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Abstract Climate change elevates the threat of compound heat and drought events, with their ecological and socioeconomic impacts exacerbated by human ecosystem alterations such as eutrophication, salinization, and river engineering. Here, we study how multiple stressors produced an environmental disaster in a large European river, the Oder River, where a toxic bloom of the brackish-water planktonic haptophyte Prymnesium parvum (the “golden algae”) killed approximately 1000 metric tons of fish and most mussels and snails. We uncovered the complexity of this event using hydroclimatic data, remote sensing, cell counts, hydrochemical and toxin analyses, and genetics. After incubation in impounded upstream channels with drastically elevated concentrations of salts and nutrients, only a critical combination of chronic salt and nutrient pollution, acute high water temperatures, and low river discharge during a heatwave enabled the riverine mass proliferation of B-type P. parvum along a 500 km river section. The dramatic losses of large filter feeders and the spreading of vegetative cells and resting stages make the system more susceptible to new harmful algal blooms. Our findings show that global warming, water use intensification, and chronic ecosystem pollution could increase likelihood and severity of such compound ecoclimatic events, necessitating consideration in future impact models.

Climate change elevates the threat of compound heat and drought events, with their ecological and socioeconomic impacts exacerbated by human ecosystem alterations such as eutrophication, salinization, and river engineering. Here, we study how multiple stressors produced an environmental disaster in a large European river, the Oder River, where a toxic bloom of the brackish-water planktonic haptophyte Prymnesium parvum (the "golden algae") killed approximately 1000 metric tons of fish and most mussels and snails. We uncovered the complexity of this event using hydroclimatic data, remote sensing, cell counts, hydrochemical and toxin analyses, and genetics. After incubation in impounded upstream channels with drastically elevated concentrations of salts and nutrients, only a critical combination of chronic salt and nutrient pollution, acute high water temperatures, and low river discharge during a heatwave enabled the riverine mass proliferation of B-type P. parvum along a 500 km river section. The dramatic losses of large filter feeders and the spreading of vegetative cells and resting stages make the system more susceptible to new harmful algal blooms. Our findings show that global warming, water use intensification, and chronic ecosystem pollution could increase likelihood and severity of such compound ecoclimatic events, necessitating consideration in future impact models. [ABSTRACT FROM AUTHOR]

The golden alga Prymnesium parvum plays a key role in harmful algal blooms (HABs) worldwide, including the massive fish kills that occurred in the Oder river (Poland and Germany) in 2022. However, studies addressing this ecological disaster have to date focused mainly on the physicochemical parameters of the water, and overlooked the overall impact that environmental samples could have on aquatic organisms other than fish. Therefore, the present study evaluated the toxicological effect of the bloom by subjecting samples of the river water to microbiotests comprising organisms from two trophic levels: producers (Pseudokirchneriella subcapitata), and consumers (Daphnia magna and Thamnocephalus platyurus). In addition, the study examined the relative concentrations of prymnesins and the physicochemical parameters of the water samples, and 18S rRNA gene sequencing was used to examine eukaryotic assemblages in the samples. Among the tested organisms, D. magna was found to be most sensitive to the water samples from the disaster, with a maximum mortality of 90 % after 24 h. The 18S rRNA gene analysis found a high level of P. parvum in the tested samples during the ecological disaster (up to 9.2 %) compared to one month later (0.1 %). Our data indicates a notable increase in P. parvum and prymnesin level around the time of the ecological disaster in the Oder River in 2022, and that this may have played a part in its occurrence; in addition, D. magna may be an effective bioindicator for identifying the risk of P. parvum blooms to invertebrates. [ABSTRACT FROM AUTHOR]

Prymnesium parvum is a harmful alga found in brackish waters worldwide whose toxins can be lethal to aquatic organisms. Established field methods to control blooms of this species, however, are unavailable. Earlier studies showed that various extracts of giant reed (Arundo donax) can suppress P. parvum growth and that ellipticine, an allelochemical present in giant reed, is a potent algicide against this species. The unintended effects of giant reed products on nontarget organisms, however, are not fully understood. This study determined the effects of giant reed leachate (aqueous extract of dried chips) and ellipticine on growth of P. parvum and the green microalga Chlorella sorokiniana; survival and reproduction of the planktonic crustacean Daphnia pulex; and hatching success, larval survival, and larval swimming behavior of the teleost fish Danio rerio. Leachate made with 3 g chips L−1 was lethally toxic to P. parvum and D. pulex, stimulated C. sorokiniana growth, and impaired D. rerio behavior. Leachate at 1 g L−1 fully suppressed P. parvum growth, had moderate effects on D. pulex reproductive output, and had no effects on D. rerio. Ellipticine at 0.01 mg L−1 irreversibly inhibited P. parvum growth, acutely but reversibly inhibited C. sorokiniana growth, slightly delayed D. pulex reproduction, and had no effects on D. rerio. These observations suggest that when applied at appropriate concentrations, natural products derived from giant reed can be used as tools to specifically control P. parvum growth with minimal effects on nontarget species. [ABSTRACT FROM AUTHOR]

Cyanobacteria are the most common toxigenic algae in inland waters. Their toxins can affect the health of aquatic and terrestrial organisms, including humans. Other algal groups, such as haptophytes (e.g., Prymnesium parvum) and euglenoids (e.g., Euglena sanguinea), can also form harmful algal blooms (HABs) whose toxins cause injury to aquatic biota but currently have no known effects on human health. Prymnesium parvum, however, is responsible for some of the worst HAB-related ecological disasters recorded in inland waters. Here, we provide an overview of the primary toxigenic algae found in U.S. inland waters: cyanobacteria (planktonic forms), P. parvum, and E. sanguinea with the objective of describing their similarities and differences in the areas of HAB ecology, algal toxins, and the potential for future range expansion of HABs. A detailed account of bloom habitats and their known associations with land cover and use is provided from the perspective of water quality. This review revealed that salinity may have an influence on inland cyanobacterial blooms and cyanotoxins that had not been fully recognized previously. [ABSTRACT FROM AUTHOR]

