Harmful Blooms Research Articles

River phosphorus cycling during high flow may constrain Lake Erie cyanobacteria blooms

Cyanobacterial harmful blooms have been increasing worldwide, due in part to excessive phosphorus (P) losses from agriculture-dominated watersheds. Unfortunately, cyanobacteria bloom management is often complicated by uncertainty associated with river P cycling. River P cycling mediates P exports during low flow but has been assumed to be unimportant during high flows. Thus, we examined interactions between dissolved reactive phosphorus (DRP) and suspended sediment P during high flows in the Maumee River network, focusing on March–June Maumee River DRP exports, which fuel recurring cyanobacteria blooms in Lake Erie. We estimate that during 2003–2019 March to June high flow events, P sorption reduced DRP exports by an average of 13–27%, depending upon the colloidal-P:DRP ratio, decreasing the bioavailability of P exports, and potentially constraining cyanobacteria blooms by 13–40%. Phosphorus sorption was likely lower during 2003–2019 than 1975–2002 due to reductions in suspended sediment loads, associated with soil-erosion-minimizing agricultural practices. This unintended outcome of erosion management has likely decreased P sorption, increased DRP exports to Lake Erie, and subsequent cyanobacteria blooms. In other watersheds, DRP–sediment P interactions during high flow could have a positive or negative effect on DRP exports; therefore, P management should consider riverine P cycles, particularly during high flow events, to avoid undermining expensive P mitigation efforts.

Uptake of Phytoplankton-Derived Carbon and Cobalamins by Novel Acidobacteria Genera in Microcystis Blooms Inferred from Metagenomic and Metatranscriptomic Evidence.

Interactions between bacteria and phytoplankton can influence primary production, community composition, and algal bloom development. However, these interactions are poorly described for many consortia, particularly for freshwater bloom-forming cyanobacteria. Here, we assessed the gene content and expression of two uncultivated Acidobacteria from Lake Erie Microcystis blooms. These organisms were targeted because they were previously identified as important catalase producers in Microcystis blooms, suggesting that they protect Microcystis from H2O2. Metatranscriptomics revealed that both Acidobacteria transcribed genes for uptake of organic compounds that are known cyanobacterial products and exudates, including lactate, glycolate, amino acids, peptides, and cobalamins. Expressed genes for amino acid metabolism and peptide transport and degradation suggest that use of amino acids and peptides by Acidobacteria may regenerate nitrogen for cyanobacteria and other organisms. The Acidobacteria genomes lacked genes for biosynthesis of cobalamins but expressed genes for its transport and remodeling. This indicates that the Acidobacteria obtained cobalamins externally, potentially from Microcystis, which has a complete gene repertoire for pseudocobalamin biosynthesis; expressed them in field samples; and produced pseudocobalamin in axenic culture. Both Acidobacteria were detected in Microcystis blooms worldwide. Together, the data support the hypotheses that uncultured and previously unidentified Acidobacteria taxa exchange metabolites with phytoplankton during harmful cyanobacterial blooms and influence nitrogen available to phytoplankton. Thus, novel Acidobacteria may play a role in cyanobacterial physiology and bloom development. IMPORTANCE Interactions between heterotrophic bacteria and phytoplankton influence competition and successions between phytoplankton taxa, thereby influencing ecosystem-wide processes such as carbon cycling and algal bloom development. The cyanobacterium Microcystis forms harmful blooms in freshwaters worldwide and grows in buoyant colonies that harbor other bacteria in their phycospheres. Bacteria in the phycosphere and in the surrounding community likely influence Microcystis physiology and ecology and thus the development of freshwater harmful cyanobacterial blooms. However, the impacts and mechanisms of interaction between bacteria and Microcystis are not fully understood. This study explores the mechanisms of interaction between Microcystis and uncultured members of its phycosphere in situ with population genome resolution to investigate the cooccurrence of Microcystis and freshwater Acidobacteria in blooms worldwide.

