Seasonal Succession Of Phytoplankton Research Articles

Succession characteristics of phytoplankton functional groups and ecological assessment in a cold spring-type urban lake, China.

Phytoplankton functional groups have been increasingly utilized in elucidating and predicting the response of phytoplankton species to environmental conditions and seasonal succession in various aquatic systems including lakes, rivers and reservoirs. However, it is still unclear whether the trait-based functional classification can be applied to spring-type lakes. To understand the temporal and spatial characteristics of phytoplankton functional groups and their responses to environmental factors in spring-type urban lake in northern China, an investigation was conducted in Daming Lake from May 2020 to September 2021. The findings revealed the identification of 98 phytoplankton taxa belonging to 6 phyla, predominantly being Chlorophyta (39.8%), Bacillariophyta (35.7%) and Cyanophyta (15.3%). The dominant species were Microcystis sp., Merismopedia minima, Synedra acus and Scenedesmus quadricauda. These phytoplankton taxa were categorized into 21 functional groups, with 6 dominant functional groups (abbreviated as D, MP, P, J, Lo, and W1). Among them, the functional group D, primarily constituted by S. acus, exhibited absolute predominance. The seasonal succession sequence of the dominant functional groups was as follows: D/P/J/MP/ Lo →→ D/P/W1/MP/Lo/J → D/P/J → D/MP → D/P/MP. Throughout the investigation period, the trophic level index (TLI) ranged from 39.10 to 71.13, and the Q index was from 1.91 to 2.91, both indicating a medium health state for Daming Lake, which was consistent with the evaluation results of the diversity index. The results of redundancy analysis revealed that the main driving factors of phytoplankton FG biomass and composition were water temperature (WT), total nitrogen (TN), transparency (SD), TN:TP (N:P), redox potential (ORP), chemical oxygen demand (CODMn) and pH. The dominance of the functional group D positively correlated with water temperature, TN, CODMn, pH and N:P but negatively correlated with SD. It was observed that functional groups and the Q index can objectively indicate the seasonal succession of phytoplankton and the water quality status of Daming Lake. Our discoveries have significant implications for the comprehension of the effects of urbanization on phytoplankton dynamics and for enhancing lake management practices to foster sustainable urban development.

Seasonal interactions between Quagga Mussel grazing and phytoplankton in western Lake Erie: The view from different measuring technologies

Abstract We measured Quagga Mussel grazing-induced changes in seston concentration in 20-L laboratory mesocosms containing lake water, during May-October, as part of a study to investigate the present role of mussel feeding and nutrient excretion in affecting phytoplankton composition. A variety of measuring methodologies including size-fractionated chlorophyll (< 2, 2-20, and >20 µm), phytoplankton groups by FluoroProbe, cyanobacterial genera by 16S rRNA gene sequencing, and particulate C, N, and P gave us different insights into seasonal phytoplankton dynamics and mussel selective feeding and assimilation. High clearance rates and/or high assimilation rates were seen during late May-early July across all size categories, with high rates seen particularly in cryptophytes and diatoms as revealed by FluoroProbe. Starting in late July cyanophytes dominated the phytoplankton and feeding rate on them was generally zero or low. Sequencing analyses suggested that there was a diverse cyanobacterial community present, with Microcystis, contrary to expectation, dominating only in late June. Cyanobium was the dominant genera at most times during summer-fall, and as expected, Microcystis was rejected by mussels relative to other cyanobacteria. Planktothrix, dominant in spring, was readily ingested as well as Anabaena in late June. We show that a combination of methods is helpful to make progress in understanding plankton succession and grazing. These methods were important adjuncts to microscopic analysis (Carrick et al, this issue). Our results support the hypothesis that dreissenid mussels, when abundant, can affect seasonal succession of phytoplankton shifting composition to cyanobacteria and even changes within the cyanobacterial community; however, impacts are likely modest now due low mussel biomass (Carter et al., this issue). Assimilation of C, N, and P was generally high, which is important for mussel population maintenance.