• C-type prymnesins were identified in the Prymnesium parvum isolated from China. • Growth of P. parvum was inhibited by nitrate limitation but not by low salinity. • The quotas of prymnesins per cell increased in P. parvum under nitrogen limitation. • The quotas of prymnesins per cell increased in P. parvum under low salinity (14). • Toxin quotas per cell also increased with the extension of culture period. Fish-killing events caused by haptophyte Prymnesium parvum have been reported in aquatic environments worldwide. This haptophyte could produce diverse prymnesins (PRMs) that harm to aquatic organisms like fishes. In this study, the components of prymnesins in the strain of P. parvum (NMBjih029) isolated from the coast of Ningbo city, China, were elucidated by a high-resolution mass spectrometer (HRMS), and the influence of nitrate levels and salinity on growth and toxin production of P. parvum were also explored. Results showed that the P. parvum produced C-type prymnesins with structure variations in saturation, chlorination, and sugar modifications. The growth and toxin production were significantly affected by nitrate levels in the batch cultures. At the lowest level of nitrate (N:P = 4:1), growth of P. parvum was inhibited but toxin quotas per cell increased up to approximately 4 times of that in control group (N:P = 16:1) during the exponential growth stage. Growth of P. parvum was not obviously affected by different salinities, but the biosynthesis of prymnesins increased with decreasing salinity from 32 to 14 in the culture media. The proportion of high chlorination of prymnesins (tetrachloride) increased in P. parvum under nitrogen limitation stress and low salinity. And the toxin quotas per cell also markedly increased with the extension of culture period in P. parvum under nitrogen limitation and different salinity conditions. This study provides some important cues for toxin profile and environmental impacts on the biosynthesis of prymnesins in the strain of P. parvum isolated from Chinese aquatic environments. [ABSTRACT FROM AUTHOR]

• Hemolytic potency of prymnesin groups reflects their cytotoxic potential. • Presence of sterols can impact the hemolytic potency of prymnesins. • Prymnesin profile influences toxicity. • A- and B-type prymnesins probably exhibit different membrane interactions. Prymnesins, produced by the haptophyte Prymnesium parvum , are considered responsible for fish kills when this species blooms. Although their toxic mechanism is not fully understood, membrane disruptive properties have been ascribed to A-type prymnesins. Currently it is suggested that pore-formation is the underlying cause of cell disruption. Here the hypothesis that A-, B-, and C-type prymnesins interact with sterols in order to create pores was tested. Prymnesin mixtures containing various analogs of the same type were applied in hemolysis and cytotoxicity assays using Atlantic salmon Salmo salar erythrocytes or rainbow trout RTgill-W1 cells. The hemolytic potency of the prymnesin types reflected their cytotoxic potential, with approximate concentrations reaching 50 % hemolysis (HC 50) of 4 nM (A-type), 54 nM (C-type), and 600 nM (B-type). Variabilities in prymnesin profiles were shown to influence potency. Prymnesin-A (3 Cl) + 2 pentose + hexose was likely responsible for the strong toxicity of A-type samples. Co-incubation with cholesterol and epi-cholesterol pre-hemolysis reduced the potential by about 50 % irrespective of sterol concentration, suggesting interactions with sterols. However, this effect was not observed in RTgill-W1 toxicity. Treatment of RTgill-W1 cells with 10 µM lovastatin or 10 µM methyl-β-cyclodextrin-cholesterol modified cholesterol levels by 20-30 %. Regardless, prymnesin cytotoxicity remained unaltered in the modified cells. SPR data showed that B-type prymnesins likely bound with a single exponential decay while A-types seemed to have a more complex binding. Overall, interaction with cholesterol appeared to play only a partial role in the cytotoxic mechanism of pore-formation. It is suggested that prymnesins initially interact with cholesterol and stabilize pores through a subsequent, still unknown mechanism possibly including other membrane lipids or proteins. [Display omitted] [ABSTRACT FROM AUTHOR]

Prymnesium parvum is a toxic algal bloom (HAB)-forming species. The toxicity of this alga is a result of a collection of compounds known as prymnesins. Prymnesins exert harmful effects upon fish, shellfish, and mollusks, causing huge economic losses. In the present study, a new method was developed for the detection of P. parvum. The novel method utilizes isothermal amplification, known as recombinase polymerase amplification (RPA), in combination with lateral-flow dipstick (LFD). Herein, a set of primers and probes were designed for internal transcribed spacer (ITS) sequences, and a specific and sensitive RPA-LFD rapid detection method was established for P. parvum. Meanwhile, we verified its feasibility for the detection of environmental samples. It was demonstrated that the optimal amplification temperature and time for RPA were 39°C and 15 min. RPA/RPA-LFD was experimentally verified to be specific, demonstrating no cross-reaction with distinct control microalgae, and furthermore, the total time required for the RPA-LFD experiment was 20 min. Meanwhile, the detection limit for the genomic DNA of P. parvum was 1.5×10-1 pg/μL, and the detection limit for plasmids was 2.35 pg/μL. In addition, the results herein revealed that the RPA-LFD assay was 100 times more sensitive than PCR for detection of P. parvum. In conclusion, we developed an RPA-LFD that does not require precision instruments, and can be utilized for rapid on-site detection of P. parvum. In the future, the RPA-LFD can be considered for practical application for environmental detection of the toxic algal species.

Harmful algal blooms (HABs), caused by the rapid proliferation or aggregation of microorganisms, are catastrophic for the environment. The Prymnesium parvum is a haptophyte algal species that is found worldwide and is responsible for extensive blooms and death of larval amphibians and bivalves, causing serious negative impacts on the ecological environment. For the prevention and management of environmental pollution, it is crucial to explore and develop early detection strategies for HABs on-site using simple methods. The major challenge related to early detection is the accurate and sensitive detection of algae present in low abundance. Herein, recombinase polymerase amplification (RPA) was combined with clustered regularly interspaced short palindromic repeats and Cas12a protein (CRISPR - LbaCas12a) systems, and the lateral flow dipstick (LFD) was used for the first time for early detection of P. parvum. The internal transcribed spacer (ITS) of P. parvum was selected as the target sequence, and the concentration of single - strand DNA reporters, buffer liquid system, reaction time, and amount of gold particles were optimized. The RPA-CRISPR - LbaCas12a - LFD approach demonstrated highly specificity during experimental testing, with no cross - reaction against different microalgae used as controls. In addition, the lowest detection limit was 10,000 times better than the lowest detection limit of the standalone RPA approach. The feasibility and robustness of this approach were further verified by using the different environmental samples. It also observed that P. parvum are widely distributed in Chinese Sea, but the cell density of P. parvum is relatively low (<0.1 cells/mL). The developed approach has an excellent specificity and offers 10,000 times better sensitivity than the standalone RPA approach. These advantages make this approach suitable for early warning detection and prevention of HAB events in environmental water. Also, the outcomes of this study could promote a shift from traditional laboratory-based detection to on-site monitoring, facilitating early warning against HABs. [Display omitted] • First application to use RPA with CRISPR - LbaCas12a systems and LFD for the detection of Prymnesium parvum. • In this study, the additions of CRISPR made the method more specific and 10,000 times more sensitive than standalone RPA. • The detection period was short, and the RPA - CRISPR - LbaCas12a - LFD reaction could be completed in two steps. • The feasibility and robustness of RPA - CRISPR - LbaCas12a - LFD assay for detection of P. parvum was verified by using environmental water samples. [ABSTRACT FROM AUTHOR]