Biphasic effects of typical chlorinated organophosphorus flame retardants on Microcystis aeruginosa

The potential accumulation of chlorinated organophosphorus flame retardants (Cl-OPFRs) in aquatic environments sparked interest in studying the effects of Cl-OPFRs on cyanobacterial blooms. In this work, two common Cl-OPFRs, tris(1,3-dichloro-2-propyl) phosphate (TDCPP) and tris(2-chloroethyl) phosphate (TCEP), induced dose-dependent biphasic effect on bloom-forming M. aeruginosa. The hormetic response to low-dose Cl-OPFRs was associated with the upregulation of the type I NADH dehydrogenase (NDH-1) complex and its mediated cyclic electron transfer (CET) pathway, as reflected by a transient post-illumination increase in chlorophyll fluorescence, the dark reduction of P700+ and the change of NDH-1-related gene expression. The increased CET activity and carotenoid content jointly reduced the intracellular ROS production, facilitating cyanobacterial growth. Conversely, a higher concentration of both Cl-OPFRs induced severe inhibition of growth and photosynthetic oxygen-evolving activity through an imbalance between PSII and PSI. Toxic-dose Cl-OPFRs inhibited state transition and fixed cells into the State I with a higher PSII/PSI ratio, as indicated by chlorophyll fluorescence induction, 77 K fluorescence emission spectra and photosystem stoichiometry. The elevated PSII/PSI ratio created an imbalance between the two photosystems and eventually lead to ROS overproduction, which generate adverse effects on cell growth. This work provides important insights into the hormetic mechanism of Cl-OPFRs on Microcystis aeruginosa and their potential roles in harmful cyanobacteria blooms.

Acetylacetone Interferes with Carbon and Nitrogen Metabolism of Microcystis aeruginosa by Cutting Off the Electron Flow to Ferredoxin.

The regulation of photosynthetic machinery with a nonoxidative approach is a powerful but challenging strategy for the selective inhibition of bloom-forming cyanobacteria. Acetylacetone (AA) was recently found to be a target-selective cyanocide for Microcystis aeruginosa, but the cause and effect in the studied system are still unclear. By recording of the chemical fingerprints of the cells at two treatment intervals (12 and 72 h with 0.1 mM AA) with omics assays, the molecular mechanism of AA in inactivating Microcystis aeruginosa was elucidated. The results clearly reveal the effect of AA on ferredoxin and the consequent effects on the physiological and biochemical processes of Microcystis aeruginosa. In addition to its role as an electron acceptor of photosystem I, ferredoxin plays pivotal roles in the assimilation of nitrogen in cyanobacterial cells. The effect of AA on ferredoxin and on nonheme iron of photosystem II first cut off the photosynthetic electron transfer flow and then interrupted the synthesis of adenosine triphosphate (ATP) and reduced nicotinamide adenine dinucleotide phosphate (NADPH), which ultimately might affect carbon fixation and nitrogen assimilation metabolisms. The results here provide missing pieces in the current knowledge on the selective inhibition of cyanobacteria, which should shed light on the better control of harmful blooms.

Dynamic Phycobilin Pigment Variations in Diazotrophic and Non-diazotrophic Cyanobacteria Batch Cultures Under Different Initial Nitrogen Concentrations.

Increased anthropogenic nutrient loading has led to eutrophication of aquatic ecosystems, which is the major cause of harmful cyanobacteria blooms. Element stoichiometry of cyanobacteria bloom is subject to nutrient availabilities and may significantly contribute to primary production and biogeochemical cycling. Phycobilisome is the antenna of the photosynthetic pigment apparatus in cyanobacteria, which contains phycobilin pigments (PBPs) and linker proteins. This nitrogen (N)-rich protein complex has the potential to support growth as a N-storage site and may play a major role in the variability of cyanobacteria N stoichiometry. However, the regulation of PBPs during bloom formation remains unclear. We investigated the temporal variation of N allocation into PBPs and element stoichiometry for two ubiquitous cyanobacteria species, Microcystis aeruginosa and Dolichospermum flos-aquae, in a batch culture experiment with different initial N availabilities. Our results indicated that the N allocation into PBPs is species-dependent and tightly regulated by the availability of nutrients fueling population expansion. During the batch culture experiment, different nutrient uptake rates led to distinct stoichiometric imbalances of N and phosphorus (P), which substantially altered cyanobacteria C: N and C: P stoichiometry. Microcystis invested cellular N into PBPs and exhibited greater flexibility in C: N and C: P stoichiometry than D. flos-aquae. The dynamics of such N-rich macromolecules may help explain the N stoichiometry variation during a bloom and the interspecific difference between M. aeruginosa and D. flos-aquae. Our study provides a quantitative understanding of the elemental stoichiometry and the regulation of PBPs for non-diazotrophic and diazotrophic cyanobacteria blooms.