Physical-biological drivers modulating phytoplankton seasonal succession along the Northern Antarctic Peninsula

The Northern Antarctic Peninsula (NAP) shows shifts in phytoplankton distribution and composition along its warming marine ecosystems. However, despite recent efforts to mechanistically understand these changes, little focus has been given to the phytoplankton seasonal succession, remaining uncertainties regarding to distribution patterns of emerging taxa along the NAP. To fill this gap, we collected phytoplankton (pigment and microscopy analysis) and physico-chemical datasets during spring and summer (November, February and March) of 2013/2014 and 2014/2015 off the NAP. Satellite measurements (sea surface temperature, sea ice concentration and chlorophyll-a) were used to extend the temporal coverage of analysis associated with the in situ sampling. We improved the quantification and distribution pattern of emerging taxa, such as dinoflagellates and cryptophytes, and described a contrasting seasonal behavior and distinct fundamental niche between centric and pennate diatoms. Cryptophytes and pennate diatoms preferentially occupied relatively shallower mixing layers compared with centric diatoms and dinoflagellates, suggesting differences between these groups in distribution and environment occupation over the phytoplankton seasonal succession. Under colder conditions, negative sea surface temperature anomalies were associated with positive anomalies of sea ice concentration and duration. Therefore, based on sea ice–phytoplankton growth relationship, large phytoplankton biomass accumulation was expected during the spring/summer of 2013/2014 and 2014/2015 along the NAP. However, there was a decoupling between sea ice concentration/duration and phytoplankton biomass, characterizing two seasonal periods of low biomass accumulation (negative chlorophyll-a anomalies), associated with the top-down control in the region. These results provide an improved mechanistic understanding on physical-biological drivers modulating phytoplankton seasonal succession along the Antarctic coastal waters.

STUDY OF SEASONAL AND LONG-TERM CHLOROPHYLL VARIABILITY IN THE CASPIAN SEA BASED ON REMOTE SENSING DATA

The patterns of seasonal and long-term variability of phytoplankton in the Caspian Sea have been studied using SeaWiFS and MODIS-Aqua scanners. Chlorophyll “a” concentration (CHL) in the Caspian Sea were calculated by the regional algorithm developed using an array of in situ measurements in different seasons of the year. Maps of the average monthly CHL values over a twenty-two-year period and seasonal variability diagrams were constructed for the Northern, Middle and Southern Caspian Sea. The features of seasonal variability of phytoplankton are analyzed using CHL data. The fundamental differences were mentioned in seasonal variability of phytoplankton in the Northern, Caspian Middle and Southern Caspian. The regularities of the spatial dynamics of CHL throughout the Sea, resulting from seasonal succession of phytoplankton have been studied. The years with significant deviations of the seasonal dynamics of CHL from the average climatic one was identified.

Characterizing coastal phytoplankton seasonal succession patterns on the West Antarctic Peninsula

AbstractIn coastal West Antarctic Peninsula (WAP) waters, large phytoplankton blooms in late austral spring fuel a highly productive marine ecosystem. However, WAP atmospheric and oceanic temperatures are rising, winter sea ice extent and duration are decreasing, and summer phytoplankton biomass in the northern WAP has decreased and shifted toward smaller cells. To better understand these relationships, an Imaging FlowCytobot was used to characterize seasonal (spring to autumn) phytoplankton community composition and cell size during a low (2017–2018) and high (2018–2019) chlorophyll a year in relation to physical drivers (e.g., sea ice and meteoric water) at Palmer Station, Antarctica. A shorter sea ice season with early rapid retreat resulted in low phytoplankton biomass with a low proportion of diatoms (2017–2018), while a longer sea ice season with late protracted retreat resulted in the opposite (2018–2019). Despite these differences, phytoplankton seasonal succession was similar in both years: (1) a large‐celled centric diatom bloom during spring sea ice retreat; (2) a peak summer phase comprised of mixotrophic cryptophytes with increases in light and postbloom organic matter; and (3) a late summer phase comprised of small (< 20 μm) diatoms and mixed flagellates with increases in wind‐driven nutrient resuspension. In addition, cell diameter decreased from November to April with increases in meteoric water in both years. The tight coupling between sea ice, meltwater, and phytoplankton species composition suggests that continued warming in the WAP will affect phytoplankton seasonal dynamics, and subsequently seasonal food web dynamics.