The purpose of this study was to evaluate the optimum environmental condition required for reaching the maximum growth rate of P. parvum. Eight ions (Na+, K+, CO32−, HCO3−, Ca2+, Mg2+, Cl−, and SO42−) were divided into two groups with a uniform design of 4 factors and 10 levels. The results showed a rising trend in growth rate with increasing ion concentrations. However, concentrations that exceeded the threshold led to a slowdown in the growth rate. Therefore, adequate supply of ion concentrations promoted growth of P. parvum, whereas excessively abundant or deficient ion concentrations inhibited its growth rate. Specifically, the order of impact of the first four ion factors on the growth rate was Na+ > HCO3− > K+ > CO32−. The growth rate of P. parvum reached the maximum theoretical 0.999 when the concentrations of Na+, K+, CO32−, and HCO3− ions were 397.98, 11.60, 3.37, and 33.31 mg/L, respectively. This theoretical growth maximum was inferred from the experimental results obtained in this study. For other ion factors, SO42− had the most influence on the growth rate of P. parvum, followed by Mg2+, Ca2+, and Cl− ions. The growth rate of P. parvum reached the maximum theoretical value of 0.945 when the concentrations of Ca2+, Mg2+, Cl−, and SO42− ions were 11.52, 32.95, 326.29, and 377.31 mg/L, respectively. The findings presented in this study add to our understanding of the growth conditions of P. parvum and provide a theoretical basis for dealing with the water bloom it produces in order to control and utilize it. [ABSTRACT FROM AUTHOR]

Prymnesium parvum is an environmentally harmful algae and well known for its toxic effects to the fish culture. However, there is a dearth of studies on the growth behavior of P. parvum and information on how the availability of nutrients and environmental factors affect their growth rate. To address this knowledge gap, we used a uniform design approach to quantify the effects of major nutrients (N, P, Si and Fe) and environmental factors (water temperature, pH and salinity) on the biomass density of P. parvum. We also generated the growth model for P. parvum as affected by each of these nutrients and environmental factors to estimate optimum conditions of growth. Results showed that P. parvum can reach its maximum growth rate of 0.789, when the water temperature, pH and salinity is 18.11 °C, 8.39, and 1.23‰, respectively. Moreover, maximum growth rate (0.895–0.896) of P. parvum reached when the concentration of nitrogen, phosphorous, silicon and iron reach 3.41, 1.05, 0.69 and 0.53 mg/l, respectively. The order of the effects of the environmental factors impacting the biomass density of P. parvum was pH > salinity > water temperature, while the order of the effects of nutrients impacting the biomass density of P. parvum was nitrogen > phosphorous > iron > silicon. These findings may assist to implement control measures of the population of P. parvum where this harmful alga threatens aquaculture industry in the waterbodies such as Ningxia region in China. [ABSTRACT FROM AUTHOR]

The Jim Bertram Lake System consists of several stream impoundments within the City of Lubbock, Texas (USA). Baseflow in the upstream reach is dominated by nitrogen-rich-treated wastewater. While toxic blooms of Prymnesium parvum have occurred in this system for ∼2 decades during fall or winter-spring, little is known about water quality variables that facilitate blooms or the alga's spatiotemporal distribution. Water quality associations were examined monthly over a 1-year period. Total phosphorus was largely below the detection limit, suggesting that the system is phosphorus limited. Algal abundance was low during the assessment period and associations were determined using multiple logistic regression. Algal incidence was negatively associated with temperature and positively with organic nitrogen and calcium hardness. These findings conform with earlier reports but positive associations with the latter two variables are noteworthy because they have not been widely confirmed. Spatiotemporal distribution was evaluated in fall and winter-spring of three consecutive years. Prymnesium parvum incidence was higher in the upper than in the lower reach, and detections in the lower reach occurred only after a dense bloom developed in the upper reach contemporaneously with stormwater runoff-associated flooding. Thus, the upstream reach is a major source of propagules for downstream sites. Because urban runoff is a source of phosphorus and its nitrogen: phosphorus ratio is lower than prevailing ratios in the upper reach, what triggered the bloom was likely relief from phosphorus limitation. This study provided water quality, geographic and hydrological indices that may inform prevention and control methods for harmful algae in nitrogen-enriched urban systems. [ABSTRACT FROM AUTHOR]

Harmful algal blooms are a significant environmental problem. Cells that bloom are often associated with intercellular or dissolved toxins that are a grave concern to humans. However, cells may also excrete compounds that are beneficial to their competition, allowing the cells to establish or maintain cells in bloom conditions. Here, we develop a yeast cell assay to assess whether the bloom-forming species can change the toxicity of the water environment. The current methods of assessing toxicity involve whole organisms. Here, yeast cells are used as a bioassay model to evaluate eukaryotic cell toxicity. Yeast is a commonly used, easy to maintain bioassay species that is free from ethical concerns, yet is sensitive to a wide array of metabolic and membrane-modulating agents. Compared to methods in which the whole organism is used, this method offers rapid and convenient cytotoxicity measurements using a lower volume of samples. The flow cytometer was employed in this toxicology assessment to measure the number of dead cells using alive/dead stain analysis. The results show that yeast cells were metabolically damaged after 1 h of exposure to our model toxin-producing euryhaline flagellates (Heterosigma akashiwo and Prymnesium parvum) cells or extracts. This amount was increased by extending the incubation time.

To better comprehend microbial invasions, researchers need more insight into how environmental conditions affect biogeographic patterns in microbes. Recent study suggests that environmental conditions are important predictors for when invasive microbes might become established, actively participating members of a community, but that dispersal also can be important in determining invasion success in conducive environments. In this study, we explored how detection limits affected the ability of a local-scale environmental model to predict the presence of the putative microbial invader Prymnesium parvum at a regional scale. The local-scale model was robust when applied to the regional dataset. Regardless of sensitivity (i.e., minimum detection limit used), P. parvum presence was well predicted by environmental parameters. The highest accuracy was obtained at a detection limit that corresponds with detection limits routinely achieved using standard microscope-based analysis, while lower detection limits typical of molecular approaches worsened the model's predictive capabilities. Although many mechanisms may be limiting our ability to predict P. parvum presence at low abundances (e.g., dispersal, source-sink dynamics, methodological limitations), we argue here that environmental filtering plays a role in regulating population growth above these low abundances. The importance of environmental traits in predicting the presence of this microbial species suggests that environmental conditions are critical determinants of the establishment and spread of P. parvum. [ABSTRACT FROM AUTHOR]