Potential Use of Aquatic Vascular Plants to Control Cyanobacterial Blooms: A Review

Intense “blooming” of cyanobacteria (blue-green algae) caused by eutrophication and climate change poses a serious threat to freshwater ecosystems and drinking water safety. Preventing the proliferation of cyanobacteria and reducing water nutrient load is a priority for the restoration of eutrophic water bodies. Aquatic plants play an important role in the function and structure of aquatic ecosystems, affecting the physiochemistry of the water and bottom sediments, primary production, and biotic interactions that support a balanced ecosystem. This review examines the inhibitory effect of aquatic vascular plants on harmful blooms of cyanobacteria. Aquatic plants are able to successfully inhibit the growth of cyanobacteria through various mechanisms, including by reducing nutrient and light availability, creating favorable conditions for the development of herbivorous zooplankton, and releasing allelopathic active substances (allelochemicals) with algicidal effect. Allelopathy is species-specific and therefore acts as one of the key mechanisms by which the development of cyanobacterial populations in aquatic ecosystems is regulated. However, allelopathic activity of aquatic vascular plants depends on various factors (species characteristics of aquatic plants, area, and density of overgrowth of water bodies, physiochemical properties of allelopathically active substances, hydrological and hydrochemical regimes, temperature, light intensity, etc.), which may regulate the impact of allelochemicals on algal communities. The paper also discusses some problematic aspects of using fast-growing species of aquatic vascular plants to control cyanobacterial blooms.

Variability patterns and phenology of harmful phytoplankton blooms off southern Portugal: Looking for region-specific environmental drivers and predictors

Harmful algal blooms (HABs) negatively impact coastal ecosystems, fisheries, and human health, and their prediction has become imperative for effective coastal management. This study aimed to evaluate spatial-temporal variability patterns and phenology for key toxigenic phytoplankton species off southern Portugal, during a 6-year period, and identify region-specific environmental drivers and predictors. Total abundance of species responsible for amnesic shellfish poisoning (Pseudo-nitzschia spp.), diarrhetic shellfish poisoning (Dinophysis spp.), and paralytic shellfish poisoning (G. catenatum) were retrieved, from the National Bivalve Mollusk Monitoring System public database. Contemporaneous environmental variables were acquired from satellite remote sensing, model-derived data, and in situ observations, and generalized additive models (GAMs) were used to explore the functional relationships between HABs and environmental variables and identify region-specific predictors. Pseudo-nitzschia spp. showed a bimodal annual cycle for most coastal production areas, with spring and summer maxima, reflecting the increase in light intensity during the mixed layer shoaling stage, and the later stimulatory effects of upwelling events, with a higher bloom frequency over coastal areas subjected to stronger upwelling intensity. Dinophysis spp. exhibited a unimodal annual cycle, with spring/summer maxima associated with stratified conditions, that typically promote dinoflagellates. Dinophysis spp. blooms were delayed with respect to Pseudo-nitzschia spp. spring blooms, and followed by Pseudo-nitzschia spp. summer blooms, probably reflecting upwelling-relaxation cycles. G. catenatum occurred occasionally, namely in areas more influenced by river discharges, under weaker upwelling. Statistical-empirical models (GAMs) explained 7-8%, and 21−54% of the variability in Pseudo-nitzschia spp. and Dinophysis spp., respectively. Overall, a set of four easily accessible environmental variables, surface photosynthetically available radiation, mixed layer depth, sea surface temperature, and chlorophyll-a concentration, emerged as the most influential predictors. Additionally, over the coastal production areas along the south coast, river discharges exerted minor negative effects on both HAB groups. Despite evidence supporting the role of upwelling intensity as an environmental driver of Pseudo-nitzschia spp., it was not identified as a relevant model predictor. Future model developments, such as the inclusion of additional environmental variables, and the implementation of species- and period-specific, and hybrid modelling approaches, may further support HAB operational forecasting and managing over complex coastal domains.

