Phytoplankton Succession Research Articles

Reduced primary productivity and notable resilience of phytoplankton community in the coastal water of southern China under a marine heatwave

Increasing frequency, intensity and duration of marine heatwaves (MHWs) are supposed to affect coastal biological production in different regions to different extents. To understand how MHWs impact coastal primary productivity and community succession of phytoplankton and assess the changes in resilience of phytoplankton communities, we conducted a mesoscale enclosure experiment simulating a MHW in the coastal water of southern China. After 8 days of the MHW (+3 °C) treatment, community biomass was significantly lower than the control's, and primary productivity per volume of water was reduced by about 56%. Nevertheless, the phytoplankton community retrieved its biomass and primary productivity after the temperature was subsequently reset to that of the control. Although the MHW treatment decreased the abundance of diatom and increased the percentages of Synechococcus and Prasinophytes, the main phytoplankton functional types showed positive resilience that allowed the recovery of the phytoplankton community after the MHW. Our results indicate that key phytoplankton functional types in the southern coastal waters of China exhibited significant resilience, recovery, and temporal stability under the influence of the marine MHW by 3 °C rise. However, reduced primary productivity during the MHW period, along with decreased biomass density, might significantly influence secondary producers. In addition, the altered phytoplankton community structure may affect coastal food web processes at least during the MHW period.

Phytoplankton in Deep Lakes of the Dinaric Karst: Functional Biodiversity and Main Ecological Features.

Phytoplankton is a polyphyletic group of organisms that responds rapidly to environmental conditions and provides a reliable response to changes, making it a good ecological indicator for water quality monitoring. However, a gradient is almost essential for a reliable relationship between pressure and impact. In a low-gradient environment, ingenuity is required to outsmart the limitations of the commonly used linear relationship. Here, we examine changes in biomass and functional biodiversity by analysing larger data sets (2013-2022) in six ecologically diverse, natural, deep Croatian karst lakes with low nutrient gradients using nonlinear correlation coefficients and multivariate analyses in 209 samples. We found that phytoplankton biomass was most strongly influenced by nutrients, salinity and alkalinity, while light availability and total nitrogen strongly influenced phytoplankton functional biodiversity. An additional analysis of the TN:TP ratio revealed that the oligotrophic Lake Vransko is nitrogen-limited, and lakes Kozjak and Prošće are phosphorus-limited. This further clarified the relationship of phytoplankton to nutrients despite the low gradient. The complex analysis in this study provides a new perspective for predicting changes in the structure and succession of phytoplankton in deep karst lakes for successful management under apparent anthropogenic pressure and climate change.

Patchiness of plankton communities at fronts explained by Lagrangian history of upwelled water parcels

AbstractThe transport of plankton by highly dynamic (sub)mesoscale currents—often associated with fronts and eddies—shapes the structure of plankton communities on the same time scales as biotic processes, such as growth and predation (days–weeks). The resulting biophysical couplings generate heterogeneities in their finescale distributions (1–10 km), or “patchiness.” Here, we test the hypothesis that cross‐frontal plankton patchiness at a front found 200–250 km offshore in the California Current System was influenced by wind‐driven upwelling conditions upstream of the front. We show that in situ Eulerian measurements (cross‐frontal transects) can be interpreted in a Lagrangian framework by using satellite‐derived current velocities to trace water parcels backward in time to their coastal origins. We find that the majority of the water parcels sampled at this front originated along the central California coast during different episodic wind‐driven upwelling pulses and followed various trajectories before converging temporarily at the front. In response to nutrient injections at the coast, plankton communities transformed during their journeys from the coast to the sampling zone, with a succession of phytoplankton and zooplankton blooms. The cross‐frontal sampling captured the convergence of these distinct water parcels at different points in their biological histories, which resulted in the observed spatial patchiness. Our results suggest that identifying the processes controlling frontal plankton communities requires understanding them in the context of their spatial and temporal histories. In particular, Lagrangian approaches should be more widely applied to understand critical ecological patterns in highly dynamic systems.