Abstract The Prymnesium parvum is a common nearshore harmful alga that secretes hemolytic ichthyotoxin, which affects gills of shellfish and induce death, thereby resulting in severe economic losses of aquaculture. In this study, the loop-mediated isothermal amplification (LAMP) was employed in combination with the lateral flow dipstick (LFD) visual detection method to establish a rapid LAMP-LFD detection method for P. parvum. Approximately 50 min of LAMP amplification was necessary to generate the LFD results, which was about 2.5 h shorter than that of conventional PCR. Moreover, the LAMP-LFD method had excellent specificity, as indicated by the negative results for other common harmful algal species. It could detect genomic DNA at the lowest concentration of 3 × 10−2 ng μL−1. Therefore, the LAMP-LFD method could specifically and effectively detect target ITS sequence (including the 5.8S rDNA) of P. parvum , which is relatively simple and does not require specialized instruments. Consequently, it could be used as a rapid field detection method for the detection of low-density P. parvum as well as for the prevention of microalgal blooms. Highlights • The first report of LAMP-LFD assay established in harmful algae of P. parvum. • The LAMP-LFD method accurately identified algal isolates of P. parvum but did not detect other algal isolates, which showed a high specificity. • The LAMP-LFD method is more ideal for low-equipment setting research institution and for on-site detecting. [ABSTRACT FROM AUTHOR]

Anthropogenic activity is leading to increasing frequency and magnitude of disturbance in freshwater systems throughout the world. In turn, disturbance events are more likely to co-occur, compounding effects. Here we present a case study in which we investigated how the effects of co-occurring disturbances might interact to influence the abundance of a harmful algal bloom-forming species, Prymnesium parvum. The disturbances applied here included increased salinity, community composition change via the removal of large zooplankton, and elevated propagule pressure of P. parvum. We also examined the role that historical exposure to one of the disturbances played in influencing the effect of the co-occurring disturbances. We show that these types of disturbances can lead to synergistic or compounded effects, here influencing the abundance of a harmful algal species, and that historical exposure to a disturbance can influence this effect. These findings highlight the important role of increased and co-occurring disturbance in aquatic ecosystems and the role it may play in the formation of harmful algae blooms as the frequency of these occurrences increases. [ABSTRACT FROM AUTHOR]

Mixotrophy is a combination of photosynthesis and direct access to organic carbon sources, mainly through osmotrophy or phagotrophy. This strategy is adopted by several, phylogenetically distinct, phytoplankton groups and is commonly occurring in marine, brackish and freshwater ecosystems. Traditionally, it has been put in relation to both scarcity of inorganic nutrients and poor light conditions. However, we observed blooms of the mixotrophic, toxic haptophyte Prymnesium parvum in different periods of the year and under variable resources availability. The analysis of a 6.5-year data set of phytoplankton weekly records from a Sicilian shallow lake (Biviere di Gela, south-eastern Sicily) allowed us to hypothesise that a depleted condition as regards inorganic nutrients is not the main fuel to the growth of P. parvum, neither this is due to light limitation. The results achieved show that an increased availability in suitable preys can stimulate the growth of this phagotrophic photoautotroph. Contemporarily, it was not found any clear environmental patterns to explain species dominance and growth patterns as related to inorganic nutrient availability. Moreover, it is shown that these organisms tend to monopolise resources when these become available irrespective of seasons, and under variable conditions as regards inorganic nutrient availability. [ABSTRACT FROM AUTHOR]

• Using ecological niche models and niche analyses to predict distribution of Prymnesium parvum. • Populations in the USA, Europe and Australia occupies non-overlapping climatic conditions. • MaxEnt models accurately uncovered novel suitable areas, not yet occupied by P. parvum. • Lower minimum temperatures in the coldest month are associated with higher occurrence probabilities of the species, in agreement with ecophysiology of blooms. • Increasing precipitation reduced occurrence probabilities, suggesting spread under on-going salinization of freshwaters. Freshwater ecosystems are highly susceptible to harmful algal blooms (HABs), which are often caused by monospecific dense blooms. Effective preventive management strategies are urgently needed to avoid wide-ranging and severe impacts often resulting in costly damage to resources and unsustainable management options. In this study, we utilized SDM techniques focused on Prymnesium parvum , one of the most notorious HABs species worldwide. We first compare the climatic space occupied by P. parvum in North America, Europe and Australia. Additionally, we use MaxEnt algorithm to infer, for the first time, the potentially suitable freshwater environments in the aforementioned ranges. We also discuss the risks of invasion in reservoirs – prone habitats to persistent blooms of pests and invasive phytoplanktonic species. Our results show populations with distinctive niches suggesting ecophysiological tolerances, perhaps reflecting different strains. Our model projections revealed that the potential extent for P. parvum invasions is much broader than its current geographic distribution. The spatial configuration of reservoirs, if not sustaining dense blooms due to non-optimal conditions, favors colonization of multiple basins and ecoregions not yet occupied by P. parvum. Our models can provide valuable insights to decision-makers and monitoring programs while reducing the resources required to control the spread of P. parvum in disturbed habitats. Lastly, as impact magnitude is influenced by toxicity which in turn varies between different strains, we suggest future studies to incorporate intraspecific genetic information and fine-scale environmental variables to estimate potential distribution of P. parvum. [ABSTRACT FROM AUTHOR]

Environmental DNA (eDNA) metabarcoding is a relatively new monitoring tool featuring in an increasing number of applications such as the facilitation of the accurate and cost effective detection of species in environmental samples. eDNA monitoring is likely to have a major impact on the ability of salmonid aquaculture industry producers and their regulators to detect the presence and abundance of pathogens and other biological threats in the surrounding environment. However, for eDNA metabarcoding to develop into a useful bio-monitoring tool it is necessary to (a) validate that sequence datasets derived from amplification of metabarcoding markers reflect the true species’ identity, (b) test the sensitivity under different abundance levels and environmental noise and (c) establish a low-cost sequencing method to enable the bulk processing of field samples. In this study, we employed an elaborate experimental design whereby different combinations of five biological agents were crossed at three abundance levels and exposed to sterile pre-filtered and unfiltered seawater, prior to coarse filtering and then eDNA ultrafiltration of the resultant material. We then benchmarked the low-cost, scalable, Ion Torrent sequencing method against the current gold-standard Illumina platform for eDNA surveys in aquaculture. Based on amplicon-seq of the 18S SSU rDNA v9 region, we were able to identify two parasites (Lepeophtheirus salmonis and Paramoeba perurans) to species level, whereas the microalgae species Prymnesium parvum, Pseudo-nitzschia seriata, and P. delicatissima could be assigned correctly only to the genus level. Illumina and Ion Torrent provided near identical results in terms of community composition in our samples, whereas Ion Torrent was more sensitive in detecting species richness when the medium was unfiltered seawater. Both methods were able to reflect the difference in relative abundance between treatments in 4 out of 5 species when samples were exposed to the unfiltered seawater, despite the significant amount of background noise from both bacteria and eukaryotes. Our findings indicate that eDNA metabarcoding offers significant potential in the monitoring of species harmful to aquaculture and for this purpose, the low-cost Ion Torrent sequencing is as accurate as Illumina in determining differences in their relative abundance between samples.