Ecotoxicological effects of total flavonoids in Cirsium japonicum DC on Microcystis aeruginosa

Abstract In recent years, the use of biological methods to control water bloom has become an ecological approach. In this research, the effect of total flavonoids extracted by ethanol in Cirsium japonicum DC seeds on Microcystis aeruginosa cell density and morphological changes was assessed via six treatments (0, 10, 20, 30, 40, and 50 mg/L). Chlorophyll a, carotenoid, phycocyanin (PC), and allophycocyanin (APC) content were analyzed. Also, adversity indicators variance including malondialdehyde (MDA), O2−., and antioxidant isozyme activity of superoxide dismutase (SOD) and ascorbate oxidase (APX) were revealed. The results showed M. aeruginosa density was significantly influenced by C. japonicum DC total flavonoids in a negative dose-response. After 9 days of treatment, density decreased by 58.8%, and algal cells shrank severely under treatment of 50 mg/L total flavonoids. In addition, the chlorophyll a, carotenoid and PC content displayed a decreasing trend compared to the control, meanwhile contents of MDA, APC (except 50 mg/L treatment), activity of O2−., SOD and APX increased. This study shows the total flavonoids of C. japonicum DC has higher biological activities and can interfere with growth of M. aeruginosa. It was concluded that C. japonicum DC may be useful to control harmful water bloom.

Investigating immune responses to Harmful Algal Bloom cyanotoxins in protection of human health and the environment

Abstract Harmful algal blooms (HABs) are a major environmental and public health concern globally that impact multiple essential areas including agriculture, drinking water, and recreational water. Although harmful blooms are caused by other organisms, those from cyanobacteria are the most common freshwater pollutant. Cyanobacteria produce secondary metabolites including cyanotoxins that pollute drinking and recreational waters and produce metabolites and cell components that can contribute to skin irritation. The aim of this study is to elucidate the specific mechanisms that lead to inflammation and irritation caused by exposure to these toxins. Multiplexing technology afforded the ability to investigate a variety of human cytokines and chemokines, and soluble receptors to measure immune responses in a single sample. 3D human tissue cultures were exposed to a variety of different toxins found in HABs. These samples were then examined using Luminex™ xMAP technology to look at 38 different cytokines/chemokines and 14 soluble receptors in each sample. We observed the expression of several cytokines/chemokines that regulate the inflammatory process in endothelial and epithelial cells and play a role in the recruitment of neutrophils to the site of inflammation. This could contribute to the rashes or skin irritation commonly reported by patients exposed to HABs. Additional observations and analyses are needed to identify the specific immune response pathways activated during exposure to these toxins. These findings could lead to a better understand of human exposure to cyanotoxins and more appropriate and effective treatment modalities for patients who exhibit rashes or skin irritations after being exposed to these blooms. This work is supported by the United States Environmental Protection Agency.

Climate Change‐Legacy Phosphorus Synergy Hinders Lake Response to Aggressive Water Policy Targets

AbstractWith mounting scientific evidence demonstrating adverse global climate change (GCC) impacts to water quality, water quality policies, such as the Total Maximum Daily Loads (TMDLs) under the U.S. Clean Water Act, have begun accounting for GCC effects in setting nutrient load‐reduction policy targets. These targets generally require nutrient reductions for attaining prescribed water quality standards (WQS) by setting safe levels of nutrient concentrations that curtail potentially harmful cyanobacteria blooms (CyanoHABs). While some governments require WQS to consider climate change, few tools are available to model the complex interactions between climate change and benthic legacy nutrients. We present a novel process‐based integrated assessment model (IAM) that examines the extent to which synergistic relationships between GCC and legacy Phosphorus release could compromise the ability of water quality policies to attain established WQS. The IAM is calibrated for simulating the eutrophic Missisquoi Bay and watershed in Lake Champlain (2001–2050). Water quality impacts of seven P‐reduction scenarios, including the 64.3% reduction specified under the current TMDL, were examined under 17 GCC scenarios. The TMDL WQS of 0.025 mg/L total phosphorus is unlikely to be met by 2035 under the mandated 64.3% reduction for all GCC scenarios. IAM simulations show that the frequency and severity of summer CyanoHABs increased or minimally decreased under most climate and nutrient reduction scenarios. By harnessing IAMs that couple complex process‐based simulation models, the management of water quality in freshwater lakes can become more adaptive through explicit accounting of GCC effects on both the external and internal sources of nutrients.

Emergent marine toxins risk assessment using molecular and chemical approaches.