Intensified effect of nitrogen forms on dominant phytoplankton species succession by climate change

Nutrient proportion, light intensity, and temperature affect the succession of dominant phytoplankton species. Despite these insights, this transformation mechanism in highly turbid lakes remains a research gap, especially in response to climate change. To fill this gap, we investigated the mechanism by which multi-environmental factors influence the succession of dominant phytoplankton species in Lake Chagan. This investigation deployed the structural equation model (SEM) and the hydrodynamic-water quality-water ecology mechanism model. Results demonstrated that the dominant phytoplankton species in Lake Chagan transformed from diatom to cyanobacteria during 2012 and 2022. Notably, Microcystis was detected in 2022. SEM revealed the primary environment variables for this succession, including water temperature (Tw), nutrients (total nitrogen (TN), total phosphorus (TP), and ammonia nitrogen (NH4N)), and total suspended solids (TSS). Moreover, this event was not the consequence of zooplankton grazing. An integrated hydrodynamic-water quality-bloom mechanism model was built to explore the mechanism driving phytoplankton succession and its response to climate change. Nutrients determined the phytoplankton biomass and dominant species succession based on various proportions. High NH4N:NO3N ratios favored cyanobacteria and inhibited diatom under high TSS. Additionally, the biomass proportions of diatom (30.77 % vs. 22.28 %) and green (30.56 % vs. 23.30 %) decreased dramatically. In contrast, cyanobacteria abundance remarkably increased (35.78 % to 51.71 %) with the increasing NH4-N:NO3-N ratios. In addition, the proportion of non-nitrogen-fixing cyanobacteria was higher than that of the nitrogen-fixing cyanobacteria counterparts when TN:TP≥20 and NH4N:NO3N ≥ 10. Light-limitation phenotypes also experienced an increase with the rising NH4N:NO3N ratios. Notably, the cyanobacterial biomass reached 3–6 times that in the baseline scenario when the air temperature escalated by 3.0 °C until 2061 under the SSP585 scenario. We highlighted the effect of nitrogen forms on the succession of dominant phytoplankton species. Climate warming will increase nitrogen proportion, providing an insightful reference for controlling cyanobacterial blooms.

High-frequency monitoring reveals phytoplankton succession patterns and the role of cryptophyte in a subtropical river reservoir

Shifts in phytoplankton biodiversity drive frequent community successions within aquatic ecosystems. While significant progress has been made in understanding the factors influencing phytoplankton growth under controlled conditions, the processes driving phytoplankton succession in natural waters remain poorly understood. To address this gap, we conducted high-frequency monitoring of the phytoplankton community in the Jiangdong River Reservoir (Southeast China) from 2021 to 2022. High-frequency data captured 17 complete cycles of phytoplankton growth and decline. Our analysis showed that cryptophytes, though not the dominant group, played a key role in shaping the temporal dynamics of phytoplankton community structure and abundance. The relative abundance of cryptophytes consistently mirrored fluctuations in total chlorophyll-a concentrations. Rainfall-induced low-light conditions enhanced the competitive advantage of cryptophytes. Throughout each cycle of phytoplankton changes, cryptophytes leveraged this short-term advantage to proliferate by utilizing available ammonia nitrogen, ascending from the fourth to the second most abundant group. However, as ammonia nitrogen levels declined to 0.1 mg/L, cryptophyte populations began to decline. These new findings highlight the critical role of cryptophytes in driving phytoplankton succession patterns.

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 Shifts in Diatom Species Dominance in the Tidal Mangrove Estuary of Bangladesh

Sustainable estuary management provides fishery resources, supports livelihoods and maintains estuarine food webs. However, these are highly dependent on hydrological factors and nutrients effects of the estuary itself. We studied seasonal phytoplankton quantity and composition of the Pasur River estuary in the Sundarbans mangrove forest, Bangladesh to understand the phytoplankton structure and identify potential indicators of environmental changes. Water and phytoplankton samples were collected at 11 different locations around the study region from January to December 2019 to assess spatial and temporal differences. Significant differences (p < 0.05) in the average salinity were observed between the dry and rainy seasons. Elevated phytoplankton (blue-green algae) concentrations were associated with decreased salinity while increased diatom abundance was linked to higher salinity. Phytoplankton succession from blue-green algae (wet season) to diatoms (dry season) occurred due to variations in physicochemical parameters and nutrient factors. Simultaneously, phytoplankton diversity and density were shown to change in response to habitat quality and seasonal variation. This study highlights the potential impacts of both human activities and natural factors on the population structure in these estuarine environments. J Bangladesh Agril Univ 22(2):231-240, 2024

Taxonomic difference in marine bloom-forming phytoplanktonic species affects the dynamics of both bloom-responding prokaryotes and prokaryotic viruses.