This study introduces a comprehensive method for quantifying mass mortality events in freshwater wildlife, exemplified by the ecological disaster in the Odra River in 2022. Our approach integrates field observations, statistical analysis, and ecological assessment to measure the impact of such events on various aquatic species. Key steps include systematic counting of deceased organisms, assessing population declines, and evaluating the ecological repercussions of invasive species. Utilizing the R programming language, we developed a framework that is adaptable to similar ecological crises in different aquatic environments. This methodology facilitates a detailed understanding of the scale and implications of mass mortality events, thereby contributing to effective environmental management and conservation efforts. •The analysis and modeling methods of the disaster are presented in the R programming language.•Exclusively open-source software was used for the analysis.•The analysis includes detailed data on the disaster's impact on various species., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported., (© 2024 The Authors. Published by Elsevier B.V.)

Clay minerals have previously been used to mitigate algal blooms because of their ability to flocculate algal cells or remove nutrients, but also offer considerable potential to remove ichthyotoxins. When a barramundi farm in tropical Australia suffered substantial fish mortalities due to a bloom of the ichthyotoxic haptophyte Prymnesium parvum, the farm manager decided to manipulate pond water N:P ratios through removal of phosphorus by the addition of lanthanum-modified bentonite clay (Phoslock™) to successfully mitigate ichthyotoxic effects. We conducted Prymnesium culture experiments under a range of N:P ratios, screening 14 different clays (two zeolites, four kaolins, six bentonites and two types of Korean loess) at pH 7 and 9 for cell flocculation and removal of ichthyotoxicity assessed with the RTgill-W1 cell line assay. Application of Phoslock™ to cultures grown at different N:P effectively removed 60%–100% of water-soluble toxicity of live Prymnesium (dependent on nutritional status). While most clays efficiently flocculated Prymnesium cells (≥80% removal), cell removal proved a poor predictor of ichthyotoxin adsorption. Extensive clay screening revealed that at elevated pH, as commonly associated with dense algal blooms, most clays either exacerbated ichthyotoxicity or exhibited significantly reduced toxin adsorption. Interpretation of changes in clay zeta potential at pH 7 and 9 provided valuable insight into clay/ichthyotoxin interactions, yet further research is required to completely understand the adsorption mechanisms. Bentonite-type clays proved best suited for ichthyotoxin removal purposes (100% removal at ecologically relevant pH 9) and offer great potential for on-farm emergency response.

Graphical abstract Highlights • Prymnesium parvum produces three prymnesin types (A–C). • Individual isolates produce only one type, but several analogues. • Prymnesin types showed complex biogeographical distributions. • ITS-sequences revealed monophyletic origin of prymnesins. • Perfect match between chemotype and phylotype as defined by ITS. Abstract Harmful blooms formed by planktonic microalgae (HABs) in both freshwater and coastal waters regularly lead to severe mortalities of fish and invertebrates causing substantial economic losses of marine products worldwide. The mixotrophic haptophyte Prymnesium parvum is one of the most important microalgae associated with fish kills. Here 26 strains of P. parvum with a wide geographical distribution were screened for the production of prymnesins, the suspected causative allelochemical toxins. All investigated strains produced prymnesins, indicating that the toxins play an important role for the organism. The prymnesins can be classified into three types based on the length of the carbon backbone of the compound and each algal strain produced only one of these types. Biogeographical mapping of the prymnesin distribution indicated a global distribution of each type. In addition, phylogenetic analyses based on internal transcribed spacer (ITS) sequences revealed monophyletic origin of all prymnesin types and clades could therefore be defined based on the toxic compound. It might be that evolution of new species within the P. parvum species complex is driven by changes in toxin type or that they are a result of it. Such a correlation between chemotype and phylotype has never been documented before for a harmful microalga. Chemotaxonomy and ITS-type classification may thus be used to further delimit the P. parvum species complex. [ABSTRACT FROM AUTHOR]

Typical harmful micro-algal species constantly occurred in high density in marine aquaculture ponds in Xiangshan and Sanmen Bay, Zhejiang Province. Fates of the microalgal cells influenced by activity of the cultured animals largely determined the effects of the harmful microalgae. However, it is difficult to detect the in situ process. In this paper, toxic activities of three harmful microalga, namely Prymnesium parvum, Pleurochrysis elongata, Karlodinium veneficum, which were isolated from the local ponds, were comparatively studied based on brine shrimp toxic bioassays. Different lethal activities of live cells, cell debris, cellular extracts, and cell free mediums prepared by different process were analyzed. The results showed that, (1) all of the three microalgal species had density and time dependent lethal effects on Artermia nauplii, while P. parvum was the most toxic one and had acute lethal effects in 5 h. No such acute lethal effects were observed in P. elongata or K. veneficum; (2) live cells, cell debris and cellular extracts of P. parvum had the same lethal pattern. Prymnesins, toxin from P. parvum, is probably not exotoxic active; For P. elongata, toxic activity mainly came from live cells and cell debris; For K. veneficum, toxic activity was relatively lower compared with the other two species. However, Karlotoxin, toxin from K. veneficum, is exotoxic active. Physical disturbance triggered K. veneficum cells actively releasing toxins, which made it an active predator. [ABSTRACT FROM AUTHOR]

A suite of glycosylated glycerol derivatives representing various fragments of the glycosylated ichthyotoxins called prymnesins were chemically synthesised. Glycerol was used to represent a small fragment of the prymnesin backbone, and was glycosylated at the 2° position with the sugars currently reported to be present on prymnesin toxins. Neighbouring group participation was utilised to synthesise 1,2- trans -glycosides. SnCl 2 -promoted glycosylation with furanosyl fluorides gave 1,2- cis -furanosides with moderate stereocontrol, whilst TMSOTf promoted glycosylation with a furanosyl imidate gave a 1,2- cis -furanoside with good stereocontrol. The chemical synthesis of two larger glyceryl diglycoside fragments of prymnesin-1, glycosylated with α-ʟ-arabinopyranose and α-ᴅ-ribofuranose, is also described. As the stereochemistry of the prymnesin backbones at this region is undefined, both the 2 R - and 2 S- glycerol isomers were synthesised. The separated diastereoisomers were distinguished by comparing NOESY NMR with computational models. [ABSTRACT FROM AUTHOR]