Cyanobacteria harmful blooms represent a deviation to the normal equilibrium in planktonic communities involving a rapid and uncontrolled growth. Owing to the capacity to produce toxins as secondary metabolites, cyanobacteria may cause huge economic losses in the fishing and aquaculture industries and poisoning incidents to humans due to their accumulation in the food chain. The conditions which promote toxic blooms have not yet been fully understood, but climate change and anthropogenic intervention are pointed as significant factors. For the detection of toxins in edible marine organisms, the establishment of international regulations and compulsory surveillance has been probed as exceptionally effective. However, not regulation nor monitoring have been settled concerning emergent marine toxins. In the light of this scenario, it becomes essential to apply fast and reliable surveillance methodologies for the early detection of cyanobacterial blooms as well as the occurrence of emergent marine toxins. Shotgun metagenomic sequencing has potential to become a powerful diagnostic tool in the fields of food safety and One Health surveillance. This culture‐independent approach overcomes limitations of traditional microbiological techniques; it allows a quick and accurate assessment of a complex microbial community, including quantitative identification and functional characterisation, in a single experiment. In the framework of the EU‐FORA fellowship, with the final goal of evaluate metagenomics as a promising risk assessment tool, the fellow worked on the development of an innovative workflow through state‐of‐the‐art molecular and chemical analytical procedures. This work programme aims to evaluate the occurrence of emergent marine toxins and the producing organisms in Cabo Verde coastal cyanobacteria blooms. Our results show the outstanding potential of a holistic metagenomic approach for the risk assessment of emergent marine toxins and the producing organisms. Additionally, we have also highlighted its value for the identification and evaluation of secondary metabolites as natural bioactive compounds with biotechnological and industrial interest.

Rylene Dye-Loaded Polymeric Nanoparticles for Photothermal Eradication of Harmful Dinoflagellates, Akashiwo sanguinea and Alexandrium pacificum.

In the era of climate changes, harmful dinoflagellate outbreaks that produce potent algal toxins, odor, and water discoloration in aquatic environments have been increasingly reported. Thus, various treatments have been attempted for the mitigation and management of harmful blooms. Here, we report engineered nanoparticles that consist of two different types of rylene derivatives encapsulated in polymeric micelles. In addition, to avoid dissociation of the aggregate, the core of micelle was stabilized via semi-interpenetrating network (sIPN) formation. On two types of the marine red-tide dinoflagellates, Akashiwo sanguinea and Alexandrium pacificum, the nanoparticle uptake followed by fluorescence labeling and photothermal effect was conducted. Firstly, fluorescence microscopy enabled imaging of the dinoflagellates with the ultraviolet chromophore, Lumogen Violet. Lastly, near-infrared (NIR) laser irradiation was exposed on the Lumogen IR788 nanoparticle-treated Ak. Sanguinea. The irradiation resulted in reduced cell survival due to the photothermal effect in microalgae. The results suggested that the nanoparticle, IR788-sIPN, can be applied for potential red-tide algal elimination.

Modeling the life cycle of four types of phytoplankton and their bloom mechanisms in a benthic-pelagic coupled ecosystem

Harmful diatom (Coscinodiscus waillesi and Eucampia zodiacus) blooms frequently occur in the western coastal area of Japan from late autumn to early spring, causing discoloration of edible seaweed nori (Pyropia yezoensis). One of the causes of the discoloration is thought to be nutrient depletion (oligotrophication) due to nutrient uptake by diatoms. The goal of our study was to elucidate the mechanisms underlying phytoplankton blooms and the effects of such blooms on comprehensive nutrient cycles in the benthic-pelagic ecosystem. We developed a new ecosystem model, EMAGIN-L.P., simultaneously representing phytoplankton life cycle and the benthic-pelagic ecosystem. The life cycles of four types of phytoplankton—dinoflagellates (DFL), small diatoms (SDA), Coscinodiscus wailesii (CDW), and Eucampia zodiacus (EZ)—were numerically modeled and incorporated into an existing ecosystem model, ECOHYM (Sohma et al., 2008a), representing the food web among the benthic and pelagic systems and carbon-nitrogen-phosphorus-oxygen-coupled cycles driven by biogeochemical and physical processes. The model was applied to the Harima-Nada Sea where the discoloration of nori frequently occurs. The model reproduced the differences in timing and scale of the four phytoplankton blooms, and each bloom could be explained by a combination of temperature suitability, light availability, nutrient limitation, and vertical mixing within the water column. Furthermore, through a sensitivity analysis, competition for nutrient uptake among different types of phytoplankton was observed in the model. That is, from June to October, when DFL and SDA blooms occur, the SDA nutrient uptake rate is high and SDA suppresses the DFL bloom, while from November to March, when CDW and EZ blooms occur, the nutrient uptake rate of EZ is high and the CDW bloom is slightly suppressed. The developed model representing the phytoplankton bloom mechanisms in the whole benthic-pelagic coupled ecosystem will be a useful tool for revealing the mechanisms underlying the nutrient cycle and the contribution of harmful diatom blooms to the discoloration of nori. The modeling approach presented in this paper (i.e., categorizing different types of major phytoplankton and incorporating their life cycle into the entire benthic-pelagic coupling ecosystem) can be an effective method to understand, predict, and manage the problems caused by harmful diatom blooms across different damage types, harmful diatom species, and ocean areas.