A two‐dimensional morphospace for cyanobacteria and microalgae: Morphological diversity, evolutionary relatedness, and size constraints

Abstract Body metrics are considered as master traits that regulate physiological, behavioural and life history features of planktic cyanobacteria and microalgae. Although the distribution of their morphological traits reflects the various trade‐offs and strategies needed for survival in pelagic habitats, previous methods for quantifying phytoplankton body shape do not adequately represent the intricate details of surface variation that are so important for their nutrient‐ and light‐harvesting capabilities. Therefore, here we provide a new framework to quantify and illustrate the morphological diversity of cyanobacteria and microalgae. Essential components of formulae used for surface area (A = Cs × d2) and volume (V = Cv × d3) calculations are provided by the shape‐specific surface area and volume constants (Cs, Cv). Cs, the surface shape factor, characterises the coarseness of the object surface, and Cv, the volumetric shape factor, characterises the shape deviation from a sphere. Using these morphologically and biologically relevant variables, we defined a two‐dimensional morphological space, in which all three‐dimensional objects have well‐defined positions. By analysing morphologies of taxa representing various forms in major cyanobacterial and microalgal groups, we demonstrated that these groups show considerable differences in the area occupied within the morphospace and these differences are not affected by evolutionary relatedness. We showed that the ratio of surface and volume constants correlated with organism size, suggesting that the development of basic morphologies is constrained by their linear dimensions. Using surface and volumetric shape factors, we created a two‐dimensional Euclidean morphospace in which all three‐dimensional objects have a specific position. Positioning uni‐ and multicellular cyanobacteria and microalgae of various shapes into this morphospace allows their geometrical and ecological limitations to be understood. Because of the close linkage between phytoplankton morphology and ecology, the proposed morphospace may serve as a proxy for an ecospace. Thus, in future the proposed morphospace can be used to visualise current ecological processes such as eutrophication or seasonal succession of phytoplankton.

Stochastic and Deterministic Processes Regulate Phytoplankton Assemblages in a Temperate Coastal Ecosystem.

Assessing the relative contributions of the interacting deterministic and stochastic ecological processes for phytoplankton community assembly is crucial in understanding and predicting community organization and succession at different temporal and spatial scales. In this study, we hypothesized that deterministic and stochastic ecological processes regulating phytoplankton, present seasonal and repeating patterns. This hypothesis was explored during a 5-year survey (287 samples) conducted at a small spatial scale (~15km) in a temperate coastal ecosystem (eastern English Channel). Microscopy and flow cytometry quantified phytoplankton abundance and biomass, while metabarcoding data allowed an extended evaluation of diversity and the exploration of the ecological processes regulating phytoplankton using null model analysis. Alpha diversity of phytoplankton was governed by the effect of environmental conditions (environmental filtering). Temporal community turnover (beta diversity) evidenced a consistent interannual pattern that determined the phytoplankton seasonal structure. In winter and early spring (from January to March), determinism (homogeneous selection) was the major process in the phytoplankton community assembly. The overall mean in the year was 38%. Stochastic processes (ecological drift) prevailed during the rest of the year from April to December, where the overall mean for the year was 55%. The maximum values were recorded in late spring and summer, which often presented recurrent and transient monospecific phytoplankton peaks. Overall, the prevalence of stochastic processes rendered less predictable seasonal dynamics of phytoplankton communities to future environmental change. IMPORTANCE While ecological deterministic processes are conducive to modeling, stochastic ones are far less predictable. Understanding the overall assembly processes of phytoplankton is critical in tracking and predicting future changes. The novelty of this study was that it addressed a long-posed question, on a pluriannual scale. Was seasonal phytoplankton succession influenced by deterministic processes (e.g., abiotic environment) or by stochastic ones (e.g., dispersal, or ecological drift)? Our results provided strong support for a seasonal and repeating pattern with stochastic processes (drift) prevailing during most of the year and periods with monospecific phytoplankton peaks.

