankton model. The numerical model incorporates only a handful of interacting factors and biological rules. Key model features include seasonally variable temperature, mixing depth, and light, dynamic zooplankton and phytoplankton populations, and multiple dynamic nutrient concentrations. The model design is unique in that it incorporates a population-rich phytoplankton assemblage where life-history traits of members are based on ecological principles (trade-offs between traits), allowing the assemblage to organize over time based on nutrient competition and grazing. Using 50th year solutions to the model solved with fourth-order Runge-Kutta methods, i.e., a period when the dynamics had reached stable non-equilibrium states, sensitivity analyses were run by individually varying model parameters +/- 50% and comparing the effect on model responses of interest. Simulation analyses revealed the important role light and temperature limitation played both early and late in the year controlling plankton biomass. Trade-offs in phytoplankton life-history characteristics determined the composition of the spring bloom under non-nutrient limiting conditions (fast-growing, edible populations dominated) and the post clear-water phase assemblage under low nutrient conditions (slower-growing, less-edible populations dominated). Grazer characteristics, specifically rate of grazing and spring “emergence”, determined the occurrence of the clear-water phase and influenced the post assemblage composition, where a clear-water phase was absent when the grazing rate was low or spring emergence absent, and the highly inedible populations were lost from the assemblage. Hydraulic flushing also played an important role where diminished inflow led to higher richness, evenness and diversity due to greater overwintering of less-edible taxa, which influenced phytoplankton composition during spring bloom, diminishing secondary productivity. These results increase understanding of the relative roles of fundamental mechanisms structuring natural aquatic ecosystems and reinforce the significance of key biotic and abiotic system components of temperate lakes.

Simulated ocean acidification altered community composition and growth of a coastal phytoplankton assemblage (South West coast of India, eastern Arabian Sea).

Marine phytoplankton can be highly sensitive to ocean acidification; however, their responses are diverse and therefore, phytoplankton response study on the regional scale is of high research priority. The present study documented the community shift and growth responses of a natural phytoplankton assemblage from the South West coastal water of India (South Eastern Arabian Sea) under ambient CO2 (A-CO2 ≈ 400 µatm) and high CO2 (H-CO2 ≈ 830 µatm) levels in microcosms during the winter monsoon. A doubling of pCO2 resulted in increased cell density, particulate organic carbon and nitrogen (POC, PON) contents, and C:N ratios. The depleted values of δ13CPOC in the H-CO2-incubated cells indicated a higher diffusive CO2 influx. HPLC marker pigment analysis revealed that the community was microphytoplankton dominated (mostly diatoms); nanoplanktonic prymnesiophytic algae and picoplanktonic cyanobacteria showed insignificant response to the simulated ocean acidification. A high CO2-induced increased growth rate was noticed in 6 diatoms (Leptocylindrus danicus; Rhizosolenia setigera; Navicula sp., Asterionella glacialis, Dactyliosolen fragilissimus, and Thalassiosira sp.). The cell volumes of Thalassionema frauenfeldii, Asterionella glacialis, and Cylindrotheca closterium increased significantly, whereas Rhizosolenia setigera and Thalassiosira sp. showed decreased cell volume at the elevated CO2 levels. These changes in growth rate, cell volume, and elemental stoichiometry could be related to CO2 acquisition and the nutritional status of the cells. Some phytoplankton genera from this region are probably acclimatized to pCO2 fluctuations and are likely to benefit from the future increase in CO2 levels. Higher POC production and increased C:N ratio along with variable cell volume may impact the trophic transfer and cycling of organic carbon in this coastal water. However, a multi-stressor approach in a longer experimental exposure should be considered in future research.