Development of a Risk Characterization Tool for Harmful Cyanobacteria Blooms on the Ohio River.

A data-driven approach to characterizing the risk of cyanobacteria-based harmful algal blooms (cyanoHABs) was undertaken for the Ohio River. Twenty-five years of river discharge data were used to develop Bayesian regression models that are currently applicable to 20 sites spread-out along the entire 1579 km of the river’s length. Two site-level prediction models were developed based on the antecedent flow conditions of the two blooms that occurred on the river in 2015 and 2019: one predicts if the current year will have a bloom (the occurrence model), and another predicts bloom persistence (the persistence model). Predictors for both models were based on time-lagged average flow exceedances and a site’s characteristic residence time under low flow conditions. Model results are presented in terms of probabilities of occurrence or persistence with uncertainty. Although the occurrence of the 2019 bloom was well predicted with the modeling approach, the limited number of events constrained formal model validation. However, as a measure of performance, leave-one-out cross validation returned low misclassification rates, suggesting that future years with flow time series like the previous bloom years will be correctly predicted and characterized for persistence potential. The prediction probabilities are served in real time as a component of a risk characterization tool/web application. In addition to presenting the model’s results, the tool was designed with visualization options for studying water quality trends among eight river sites currently collecting data that could be associated with or indicative of bloom conditions. The tool is made accessible to river water quality professionals to support risk communication to stakeholders, as well as serving as a real-time water data monitoring utility.

Removal of microcystin (MC-LR) in constructed wetlands integrated with microbial fuel cells: Efficiency, bioelectricity generation and microbial response

Microcystins (MCs) pollution caused by cyanobacteria harmful blooms (CHBs) has posed short- and long-term risks to aquatic ecosystems and public health. Constructed wetlands (CWs) have been verified as an effective technology for eutrophication but the removal performance for MCs did not achieve an acceptable level. CWs integrated with microbial fuel cell (MFC-CWs) were developed to intensify the nutrient and Microcystin-LR (MC-LR) removal efficiencies in this study. The results indicated that closed-circuit MFC-CWs (T1) exhibited a better NO3−-N, NH4+-N, TP and MC-LR removal efficiency compared to that of open-circuit MFC-CWs (CK, i.e., traditional CWs). Therein, a MC-LR removal efficiency of greater than 95% was observed in both trials in T1. The addition of sponge iron to the anode layer of MFC-CWs (T2) improved only the NO3−-N removal and efficiency bioelectricity generation performance compared to T1, and the average effluent MC-LR concentration of T2 (1.14 μg/L) was still higher than the provisional limit concentration (1.0 μg/L). The microbial community diversity of T1 and T2 was simplified compared to CK. The relative abundance of Sphingomonadaceae possessing the degradation capability for MCs increased in T1, which contributed to the higher MC-LR removal efficiency compared to CK and T2. While the relative abundance of electrochemically active bacteria (EAB) (i.e., Desulfuromonadaceae and Desulfomicrobiaceae) in the anode of T2 was promoted by the addition of sponge iron. Overall, this study suggests that integrating MFC into CWs provides a feasible intensification strategy for eutrophication and MCs pollution control.