Recent Changes of Phytoplankton Bloom Phenology in the Northern High‐Latitude Oceans (2003–2020)

AbstractEighteen years (2003–2020) of data on remotely‐sensed ocean color in high northern latitudes show a significant increase (0.56% yr−1) in double blooms of phytoplankton. Starting in 2015 the rate of increase rose to 1.10% yr−1. Double blooms have become especially prevalent in regions north of 50°N in the North Atlantic, Gulf of Alaska and southern Chukchi Sea. Our correlation analysis suggests that double bloom occurrences are dependent on latitude and seasonal changes in both sea surface temperature (SST) and mixed layer depth (MLD), particularly in the subpolar North Pacific (SNP) and polar oceans (65°–75°N), although we cannot attribute the increased double blooms to specific causes. Single blooms indicated by Chlorophyll a (Chl a) dominate in subpolar‐polar waters and occur close to the timing of the Particulate Inorganic Carbon (PIC) peak (i.e., June–August). In the SNP single bloom, Chl a peaks occur earlier than PIC peaks. This interval was shorter during 2016–2020, which is associated with warming anomalies. In the southern part of the Chukchi Sea, however, we found that PIC peaks occur earlier than Chl a peaks, suggesting a potentially different succession pattern between calcifiers and other functional groups. We speculate that in the near future double blooms of phytoplankton will become a prevalent feature in high‐latitude oceans with concurrent changes in the timing of blooms and seasonal phytoplankton succession in the surface ocean due to climate change.

Diel light cycles affect phytoplankton competition in the global ocean

AbstractAimLight, essential for photosynthesis, is present in two periodic cycles in nature: seasonal and diel. Although seasonality of light is typically resolved in ocean biogeochemical–ecosystem models because of its significance for seasonal succession and biogeography of phytoplankton, the diel light cycle is generally not resolved. The goal of this study is to demonstrate the impact of diel light cycles on phytoplankton competition and biogeography in the global ocean.LocationGlobal ocean.Major taxa studiedPhytoplankton.MethodsWe use a three‐dimensional global ocean model and compare simulations of high temporal resolution with and without diel light cycles. The model simulates 15 phytoplankton types with different cell sizes, encompassing two broad ecological strategies: small cells with high nutrient affinity (gleaners) and larger cells with high maximal growth rate (opportunists). Both are grazed by zooplankton and limited by nitrogen, phosphorus and iron.ResultsSimulations show that diel cycles of light induce diel cycles in limiting nutrients in the global ocean. Diel nutrient cycles are associated with higher concentrations of limiting nutrients, by 100% at low latitudes (−40° to 40°), a process that increases the relative abundance of opportunists over gleaners. Size classes with the highest maximal growth rates from both gleaner and opportunist groups are favoured by diel light cycles. This mechanism weakens as latitude increases, because the effects of the seasonal cycle dominate over those of the diel cycle.Main conclusionsUnderstanding the mechanisms that govern phytoplankton biogeography is crucial for predicting ocean ecosystem functioning and biogeochemical cycles. We show that the diel light cycle has a significant impact on phytoplankton competition and biogeography, indicating the need for understanding the role of diel processes in shaping macroecological patterns in the global ocean.

Biological-physical processes regulate autumn prey availability of spiny icefish Chaenodraco wilsoni in the Bransfield Strait, Antarctic.