The production of dissolved organic matter during phytoplankton blooms and consumption by heterotrophic prokaryotes promote marine carbon biogeochemical cycling. Although prokaryotic viruses presumably affect this process, their dynamics during blooms are not fully understood. Here, we investigated the effects of taxonomic difference in bloom-forming phytoplankton on prokaryotes and their viruses. We analyzed the dynamics of coastal prokaryotic communities and viruses under the addition of dissolved intracellular fractions from taxonomically distinct phytoplankton, the diatom Chaetoceros sp. (CIF) and the raphidophycean alga Heterosigma akashiwo (HIF), using microcosm experiments. Ribosomal RNA gene amplicon and viral metagenomic analyses revealed that particular prokaryotes and prokaryotic viruses specifically increased in either CIF or HIF, indicating that taxonomic difference in bloom-forming phytoplankton promotes distinct dynamics of not only the prokaryotic community but also prokaryotic viruses. Furthermore, combining our microcosm experiments with publicly available environmental data mining, we identified both known and novel possible host-virus pairs. In particular, the growth of prokaryotes associating with phytoplanktonic organic matter, such as Bacteroidetes (Polaribacter and NS9 marine group), Vibrio spp., and Rhodobacteriales (Nereida and Planktomarina), was accompanied by an increase in viruses predicted to infect Bacteroidetes, Vibrio, and Rhodobacteriales, respectively. Collectively, our findings suggest that changes in bloom-forming species can be followed by an increase in a specific group of prokaryotes and their viruses and that elucidating these tripartite relationships among specific phytoplankton, prokaryotes, and prokaryotic viruses improves our understanding of coastal biogeochemical cycling in blooms.IMPORTANCEThe primary production during marine phytoplankton bloom and the consumption of the produced organic matter by heterotrophic prokaryotes significantly contribute to coastal biogeochemical cycles. While the activities of those heterotrophic prokaryotes are presumably affected by viral infection, the dynamics of their viruses during blooms are not fully understood. In this study, we experimentally demonstrated that intracellular fractions of taxonomically distinct bloom-forming phytoplankton species, the diatom Chaetoceros sp. and the raphidophycean alga Heterosigma akashiwo, promoted the growth of taxonomically different prokaryotes and prokaryotic viruses. Based on their dynamics and predicted hosts of those viruses, we succeeded in detecting already-known and novel possible host-virus pairs associating with either phytoplankton species. Altogether, we propose that the succession of bloom-forming phytoplankton would change the composition of the abundant prokaryotes, resulting in an increase in their viruses. These changes in viral composition, depending on bloom-forming species, would alter the dynamics and metabolism of prokaryotes, affecting biogeochemical cycling in blooms.

A lag bloom pattern of phytoplankton after freshwater input events revealed by daily samples during summer in Qinhuangdao coastal water, China.

Phytoplankton blooms have become a global concern due to their negative impacts on public health, aquaculture, tourism, and the economic stability of coastal regions. Therefore, elucidating the shifts in phytoplankton community structure and abundance, as well as their environmental drivers, is crucial. However, existing studies often fail to capture the detailed dynamics of phytoplankton blooms and their environmental triggers due to low temporal observation resolution. In this study, high temporal resolution (daily) samples were collected over 43 days to investigate the influence of environmental factors on phytoplankton in Qinhuangdao in the summer. During the observation period, a total of 45 phytoplankton species were identified, comprising 26 Bacillariophyta species, 16 Dinophyta species, 2 Euglenophyta species, and 1 Chromophyta species. Interestingly, a lag bloom pattern of phytoplankton behind freshwater input was observed across day-to-day samples. Phytoplankton blooms typically lagged 1-3 days behind periods of decreased salinity and nutrient input, suggesting that freshwater influx provides the foundational materials and benefits for these blooms. Moreover, the phytoplankton blooms were triggered by six dominant species, i.e., Chaetoceros spp., Pseudo-nitzschia delicatissima, Skeletonema costatum, Protoperdinium spp., Leptocylindrus minimus, Pseudo-nitzschia pungens, and Thalassiosira spp. Consequently, the succession of phytoplankton showed a predominant genera shift in the following sequence: Nitzschia, Protoperdinium, and Prorocentrum - Skeletonema - Pseudo-nitzschia - Gymnodinium - Leptocylindrus. Besides that, a deterministic process dominated phytoplankton community assembly across time series, and DIP is a key factor in shifting the phytoplankton community structures in this area. In summary, our study offers high-resolution observations on the succession of phytoplankton communities and sheds light on the complex and differentiated responses of phytoplankton to environmental factors. These findings enhance our understanding of the dynamics of phytoplankton blooms and their environmental drivers, which is essential for the effective management and mitigation of their adverse impacts.