Long-term phosphorus reduction and phytoplankton responses in an urban lake (USA)

Eutrophication is one of the primary factors causing harmful cyanobacteria blooms in freshwater lakes. This study investigated the long-term changes in water quality and summer phytoplankton assemblages in Oswego Lake, OR, USA, in relation to phosphorus reduction through hypolimnetic aeration and alum applications. Both water quality and phytoplankton assemblages were sampled biweekly during the summers from 2001 to 2013. The concentrations of total phosphorus, soluble reactive phosphorus, and total nitrogen decreased 66%, 93% and 31%, respectively, in response to the hypolimnetic aeration and alum treatments since 2005. Summer phytoplankton assemblages showed a 62% reduction of cyanobacteria biovolume and a shift from cyanobacteria dominance (2001–2005) to diatom and chlorophyte dominance (2006–2013). Cluster analysis identified four statistically different groups of summer phytoplankton assemblages (denoted Groups 1–4). Nonmetric multidimensional scaling analysis indicated that the four groups were associated with different water quality conditions. Group 1 occurred prior to hypolimnetic aeration and was primarily comprised of cyanobacteria, associated with water conditions of high nutrients and high primary production. Group 2, dominated by cyanobacteria and chlorophytes, occurred between hypolimnetic aeration and alum surface application. Group 3 was dominated by diatoms and occurred after alum surface application. Group 4 included R-strategist phytoplankton that quickly respond to environmental changes and occurred in the years following alum injection, drawdown, and inflow alum treatment. Both Group 3 and 4 were associated with reduced nutrients in the lake. We conclude that these lake management practices had strong effects on both production and community compositions of phytoplankton, and advocate for future studies on large-scale climate impacts on lake ecosystems and to identify corresponding best management practices.

Long-Term Ammonia Toxicity in the Hepatopancreas of Swimming Crab Portunus trituberculatus: Cellular Stress Response and Tissue Damage

Ammonia is the most common contaminant in aquaculture systems. Due to the unexpected deterioration of natural seawater quality caused by harmful alga blooms in summer, the water exchange cycle for the culture ponds of the swimming crab Portunus trituberculatus, an important aquaculture species in China, is often much longer, and the crabs may be exposed to long-term ammonia stress. However, less information is available regarding the long-term effects of ammonia in marine decapod crustaceans. Therefore, it is of great significance to understand the toxic effects of prolonged ammonia in decapods. In this study, alteration of histology, cellular stress responses (CSRs), and apoptosis in the hepatopancreas of P. trituberculatus, an important aquaculture species, during ammonia stress (5, 15, and 45 mg⋅L–1) for 1, 7, and 15 days and recovery at the normal condition for 7 days, were analyzed. Our results demonstrated a serious impact of long-term (15 days) ammonia stress by depressing crab CSR especially when ammonia concentration exceeds 15 mg⋅L–1. Overall, short- (1 day) and medium-term (7 days) ammonia stress induced CSR, evidenced by upregulated expression of the genes involved in antioxidant defense (SOD, CAT, and GPX), apoptosis (p53, Bax, and Caspase-3), heat shock response (HSR) (Hsp70 and Hsp90), unfolded protein response (UPR) (IRE1, ATF6, and XBP1), and DNA damage response (DDR) (ATR and DNA-PKcs). However, long-term (15 days) ammonia stress, especially when exposed to the ammonia of 15 and 45 mg⋅L–1, resulted in a higher level of apoptosis and severe damage of hepatopancreas, which may be related to the depressed CSR including antioxidant defense, HSR, UPR, and DDR. Notably, after recovery, the expressions of many genes involved in apoptosis, antioxidant response, HSR, UPR, and DDR in the groups exposed to ammonia at 15 and 45 mg⋅L–1 were still significantly different to that of the control group. In summary, care should be taken when P. trituberculatus is exposed to ammonia over 15 mg⋅L–1 especially when exposure duration is longer than 15 days, as the CSR could be compromised. This study provides a reference for a comprehensive understanding of CSR in decapod crustaceans under ammonia stress and will be beneficial for management in the intensive culture of the swimming crab.

Chlorophyll and phycocyanin in-situ fluorescence in mixed cyanobacterial species assemblages: Effects of morphology, cell size and growth phase