This study examines the adaptability of a Southern Ocean predator, which is dependent on Antarctic krill (Euphausia superba), to potential changes in food availability. Muscle fatty acids (FAs) of the spiny icefish Chaenodraco wilsoni collected from three areas in the Bransfield Strait (BS), northern Antarctic Peninsula during February-April 2016 give a good representation of their feeding variability. The compositions of 22:6n3 (DHA) and 20:5n3 (EPA) were both higher in the Transitional Zonal Water with Bellingshausen influence (TBW)-controlled C. wilsoni than in the Transitional Zonal Water with Weddell Sea influence (TWW)-controlled fish. This was positively correlated with photoadaptation and carbon sequestration in TBW-controlled phytoplankton. Results for the FAs 16:1n7, 16:0, DHA and EPA indicate the presence of dinoflagellates in all three areas, suggesting that during late summer and early fall, there is a seasonal phytoplankton succession, where small phytoplankton become dominant, in the BS. In addition, the compositions of some long-chain FAs (>20, such as 20:0, 20:1, 22:0 and 22:1n9) and ∑18 indicated that the food chain based on flagellates and copepods was more apparent in TWW-controlled C. wilsoni, especially the effect of El Niño-Southern Oscillation (ENSO) on the variation of prey communities in TWW-controlled areas. FA markers such as SFA/(PUFA+MUFA), ∑15 + ∑17 and ARA were more pronounced in TWW-controlled C. wilsoni, indicating a more strongly carnivorous and benthic food source. In the TBW-TWW confluence, the complex hydrological structure, including the presence of a large number of mesoscale eddies, allows rich nutrients and krill larvae to remain in it, providing a rich food source for the C. wilsoni. Overall, the FA data of this study show that the diet of C. wilsoni varies in different marine environments, aiding their survivability at the face of climate change.

Community Structure of Phytoplankton and Environmental Impact Factors in Lake Hongze from 2015 to 2020

Lake Hongze is an essential storage lake for the "Eastern Route of the South-North Water Diversion Project" and plays an important role in climate adjustment and flood prevention and control. To study the structural evolution of phytoplankton communities in Lake Hongze and their relationship with environmental factors and to understand the status of the ecosystem of Lake Hongze before the "ten-year fishing ban," monthly monitoring was carried out from 2015 to 2020. During the study period, total nitrogen showed a significant downward trend starting in 2017, the total phosphorus and chemical oxygen demand declined slightly, the water temperature had no obvious change trend, and the water depth and transparency increased from 2015 to 2018 and then declined significantly. A total of 102 genera of phytoplankton in eight phyla were identified, with a total of 310 species. The dominant phytoplankton phyla mainly included Chlorophyta and Bacillariophyta, followed by Cyanophyta and Pyrrophyta. The dominant genera were Scenedesmus, Aulacoseira, Cryptomonas, Cyclotella, Tetraedron, Microcystis, and Dolichospermum. The results of non-metric multidimensional scaling (NMDS) showed that the structural composition of the phytoplankton community differed significantly among years, seasons, and sampling areas, mainly due to the redistribution among dominant genera. NMDS analysis also indicated that variation in the phytoplankton community in Lake Hongze was mainly related to water temperature, total nitrogen, total phosphorus, water depth, and transparency. Total nitrogen, water depth, and phytoplankton community structure were significantly correlated with interannual succession, whereas water temperature, total nitrogen, and phytoplankton seasonal succession were also significantly correlated. Combined with the measures taken by the management department in recent years, the changes in the structure of the phytoplankton community may be related to the removal of the fence and other management and restoration measures in Lake Hongze.