Warming and trophic structure tightly control phytoplankton bloom amplitude, composition and succession.

To better identify the responses of phytoplankton blooms to warming conditions as expected in a climate change context, an in situ mesocosm experiment was carried out in a coastal Mediterranean lagoon (Thau Lagoon, South of France) in April 2018. Our objective was to assess both the direct and indirect effects of warming on phytoplankton, particularly those mediated by top-down control. Four treatments were applied: 1) natural planktonic community with ambient water temperature (C); 2) natural planktonic community at +3°C elevated temperature (T); 3) exclusion of larger zooplankton (> 200 μm; mesozooplankton) leaving microzooplankton predominant with ambient water temperature (MicroZ); and 4) exclusion of larger zooplankton (> 200 μm; mesozooplankton) at +3°C elevated temperature (TMicroZ). Warming strongly depressed the amplitude of the phytoplankton bloom as the chlorophyll a concentration was twice lower in the T treatment. This decline under warmer conditions was most likely imputed to increase top-down control by zooplankton. However, removal of mesozooplankton resulted in an opposite trend, with a higher bloom amplitude observed under warmer conditions (MicroZ vs. TMicroZ) pointing at a strong interplay between micro- and mesozooplankton and the effect of warming for the spring phytoplankton blooms. Furthermore, both warming and mesozooplankton exclusion induced shifts in phytoplankton community composition during bloom and post-bloom periods, favoring dinoflagellates and small green algae at the expense of diatoms and prymnesiophytes. Moreover, warming altered phytoplankton succession by promoting an early bloom of small green flagellates, and a late bloom of diatoms. Our findings clearly highlighted the sensitivity of phytoplankton blooms amplitudes, community composition and succession patterns to temperature increases, as well as the key role of initial zooplankton community composition to elicit opposite response in bloom dynamics. It also points out that warmer conditions might favor dinoflagellates and small green algae, irrespective of zooplankton community composition, with potential implications for food web dynamics and energy transfer efficiency under future ocean condition.

Influence of circulation processes on cyanobacteria bloom and phytoplankton succession in the Baltic Sea coastal area

Many studies related to the influence of eddies on the primary production chain of marine ecosystems have been conducted; however, this effect tends to be regionally specific, especially in coastal dynamic waters. In the Baltic Sea, mesoscale and submesoscale eddies are a ubiquitous feature of water circulation during summer, when diazotrophic cyanobacteria blooms occur in surface waters due to the excess of phosphorus in seawater. Climatic change may increase the frequency and duration of these negative events in the marine ecosystem. We examined the taxonomic composition, abundance, and primary production of phytoplankton in the southeastern Baltic Sea during the occurrence of the packed eddy system at the end of the abnormally warm summer of 2018. Massive cyanobacteria growth was observed in the plume of the eutrophic Vistula Lagoon in the Gulf of Gdansk. The only species diazotrophic Dolichospermum flos-aquae ((Bornet & Flahault) P. Wacklin, L. Hoffmann & Komárek, 2009) vegetated along the western coast of the Sambia Peninsula. Its colonies reached the highest biomass nearby the dumping site of the Amber Mining Plant in Yantarny, Kaliningrad Region, Russia. The cyanobacteria colonies dispersed in the outgoing jet of a relatively warm eddy dipole. Chrysochromulina spp. (Lackey, 1939) was dominant in these nitrogen-rich waters. In contrast, cryptophyte species dominated in the relatively cold waters of the dipole anticyclone that resulted in a fourfold decline in primary production. The decrease in the number of mobile phytoplankton species was revealed within the “old” eddies near the northern coast of the Sambia Peninsula and the Curonian Spit. Meanwhile, species of the spring–autumn complex Coscinodiscus granii (Gough, 1905), Peridiniella catenate ((Levander) Balech, 1977) and other developed in the community. This implies that the appearance of eddies can cause phytoplankton succession in the coastal area. The mechanism of their influence was similar to the action of other physical factors perturbing a relatively stationary environment. Capture of cyanobacterial colonies by eddies led to an improvement of the ecological situation in the area, as cyanobacteria transported their biomass outside the coastal area. However, the opposite direction processes obviously were the deterioration of light conditions, increased water turbidity, and organic matter concentration.