Cyanobacteria harmful blooms can represent a major risk for public health due to potential release of toxins and other noxious compounds in the water. A continuous and high-resolution monitoring of the cyanobacteria population is required due to their rapid dynamics, which has been increasingly done using in-situ fluorescence of phycocyanin (f-PC) and chlorophyll a (f-Chl a). Appropriate in-situ fluorometers calibration is essential because f-PC and f-Chl a are affected by biotic and abiotic factors, including species composition. Measurement of f-PC and f-Chl a in mixed species assemblages during different growth phases - representative of most field conditions - has received little attention. We hypothesized that f-PC and f-Chl a of mixed assemblages of cyanobacteria may be accurately estimated if taxa composition and fluorescence characteristics are known. We also hypothesized that species with different morphologies would have different fluorescence per unit cell and biomass. We tested these hypotheses in a controlled culture experiment in which photosynthetic pigment fluorescence, chemical pigment extraction, optical density and microscopic enumeration of four common cyanobacteria species (Aphanocapsa sp, Microcystis aeruginosa, Dolichospermum circinale and Raphidiopsis raciborskii) were quantified. Both monocultures and mixed cultures were monitored from exponential to late stationary growth phases. The sum of fluorescence of individual species calculated for mixed samples was not significantly different than measured fluorescence of mixed cultures. Estimated and measured f-PC and f-Chl a of mixed cultures had higher correlations and smaller absolute median errors when estimations were based on fluorescence per biomass instead of fluorescence per cell. Largest errors were overestimations of measured fluorescence for species with different morphologies. Fluorescence per cell was significantly different among most species, while fluorescence per unit biomass was not, indicating that conversion of fluorescence to biomass reduces species-specific bias. This study presents new information on the effect of species composition on cyanobacteria fluorescence. Best practices of deployment and operation of fluorometers, and data-driven models supporting in-situ fluorometers calibration are discussed as suitable solutions to minimize taxa-specific bias in fluorescence estimates.

Transportation of bloom forming species in ballast water by commercial vessels at Yangshan deep water port

The introduction of bloom forming species through discharge of ships' ballast water is recognized as a global challenge to marine ecosystem. Harmful algal bloom species in ballast water is of special concern. This study examines the abundance and diversity of bloom forming species in ballast water from 44 samples collected in 2015–2016 from 40 commercial ships arriving at Yangshan deep water port, the world's largest intelligent container terminal. In total 21 bloom forming species were identified in these samples uptake from 10 different sea areas, belonging to Ochrophyta (13 species) and Myzozoa (8 species). Among these species, Dinophysis caudata, Prorocentrum lima, Prorocentrum cordatum and Prorocentrum micans could produce toxins. In the examined samples, the average abundance of organisms in size class ≥10–50 μm ranged from 183 ± 33 to 8055 ± 5648 cells L−1, among which the average abundance of bloom forming species ranged from 25 ± 35 to 2200 ± 2400 cells L−1. Although the average number of bloom forming species identified from the samples during the survey were in compliance with discharge standard according to the Regulation D-2 of the IMO BWM Convention, in some of the samples, these species accounted for 70%–97% of the total number of organisms in size class ≥10–50 μm. The results from this study also reveals that the abundance of bloom forming species is higher in water samples ballasted from coastal water than the ones from open sea. This study aims to collect data on harmful bloom forming species persisting in ballast water transported by commercial vessels arriving at Yangshan deep water port, with emphasis on identifying major species of the harmful marine micro-algae. It is quite essential to select a reliable detection method for detailed species analysis. It can provide biological mapping of harmful marine microalgae in the examined eco-system for better decision-making on biological invasion management.

From webs, loops, shunts, and pumps to microbial multitasking: Evolving concepts of marine microbial ecology, the mixoplankton paradigm, and implications for a future ocean

AbstractEmerging knowledge of mixoplankton—ubiquitous microbes that employ phototrophy and phagotrophy synergistically in one cell—reshapes our knowledge of the flow of materials and energy, with wide‐reaching impacts on marine productivity, biodiversity, and sustainability. Conceptual models of microbial interactions have evolved from food‐chains, where carbon‐fixing phytoplankton are conceived as being grazed solely by zooplankton that, in turn, support fisheries and higher trophic levels, to microbial webs, loops, and shunts, as knowledge about abundance, activity, and roles of marine microbial organisms—as well as the complexity of their interactions—has increased. In a future world, plankton that depend on a single strategy for acquiring nutrition (photo‐autotrophy or phago‐heterotrophy) may be disadvantaged with increasing temperatures and ocean acidification impacting vital rates, thermal stratification decreasing water column nutrient exchange, and anthropogenic pollution shifting amounts, forms, and proportions of nutrients. These conditions can lead to stoichiometric imbalances that may promote mixoplanktonic species with an increasing likelihood of harmful blooms. Such changes in plankton species composition alters the interconnectivity of oceanic microbes with direct consequences on biogeochemical cycling, trophic dynamics, and ecosystem services. Here, the implications of the mixoplankton paradigm relative to traditional concepts of microbial oceanography in a globally‐changing, anthropogenically‐impacted world are explored.