The toxigenic haptophyte Prymnesium parvum is a mixotrophic phytoplankter with an extensive historic record of forming nearly monospecific, high-biomass, ecosystem-disrupting blooms, and it has been responsible for major fish kills in brackish waters and aquaculture facilities in many regions of the world. Little is known about how this species responds to commonly occurring environmental contaminants, or how nutrient (nitrogen, phosphorus) pollution may interact with environmentally relevant pesticide exposures to affect this harmful algal species. Here, standard algal toxicity bioassays from pesticide hazard assessments were used along with modified erythrocyte lysis assays to evaluate how atrazine exposures, imbalanced nutrient supplies, and salinity interact to influence the growth and toxicity in P. parvum isolates from three different regions. In nutrient-replete media, P. parvum 96 h IC 50 s ranged from 73.0 to 88.3 μg atrazine L −1 at salinity 10 and from 118 to >200 μg atrazine μg L −1 at salinity 20, and the response depended on the strain and the test duration. Relative hemolytic activity, used as an indication of toxicity, was a function of herbicide exposure, nutrient availability, salinity, geographic origin, and interactions among these factors. Highest levels of hemolytic activity were measured from a South Carolina strain in low-nitrogen media with high atrazine concentrations. Herbicide concentration was related to relative hemolytic activity, although a consistent relationship between growth phase and toxicity was not observed. Overall, these findings suggest that increasing chemical contamination is helping to promote ecosystem-disruptive, strongly mixotrophic algal blooms. [ABSTRACT FROM AUTHOR]

Microbial communities are comprised of complex assemblages of highly interactive taxa. We employed network analyses to identify and describe microbial interactions and co-occurrence patterns between microbial eukaryotes and bacteria at two locations within a low salinity (0.5-3.5 ppt) lake over an annual cycle. We previously documented that the microbial diversity and community composition within Lake Texoma, southwest USA, were significantly affected by both seasonal forces and a site-specific bloom of the harmful alga, Prymnesium parvum. We used network analyses to answer ecological questions involving both the bacterial and microbial eukaryotic datasets and to infer ecological relationships within the microbial communities. Patterns of connectivity at both locations reflected the seasonality of the lake including a large rain disturbance in May, while a comparison of the communities between locations revealed a localized response to the algal bloom. A network built from shared nodes (microbial operational taxonomic units and environmental variables) and correlations identified conserved associations at both locations within the lake. Using network analyses, we were able to detect disturbance events, characterize the ecological extent of a harmful algal bloom, and infer ecological relationships not apparent from diversity statistics alone. [ABSTRACT FROM AUTHOR]

Continued anthropogenic carbon emissions are expected to cause a decline in global average pH of the oceans to a projected value of 7.8 by the end of the century. Understanding how harmful algal bloom (HAB) species will respond to lowered pH levels will be important when predicting future HAB events and their ecological consequences. In this study, we examined how manipulated pH levels affected the growth rate of three strains of Prymnesium parvum from North America, Denmark and Japan. Triplicate strains were grown under pH conditions ranging from 6.6 to 9.1 to simulate plausible future levels. Different tolerances were evident for all strains. Significantly higher growth rates were observed at pH 6.6–8.1 compared to growth rates at pH 8.6–9.1 and a lower pH limit was not observed. The Japanese strain (NIES-1017) had the highest maximum growth rate of 0.39 divisions day −1  at pH 6.6 but a low tolerance (0.22 divisions day −1 ) to high levels (pH 9.1) with growth declining markedly after pH 7.6. The Danish (SCCAP K-0081) and North American (UTEX LB 2797) strains had maximum growth rates of 0.26 and 0.35 divisions day −1 , respectively between pH 6.6–8.1. Compared to the other two strains the Danish strain had a statistically lower growth rate across all pH treatments. Strain differences were either attributed to their provenance or the length of time the strain had been in culture. [ABSTRACT FROM AUTHOR]

Prymnesium parvum is a toxin-producing microalga that causes harmful algal blooms globally, which often result in large-scale fish kills that have severe ecological and economic implications. Although many toxins have previously been isolated from P. parvum, ambiguity still surrounds the responsible ichthyotoxins in P. parvum blooms and the biotic and abiotic factors that promote bloom toxicity. A major fish kill attributed to P. parvum occurred in Spring 2015 on the Norfolk Broads, a low-lying set of channels and lakes (Broads) found on the East of England. Here, we discuss how water samples taken during this bloom have led to diverse scientific advances ranging from toxin analysis to discovery of a new lytic virus of P. parvum, P. parvum DNA virus (PpDNAV-BW1). Taking recent literature into account, we propose key roles for sialic acids in this type of viral infection. Finally, we discuss recent practical detection and management strategies for controlling these devastating blooms. [ABSTRACT FROM AUTHOR]

• Use of flow cytometry to quantify ingestion rate of the toxic mixoplankton Prymnesium parvum. • Addition of algal prey significantly increased the growth rate of P. parvum both in inorganic phosphorus deficiency and sufficiency cultures. • Rates of ingestion and the lytic effects were stimulated by inorganic phosphorus deficiency in P. parvum. • P. parvum is able to use prey and/or debris derived from algae as phosphorus sources. Many harmful algae are mixoplanktonic, i.e. they combine phototrophy and phagotrophy, and this ability may explain their ecological success, especially when environmental conditions are not optimal for autotrophic growth. In this study, laboratory experiments were conducted with the mixotrophic and ichthyotoxic haptophyte Prymnesium parvum (strain CCAP 946/6) to test the effects of phosphorus (P) sufficiency and deficiency on its growth rate, phagotrophic and lytic activities. P-deficient P. parvum cultures were grown without or with addition of P in the form of inorganic phosphorus (nutrients) and/or living algal prey (i.e. the cryptophyte Teleaulax amphioxeia). The ingestion rate of P. parvum and prey mortality rate were calculated using flow cytometry measurements based on pigment-derived-fluorescence to distinguish between prey, predators and digesting predators. The first aim of the study was to develop a method taking into account the rate of digestion, allowing the calculation of ingestion rates over a two-week period. Growth rates of P. parvum were higher in the treatments with live prey, irrespective of the concentration of inorganic P, and maximum growth rates were found when both inorganic and organic P in form of prey were added (0.79 ± 0.07 d -1). In addition, the mortality rate of T. amphioxeia induced by lytic compounds was 0.2 ± 0.02 d -1 in the P-deficient treatment, while no mortality was observed under P-sufficiency in the present experiments. This study also revealed the mortality due to cell lysis exceeded that of prey ingestion. Therefore, additional experiments were conducted with lysed prey cells. When grown with debris from prey cells, the mean growth rate of P. parvum was similar to monocultures without additions of prey debris (0.30 ± 0.1 vs. 0.38 ± 0.03 d -1), suggesting that P. parvum is able to grow on prey debris, but not as fast as with live prey. These results provide the first quantitative evidence over two weeks of experiment that ingestion of organic P in the form of living prey and/or debris of prey plays an important role in P. parvum growth and may explain its ecological success in a nutrient-limited environments. [Display omitted] [ABSTRACT FROM AUTHOR]