Spatial and temporal patterns of phytoplankton community succession and characteristics of realized niches in Lake Taihu, China

Understanding the dynamics and succession of phytoplankton in large lakes can help inform future lake management. The study analyzed phytoplankton community variations in Lake Taihu over a 21-year period, focusing on realized niches and their impact on succession. The study developed a niche periodic table with 32 niches, revealing responses to environmental factors and the optimal number of niches. Results showed that the phytoplankton in Lake Taihu showed significant spatial and temporal heterogeneity, with biomass decreasing as one moved from the northwest to the southeast and expanding towards central lake area, and towards autumn and winter. Different phytoplankton groups in Lake Taihu occupied realized niches shaped by temperature, nitrate, and phosphate. To predict the response of eutrophic freshwater lake ecosystems to human activities and climate change, it is critical to interpret the law of phytoplankton bloom and niche succession.

Fall-winter sea surface temperature anomalies affect subsequent spring-summer phytoplankton succession and bioluminescence patterns in the Black Sea coastal waters near Crimea

Seasonal and interannual dynamics of bioluminescence intensity and succession of the major phytoplankton taxonomic groups were analyzed using the six-year monitoring of Crimean coastal waters (the northern Black Sea) in 2009–2014. Monitoring program included regular CTD and bioluminescence intensity casts in the upper 60 m layer by means of “Salpa-M” sonde accompanied with phytoplankton sampling from subsurface (∼0.2 m) and from the layer of maximal bioluminescence intensity. Years with anomalous warm and cold preceding fall-winter periods were defined on the basis of remotely sensed monthly sea surface temperature (SST) and long-term records on coastal SST measuring station. It was shown that succession of phytoplankton and net vertical bioluminescence patterns in subsequent spring-summer seasons depend upon the SST anomaly during preceding fall-winter period. In “cold” years a minimal bioluminescence intensity associated with a diminished biomass and species abundance of luminous dinoflagellates as well as diatoms and dinoflagellates groups as a whole were observed. A number of luminous dinoflagellate species dropped out of spring phytoplankton community (e.g., Scrippsiella cf. acuminata). As a result, a typical spring peak of bioluminescence in the upper mixed layer has not been observed during these years. In contrast maximal bioluminescence intensity and phytoplankton abundance in spring-summer was observed in “warm” years; biomass and bioluminescence intensity peaks shift to earlier month (April) in comparison to “moderate” years; period of dinoflagellate dominance was more extended during the spring-summer succession phase. Overall, group of dinoflagellates including luminous species, seems to be the most sensitive group of algae to climatic SST anomalies in coastal waters of the northern Black Sea. Hence, the bioluminescence in the upper sea layer can act as an indicator of climate-induced phytoplankton community restructuring.

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.