Features of the Seasonal Succession of Phytoplankton in the Crimean Coastal Area (Black Sea) in Years with Different Climatic Conditions (2009-2014)

Features of the Seasonal Succession of Phytoplankton in the Crimean Coastal Area (Black Sea) in Years with Different Climatic Conditions (2009-2014)

Phytoplankton Phenology in the Coastal Zone of Cyprus, Based on Remote Sensing and In Situ Observations

Alterations in phytoplankton biomass, community structure and timing of their growth (phenology), are directly implicated in the carbon cycle and energy transfer to higher trophic levels of the marine food web. Due to the lack of long-term in situ datasets, there is very little information on phytoplankton seasonal succession in Cyprus (eastern Mediterranean Sea). On the other hand, satellite-derived measurements of ocean colour can only provide long-term time series of chlorophyll (an index of phytoplankton biomass) up to the first optical depth (surface waters). The coupling of both means of observations is essential for understanding phytoplankton dynamics and their response to environmental change. Here, we use 23 years of remotely sensed, regionally tuned ocean-colour observations, along with a unique time series of in situ phytoplankton pigment composition data, collected in coastal waters of Cyprus during 2016. The satellite observations show an initiation of phytoplankton growth period in November, a peak in February and termination in April, with an overall mean duration of ~4 months. An in-depth exploration of in situ total Chl-a concentration and phytoplankton pigments revealed that pico- and nano-plankton cells dominated the phytoplankton community. The growth peak in February was dominated by nanophytoplankton and potentially larger diatoms (pigments of 19’ hexanoyloxyfucoxanthin and fucoxanthin, respectively), in the 0–20 m layer. The highest total Chl-a concentration was recorded at a station off Akrotiri peninsula in the south, where strong coastal upwelling has been reported. Another station in the southern part, located next to a fish farm, showed a higher contribution of picophytoplankton during the most oligotrophic period (summer). Our results highlight the importance of using available in situ data coupled to ocean-colour remote sensing, for monitoring marine ecosystems in areas with limited in situ data availability.

Independent components of spatial-temporal structure of chlorophyll a patterns in the upper layer of the north-western shelf of the Black Sea

In the present study, the results of independent component decomposition of satellite-derived chlorophyll a (Chla) patterns for the north-western part of the Black Sea are presented. The study has been carried out on the basis of the DINEOF-reconstructed dataset of 8-day average log-transformed Chla (alChla) patterns for 1997-2016. The alChla patterns were decomposed into six independent components of its spatio-temporal variability in the north-western shelf of the Black Sea. The independent components reflect the spatial distribution of alChla anomalies which are likely to be formed under the influence of sea circulation factors driven by wind. The paper presents the results of the analysis of the intra-annual variability of independent components. The interpretation of the patterns of intra-annual independent components variability is given, taking into account the seasonal variability of the wind factor, the flow of the Danube, the Dnieper and Southern Bug rivers and the fact of modulation of independent components dynamics by seasonal phytoplankton succession.

Особливості сезонної сукцесії фітопланктону в прибережній зоні Криму (Чорне море) у різні за кліматичними умовами роки (2009–2014)

Under conditions of climatic changes, it is of great interest to study the dynamics of various functional complexes of phytoplankton species. The long-term influence of previous cold winters on the course of the seasonal succession of phytoplankton, as well as the intensity of blooms in the open waters of the Black Sea, were shown earlier. In the coastal zone, this relationship has not yet been sufficiently studied. Based on regular monitoring studies in the coastal area of Sevastopol from 2009–2014, features of the course of seasonal succession of phytoplankton in years with different climatic conditions were revealed: the “cold” years differed from the “warm” ones by a longer dominance of diatom complexes in terms of cell abundance, especially of small-celled species, which characterize the initial stage of seasonal succession of phytoplankton. The level of development of both diatoms and dinoflagellates was minimal compared to other years, with a shift in the periods of maxima to later months. In contrast, the "warm" years were characterized by the predominance of dinoflagellates for most of the study period, with a shift in timing of the maxima to earlier months. Both diatoms and dinoflagellates reached their maximal development in “warm” years in spring and autumn. In the “moderate” years, phytoplankton development proceeded either by analogy with the “cold” (2009) or “warm” (2011) years. The seasonal succession described above is typical for the northwestern Black Sea, in particular, the Sevastopol coastal area, and differs from the average pattern for the northwestern part described earlier for 1992–1993. The difference consisted of an increase in the proportion of stages I and III due to a decrease in stage II compared to 1992–1993.