The dinoflagellate Alexandrium minutum and the haptophyte Prymnesium parvum are well known for their toxin production and negative effects in marine coastal environments. A. minutum produces toxins which cause paralytic shellfish poisoning in humans and can affect copepods, shellfish and other marine organisms. Toxins of P. parvum are associated with massive fish mortalities resulting in negative impacts on the marine ecosystem and large economic losses in commercial aquaculture. The aim of this work is to improve our knowledge about the reliability of the use of marine invertebrate bioassays to detect microalgae toxicity, by performing: (i) a 24- to 48-h test with the brine shrimp Artemia franciscana; (ii) a 48-hour embryo-larval toxicity test with the sea urchin Paracentrotus lividus; and (iii) a 72-h test with the amphipod Corophium multisetosum. The results indicate that A. franciscana and P. lividus larvae are sensitive to the toxicity of A. minutum and P. parvum. LC50 comparison analysis between the tested organisms reveals that A. franciscana is the most sensitive organism for A. minutum. These findings suggest that the use of different organizational biological level bioassays appears to be a suitable tool for A. minutum and P. parvum toxicity assessment.

During the last century, the blooms of the toxic haptophyte Prymnesium parvum have been responsible for massive fish kills in both aquaculture and wild populations. Despite decades of research, the ichthyotoxic properties of P. parvum, and how this alga affects fish, is still debated. Using a novel device to measure the respirometry, ventilation volume, ventilation frequency, oxygen extraction, and oxygen consumption of undisturbed European plaice (Pleuronectes platessa) were acquired during exposure to two algal species as well as hypoxia. Fourteen fish (258 ± 44 g) were initially exposed to severe hypoxia and left to recover for at least 48 h. Half of these fish were then exposed to known harmful concentrations of P. parvum (median ± standard deviation (SD); 2.6 × 105 ± 0.6 × 105 cells mL−1), while the remaining half were exposed to the non-toxic alga Rhodomonas salina (median ± SD; 3.2 × 105 ± 0.7 × 105 cells mL−1). During exposure to severe hypoxia, all of the fish were able to maintain oxygen consumption by increasing the ventilation volume. The results from fish that were exposed to P. parvum showed a significant decrease in oxygen extraction (median ± SD; 52.6 ± 6.9 percentage points) from pre-exposure to the end of the experiment, as opposed to fish exposed to R. salina, which were unaffected. These results indicate that suffocation affects the European plaice when exposed to P. parvum. The observed severe decrease in oxygen extraction can be ascribed to either damage of the gill epithelia or increased mucus secretion on the gills, as both would limit the transfer of oxygen, and both have been observed.

This study examined the ability of acidic and neutral/alkaline fractions of a methanolic extract from giant reed ( Arundo donax ) and of two of its constituents, gramine and skatole, to inhibit growth of the ichthyotoxic golden alga (Prymnesium parvum ) in batch culture. For this study, growth suppression was defined as inhibition of maximum cell density, algicidal activity as early occurrence of negative growth, and algistatic activity as lack of net growth. The acidic fraction did not affect algal growth. The neutral/alkaline fraction showed growth-suppressing and algicidal activities but no signs of algistatic activity – namely, cells in cultures surviving a partial-algicidal exposure concentration (causing transient negative growth) were later able to initiate positive growth but at higher concentrations, algicidal activity was full and irreversible. Gramine suppressed growth more effectively than skatole and at the highest concentration tested, gramine also showed partial-algicidal and algistatic activity. While the partial-algicidal activities of the neutral/alkaline fraction and of gramine were short-lived (≤6 days) and thus may share similar mechanisms, algistatic activity was unique to gramine and persisted for >3 weeks. Given gramine’s reported concentration in the neutral/alkaline fraction, its corresponding level of algicidal activity is much lower than the fraction’s suggesting the latter contains additional potent algicides. Inhibition of maximum cell density by all test compounds was associated with reductions in exponential growth rate, and in the case of the neutral/alkaline fraction and gramine also reductions in early (pre-exponential) growth. These results indicate that giant reed is a potential source of natural products to control golden alga blooms. Giant reed is an invasive species in North America, thus also providing incentive for research into strategies to couple management efforts for both species. [ABSTRACT FROM AUTHOR]

Prymnesium parvumblooms result in fish kills around the world and are devastating to fish hatcheries, where few management tools are available. Current control strategies include algaecides, nutrient management, and flocculation, which are moderately effective at best and can be toxic to nontarget organisms. A relatively new type of medium, registered by the U.S. Environmental Protection Agency for the control of fecal coliforms in storm water runoff, was evaluated as a possibleP. parvumcontrol tool. The medium, called Smart Sponge, was designed to absorb petroleum hydrocarbons; a variant, Smart Sponge Plus, is enhanced with antimicrobial properties. It is these antimicrobial properties that we investigated for possible use in algal bloom management. Our objective was to evaluate the efficacy of this type of medium on the eradication ofP. parvumand its associated toxins, with a view toward advancing toxic algae control strategies.Prymnesium parvumwas passed through columns of the filter medium. Algal cell counts and visual observations were used to assess mortality; fish bioassays were conducted to assess toxicity. Smart Sponge Plus successfully killed the algae, although toxins were released during filtration. After filtration, 87–100% algal removal was achieved, with the variability potentially being related to cell density at the initiation of the test. Smart Sponge was also successful in reducing associated the toxicity ofP. parvum, as was a charcoal medium. Smart Sponge Plus shows promise for use in the management of golden algal blooms by reducing cell density and should be further evaluated in hatchery and field settings. Received August 28, 2016; accepted February 13, 2017 Published online May 22, 2017 [ABSTRACT FROM AUTHOR]