Lake sediment DNA reveals the response of phytoplankton to warming

Phytoplankton can be used as an indicator of aquatic ecological health and to monitor nutrient levels, which are the basis of formulating lake management strategies. However, long-term phytoplankton succession and their response to environmental changes remain poorly understood due to the paucity of ecological monitoring data and the limitation of the traditional paleolimnological indicators used to identify non-fossilized phytoplankton groups (e.g. Cyanobacteria). In this study, we used both paleolimnological and 23S rRNA gene metabarcoding analyses of phytoplankton (eukaryotic algae and cyanobacteria) to probe the impacts of environmental changes on the phytoplankton dynamics over the past millennium in this deep, fault-bounded, eutrophic Lake Chenghai on the Yunnan–Kweichow Plateau, southwest China. The phytoplankton community succession was observed in four periods, including the Medieval Warm Periods (1000s–1400s), the Little Ice Age (1400s–1800s), the early Current Warm Period (1800s–1950s) and the Anthropocene (1950s–present). Specifically, Cyanobacteria dominated during the warm periods, whereas Chlorophyta was abundant during the cold period. Bloom-forming or cyanotoxin-producing taxa (e.g., Aphanizomenon) have mainly occurred in recent decades. Co-occurrence network analysis indicated that the community structure became complex and that the diversity has increased markedly during the Anthropocene. Multiple statistical analyses demonstrated that temperature was a key driver controlling phytoplankton succession on the decadal time scales and that anthropogenic warming may have led to an increase in the relative abundance of bloom-forming cyanobacterial taxa in recent decades. These findings further suggest that any efforts to reduce nutrients—and the effects of these efforts—will be offset, and that cyanobacterial blooms may continue to increase in Lake Chenghai if anthropogenic warming conditions continue.

From lipophilic to hydrophilic toxin producers: Phytoplankton succession driven by an atmospheric river in western Patagonia

Phytoplankton succession is related to hydroclimatic conditions. In this study we provide the first description of a toxic phytoplankton succession in the Patagonian Fjord System. The shift was modulated by atmospheric-oceanographic forcing and consisted of the replacement of the marine dinoflagellate Dinophysis acuta in a highly stratified water column during austral summer by the diatom Pseudo-nitzschia calliantha in a mixed water column during late summer and early autumn. This transition, accompanied by a change in the biotoxin profiles (from lipophilic dinophysis toxins to hydrophilic domoic acid), was induced by the arrival of an intense atmospheric river. The winds in Magdalena Sound may have been further amplified, due to its west-east orientation and its location within a tall, narrow mountain canyon. This work also documents the first known appearance of toxic P. calliantha in Northern Patagonian. The potential impacts of the biotoxins of this species on higher trophic levels are discussed.

Functional and structural responses of plankton communities toward consecutive experimental heatwaves in Mediterranean coastal waters

The frequency of marine heatwaves (HWs) is projected to increase in the Mediterranean Sea over the next decades. An in situ mesocosm experiment was performed in a Mediterranean lagoon for 33 days. Three mesocosms were used as controls following the natural temperature of the lagoon. In three others, two HWs of + 5 °C compared to the controls were applied from experimental day (d) 1 to d5 (HW1) and from d11 to d15 (HW2). High-frequency data of oxygen, chlorophyll-a (chl-a), temperature, salinity and light from sensors immersed in all mesocosms were used to calculate gross primary production (GPP), respiration (R) and phytoplankton growth (µ) and loss (L) rates. Nutrients and phytoplankton community structure from pigments were also analyzed. HW1 significantly increased GPP, R, chl-a, µ and L by 7 to 38%. HW2 shifted the system toward heterotrophy by only enhancing R. Thus, the effects of the first HW resulted in the attenuation of those of a second HW on phytoplankton processes, but not on community respiration, which was strongly regulated by temperature. In addition, natural phytoplankton succession from diatoms to haptophytes was altered by both HWs as cyanobacteria and chlorophytes were favored at the expense of haptophytes. These results indicate that HWs have pronounced effects on Mediterranean plankton communities.

Unusual red tide of the dinoflagellate Lingulodinium polyedra during an upwelling event off the Algarve coast (SW Iberia)

Low biomass, but highly toxic algal blooms are frequent in the Ria Formosa coastal lagoon and adjacent coastal zone (southern Portugal), usually associated with specific oceanographic and nutrient conditions. In June 2019, a massive bloom of the dinoflagellate Lingulodinium polyedra developed along the coast, causing water discolouration, and the closure of beaches and of bivalve harvesting, with significant socioeconomic consequences. This study aims to evaluate the relationships between phytoplankton composition and environmental conditions before, during, and after the L. polyedra bloom. Water samples were collected in the Ria Formosa coastal lagoon throughout June and July 2019 for determination of nutrient and chlorophyll-a concentration using spectrophotometric methods. Phytoplankton composition and abundance were evaluated using inverted microscopy. Upwelling intensity was estimated considering a wind-based index, the cross-shore Ekman transport. Results show strong relationships between phytoplankton community composition and nutrients, particularly a positive relationship between centric diatoms and nitrogen, and a negative relationship between several dinoflagellate genera, and phosphorus and silicon. L. polyedra was not significantly associated with any nutrient variable, most likely due to its mixotrophic capabilities. A clear phytoplankton succession, typical of eastern boundary upwelling locations, was observed throughout the different bloom phases, from dominance of type II dinoflagellates (Heterocapsa, Prorocentrum) in the pre-bloom period, to dominance of L. polyedra (type V) during the bloom, and finally dominance of centric diatoms in the post-bloom period. However, the L. polyedra bloom was not associated with upwelling relaxation, but rather with an active upwelling event.