Metagenomic analysis provides functional insights into seasonal change of a non-cyanobacterial prokaryotic community in temperate coastal waters.

The taxonomic compositions of marine prokaryotic communities are known to follow seasonal cycles, but functional metagenomic insights into this seasonality is still limited. We analyzed a total of 22 metagenomes collected at 11 time points over a 14-month period from two sites in Sendai Bay, Japan to obtain seasonal snapshots of predicted functional profiles of the non-cyanobacterial prokaryotic community. Along with taxonomic composition, functional gene composition varied seasonally and was related to chlorophyll a concentration, water temperature, and salinity. Spring phytoplankton bloom stimulated increased abundances of putative genes that encode enzymes in amino acid metabolism pathways. Several groups of functional genes, including those related to signal transduction and cellular communication, increased in abundance during the mid- to post-bloom period, which seemed to be associated with a particle-attached lifestyle. Alternatively, genes in carbon metabolism pathways were generally more abundant in the low chlorophyll a period than the bloom period. These results indicate that changes in trophic condition associated with seasonal phytoplankton succession altered the community function of prokaryotes. Our findings on seasonal changes of predicted function provide fundamental information for future research on the mechanisms that shape marine microbial communities.

Cold and wet: Diatoms dominate the phytoplankton community during a year of anomalous weather in a Great Lakes estuary

As sentinels of climate change and other anthropogenic forces, freshwater lakes are experiencing ecosystem disruptions at every level of the food web, beginning with the phytoplankton, a highly responsive group of organisms. Most studies regarding the effects of climate change on phytoplankton focus on a potential scenario in which temperatures continuously increase and droughts intersperse heavy precipitation events. Like much of the conterminous United States in 2019, the Muskegon River watershed (Michigan, USA) experienced record-breaking rainfall accompanied by unusually cool temperatures, affording an opportunity to explore how an alternate potential climate scenario may affect phytoplankton. We conducted biweekly sampling of environmental variables and phytoplankton in Muskegon Lake, a Great Lakes Area of Concern that connects to Lake Michigan. We compared environmental variables in 2019 to the previous eight years using long-term data from the Muskegon Lake Observatory buoy, and annual monitoring excursions provided historical phytoplankton data. Under cold and wet conditions, diatoms were the single dominant division throughout the entire growth season – an unprecedented scenario in Muskegon Lake. In 10 of the 13 biweekly sampling days in 2019, diatoms comprised over 75% of the phytoplankton community in the lake by count, indicating that the spring diatom bloom persisted through the fall. Additionally, phytoplankton seasonal succession and abundance patterns typically seen in this lake were absent. In a world experiencing reduced predictability, increased variability, and regional climate anomalies, studying periods of extreme weather events may offer insight into how natural systems will be affected and respond under future climate scenarios.

Diverse drivers of phytoplankton dynamics in different phyla across the annual cycle in a freshwater lake