Salinity (5–30) effects on golden alga growth were determined at a standard laboratory temperature (22 °C) and one associated with natural blooms (13 °C). Inoculum-size effects were determined over a wide size range (100–100,000 cells ml −1 ). A strain widely distributed in the USA, UTEX-2797 was the primary study subject but another of limited distribution, UTEX-995 was used to evaluate growth responses in relation to genetic background. Variables examined were exponential growth rate ( r ), maximum cell density (max-D) and, when inoculum size was held constant (100 cells ml −1 ), density at onset of exponential growth (early-D). In UTEX-2797, max-D increased as salinity increased from 5 to ∼10–15 and declined thereafter regardless of temperature but r remained generally stable and only declined at salinity of 25–30. In addition, max-D correlated positively with r and early-D, the latter also being numerically highest at salinity of 15. In UTEX-995, max-D and r responded similarly to changes in salinity − they remained stable at salinity of 5–10 and 5–15, respectively, and declined at higher salinity. Also, max-D correlated with r but not early-D. Inoculum size positively and negatively influenced max-D and r , respectively, in both strains and these effects were significant even when the absolute size difference was small (100 versus 1000 cells ml −1 ). When cultured under similar conditions, UTEX-2797 grew faster and to much higher density than UTEX-995. In conclusion, (1) UTEX-2797’s superior growth performance may explain its relatively wide distribution in the USA, (2) the biphasic growth response of UTEX-2797 to salinity variation, with peak abundance at salinity of 10–15, generally mirrors golden alga abundance-salinity associations in US inland waters, and (3) early cell density – whether artificially manipulated or naturally attained – can influence UTEX-2797 bloom potential. [ABSTRACT FROM AUTHOR]

Prymnesium parvum is a toxin-producing haptophyte that causes harmful algal blooms globally, leading to large-scale fish kills that have severe ecological and economic implications. For the model haptophyte, Emiliania huxleyi, it has been shown that large dsDNA viruses play an important role in regulating blooms and therefore biogeochemical cycling, but much less work has been done looking at viruses that infect P. parvum, or the role that these viruses may play in regulating harmful algal blooms. In this study, we report the isolation and characterization of a lytic nucleo-cytoplasmic large DNA virus (NCLDV) collected from the site of a harmful P. parvum bloom. In subsequent experiments, this virus was shown to infect cultures of Prymnesium sp. and showed phylogenetic similarity to the extended Megaviridae family of algal viruses. [ABSTRACT FROM AUTHOR]

Control of harmful algae in the coves or bays of larger water bodies could be accomplished by hydraulic flushing with algae-free water. This suggestion is examined with a mathematical model of a harmful algal population, parameterized to represent the toxic haptophyte Prymnesium parvum , and its limiting nutrient. A small cove with a hydraulic storage zone and longitudinal advection and dispersion is coupled to a larger lake where ongoing or transient blooms serve as a source for the algal population. This population is transported upstream by dispersion and flushed downstream by advection. Morphometry and hydraulics represent a lake in Texas where blooms of P. parvum have been problematic. When dispersion and hydraulic storage are low to moderate, available pumping technology is predicted to be capable of suppressing the algal population within a variable portion of the cove, under both steady state and transient conditions. This suppression occurs when temperature-dependent algal growth is low. At temperatures high enough to support more rapid growth, flow augmentation carries a risk of stimulating a bloom under some hydraulic conditions. The model presented here complements similar models without population sources, and contributes to theoretical understanding of population persistence in reservoirs and other flowing-water habitats. [ABSTRACT FROM AUTHOR]

Increasingly over the past century, seasonal fish kills associated with toxic blooms of Prymnesium parvum have devastated aquaculture and native fish, shellfish, and mollusk populations worldwide. Protracted blooms of P. parvum can result in major disturbances to the local ecology and extensive monetary losses. Toxicity of this alga is attributed to a collection of compounds known as prymnesins, which exhibit potent cytotoxic, hemolytic, neurotoxic and ichthyotoxic effects. These secondary metabolites are especially damaging to gill-breathing organisms and they are believed to interact directly with plasma membranes, compromising integrity by permitting ion leakage. Several factors appear to function in the activation and potency of prymnesins including salinity, pH, ion availability, and growth phase. Prymnesins may function as defense compounds to prevent herbivory and some investigations suggest that they have allelopathic roles. Since the last extensive review was published, two prymnesins have been chemically characterized and ongoing investigations are aimed at the purification and analysis of numerous other toxic metabolites from this alga. More information is needed to unravel the mechanisms of prymnesin synthesis and the significance of these metabolites. Such work should greatly improve our limited understanding of the physiology and biochemistry of P. parvum and how to mitigate its blooms.

Blooms of the planktonic alga Prymnesium parvum pose a global threat, causing fish kills worldwide. Early studies on the exposure of fish to P. parvum indicate that toxic effects are related to gill damage. The more strictly defined concept of adverse outcome pathways has been suggested as a replacement for the mode of action in toxicology studies. In this study, rainbow trout (Onchorhyncus mykiss) were exposed to P. parvum. During exposure, oxygen consumption was determined by respirometry, and ventilation and coughing rate were determined via video surveillance. Per breath oxygen consumption was calculated to assess the ventilation effort to obtain a unit of oxygen. A second experiment monitored fish behavior to assess recovery. The results indicated that oxygen consumption initially increased, but on average fell below the standard oxygen consumption at 70% relative exposure. Being a function of ventilation frequency and oxygen consumption, the per breath oxygen consumption decreased throughout exposure. Behavioral results determined that short-term P. parvum exposure subsequently caused the exposed fish to seek flow refuge immediately and to a greater extent than unexposed fish. The adverse outcome pathway of P. parvum on rainbow trout is that P. parvum acts as a gill irritant resulting in non-recoverable respiratory failure.

Bioassays using cultures of the toxic haptophyte Prymnesium parvum and the ciliate Cyclidium sp. as prey were conducted to test the effect of pH (range = 6.5 – 8.5), salinity (range = 1.50 – 7.50‰), and a combination of pH and salinity on the toxicity of P. parvum. pH had a significant effect on P. parvum toxicity. Toxicity was rapidly (within 24 hr) induced by increasing pH of the medium, or reduced by lowering pH. Conversely, lowering salinity reduced toxicity, albeit less effectively compared to pH, and P. parvum cells remained toxic at the lowest values tested (1.50‰ at pH 7.5). An additional effect between pH and salinity was also observed: low salinity combined with low pH led to not only decreased toxicity, but also resulted in lower P. parvum growth rates. Such effects of pH and salinity on P. parvum growth and toxicity provide insight into the environmental factors supporting community dominance and toxic blooms of the alga. [ABSTRACT FROM AUTHOR]