Interaction among spring phytoplankton succession, water discharge patterns, and hydrogen peroxide dynamics in the Caloosahatchee River in southwest Florida

Phytoplankton communities are major primary producers in the aquatic realm and are responsible for shaping aquatic ecosystems. The dynamics of algal blooms could be determined by a succession of variable taxonomic groups, which are altered based on complex environmental factors such as nutrient availability and hydraulic factors. In-river structures potentially increase the occurrence of harmful algal blooms (HABs) by increasing water residence time and deteriorating water quality. How flowing water stimulates cell growth and affects the population dynamics of phytoplankton communities is a prioritized question that needs to be addressed for water management tactics. The goal of this study was to determine if an interaction between water flow and water chemistry is present, furthermore, to determine the relationship among phytoplankton community successions in the Caloosahatchee River, a subtropical river strongly influenced by human-controlled water discharge patterns from Lake Okeechobee. Particularly we focused on how phytoplankton community shifts influence the natural abundance of hydrogen peroxide, the most stable reactive oxygen species and a byproduct of oxidative photosynthesis. High-throughput amplicon sequencing using universal primers amplify 23S rRNA gene in cyanobacteria and eukaryotic algal plastids revealed that Synechococcus and Cyanobium were the dominant cyanobacterial genera and their relative abundance ranged between 19.5 and 95.3% of the whole community throughout the monitoring period. Their relative abundance declined when the water discharge increased. On the contrary, the relative abundance of eukaryotic algae sharply increased after water discharge increased. As water temperature increased in May, initially dominant Dolichospermum decreased as Microcystis increased. When Microcystis declined other filamentous cyanobacteria such as Geitlerinema, Pseudanabaena, and Prochlorothreix increased in their relative abundances. Interestingly, a peak of extracellular hydrogen peroxide was observed when Dolichospermum dominance was ended, and M. aeruginosa numbers increased. Overall, phytoplankton communities were strongly impacted by human-induced water discharge patterns.

Viruses may facilitate the cyanobacterial blooming during summer bloom succession in Xiangxi Bay of Three Gorges Reservoir, China.

The occurrence of cyanobacterial blooms in summer are frequently accompanied by the succession of phytoplankton communities in freshwater. However, little is known regarding the roles of viruses in the succession, such as in huge reservoirs. Here, we investigated the viral infection characteristics of phytoplankton and bacterioplankton during the summer bloom succession in Xiangxi Bay of Three Gorges Reservoir, China. The results indicated that three distinct bloom stages and two successions were observed. From cyanobacteria and diatom codominance to cyanobacteria dominance, the first succession involved different phyla and led to a Microcystis bloom. From Microcystis dominance to Microcystis and Anabaena codominance, the second succession was different Cyanophyta genera and resulted in the persistence of cyanobacterial bloom. The structural equation model (SEM) showed that the virus had positive influence on the phytoplankton community. Through the Spearman's correlation and redundancy analysis (RDA), we speculated that both the increase of viral lysis in the eukaryotic community and the increase of lysogeny in cyanobacteria may contributed to the first succession and Microcystis blooms. In addition, the nutrients supplied by the lysis of bacterioplankton might benefit the second succession of different cyanobacterial genera and sustain the dominance of cyanobacteria. Based on hierarchical partitioning method, the viral variables still have a marked effect on the dynamics of phytoplankton community, although the environmental attributes were the major factors. Our findings suggested that viruses played multiple potential roles in summer bloom succession and may help the blooms success of cyanobacteria in Xiangxi Bay. Under the background of increasingly serious cyanobacterial blooms worldwide, our study may have great ecological and environmental significance for understanding the population succession in phytoplankton and controlling the cyanobacterial blooms.