An understanding of the annual variations in the phytoplankton community in freshwater lakes, and of the drivers responsible for these variations, is essential for lake management. In this study we collected and analyzed seasonal samples of phytoplankton and assessed environmental variables in Nansi Lake from 2011 to 2015, in order to identify the seasonal dynamics of the phytoplankton community and the main drivers in each phylum. The results showed that phytoplankton diversity in Nansi Lake followed annual cycles, which were interrupted by a water diversion in 2013. The disruption of equilibrium was clearly demonstrated by the Shannon–Wiener diversity index, Pielou’s evenness index, and Simpson’s dominance index, whereas the species richness and abundance showed resilience, maintaining regular annual cycles. The dominant species were frequently Synedra acus Kütz (Bacillariophyta), Closterium gracile Bréb (Chlorophyta), and Scenedesmus quadricauda Bréb (Chlorophyta) in summer and autumn. Non-metric multidimensional scaling (NMDS) analysis suggested that the phytoplankton was most widely distributed in summer, when conditions were more conducive to phytoplankton growth and reproduction. Redundancy analysis (RDA) indicated that the main drivers for the phytoplankton community varied in different taxonomic units. Specifically, the NP ratio and permanganate index (CODMn) had significant effects on Chlorophyta, whereas pH, dissolved oxygen (DO), and transparency significantly influenced Bacillariophyta. This study highlights the importance of seasonal phytoplankton succession and the need for identification of the main drivers in each phylum in order to achieve more effective control of phytoplankton blooms in freshwater lakes.

Iron operates as an important factor promoting year-round diazotrophic cyanobacteria blooms in eutrophic reservoirs in the tropics

We hypothesize that iron availability plays an important role in driving phytoplankton structure and dynamics in tropical reservoir. This role has often been neglected in routine monitoring of water quality since the main focus has been addressed on macronutrients such phosphorus and nitrogen. To elucidate the potential regulation exerted by iron availability on phytoplankton, a limnological investigation was carried out in two neighboring eutrophic reservoirs in tropical China. Traditional physical and chemical variables were measured along with total and dissolved iron concentrations to explore how they could influence phytoplankton structure. Statistical analyses showed that dissolved iron (DFe) as well as dissolved nitrogen (DIN) and soluble reactive phosphorus (SRP) significantly explained the variance of phytoplankton assemblages in both reservoirs. We could also find that diazotrophic cyanobacteria blooms generally developed when DFe concentrations were above 0.025 mg/L. Moreover, the DFe availability in the water columns was modulated by the effects exerted by the stratification/circulation patterns on redox conditions and pH values. Anaerobic conditions favored the release of iron and phosphorus from sediments, and likely favored an enhanced nitrogen assimilation and a decrease of DIN in the epilimnion. Our results highlighted that iron functions as an important factor promoting diazotrophic cyanobacteria and driving seasonal phytoplankton succession in tropical eutrophic reservoirs, not only with a direct effect on phytoplankton growth but also indirect effect by modifying the availability of nitrogen and phosphorus.

Quantifying seasonal succession of phytoplankton trait‐environment associations in human‐altered landscapes

AbstractIntegration of species traits in direct gradient analysis generates insights into how communities are assembled and may respond to environmental changes. We investigated phytoplankton trait‐environment relationships for over 300 taxa during the open‐water season across 75 north‐temperate lakes and reservoirs in Alberta, Canada. An innovative, data‐driven approach was applied using iterative model selection for RLQ optimization to reveal key monthly associations. Fourth‐corner analysis then tested the significance of relationships using spatially and phylogenetically constrained null models derived by Moran spectral randomization. Both local‐ and regional‐scale drivers of succession were found with evidence of deterministic filtering by traits increasing in mid‐summer. Trait associations to land‐use and water quality highlighted potential anthropogenic cross‐scale interactions, such as logging and pasture development affecting phytoplankton via allochthonous nutrient inputs. Biogeographic factors (e.g., elevation and habitat size) and associated temperature and chemical gradients (e.g., pH and bicarbonate) were also linked to multiple morphological, physiological, and behavioral traits, including potential toxin production. Several correlated traits emphasized importance of trait syndromes corresponding to distinct taxonomic groups (e.g., cyanobacteria and green algae). However, rather than clustering species with shared ecological preferences or roles, our study builds on past trait‐based approaches to phytoplankton by testing for explicit trait associations with a range of environmental factors. Thus, we provide a novel, quantitative means of revealing environmental constraints on communities and translating their compositional changes under climate and other human influences into functional impacts on freshwater ecosystems.