Harmful Blooms Research Articles

Perturbations in a pelagic food web during the NE Pacific Large Marine Heatwave and persistent harmful diatom blooms

Perturbations in a pelagic food web during the NE Pacific Large Marine Heatwave and persistent harmful diatom blooms

Results of studies of harmful bloom microalgae and their habitat conditions in the coastal zone of the Avachinsky Gulf (Kamchatka, Pacifi c Ocean) in 2023

Results of studies of harmful bloom microalgae and their habitat conditions in the coastal zone of the Avachinsky Gulf (Kamchatka, Pacifi c Ocean) in 2023

Magnetic recyclable chitosan-graphene immobilized microcystinase A: Removal of microcystins from harmful microcystis blooms

Harmful Microcystis blooms and microcystins have become a major hidden threat to the safety of the water environment. The application of enzymatic degradation of microcystins has been severely limited by the complex environment. In this study, chitosan-graphene (CG), prepared from green biomass, was employed as matrix material, loaded with 100–200 nm Fe3O4 nanoparticles (MCG) and immobilized microcystinase A (MlrA@MCG). The preparation of MlrA@MCG was characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, vibrating sample magnetometer and fluorescence labelling. The results of the activity analysis demonstrated that MlrA@MCG exhibited superior degradation activity for MCs, as well as enhanced heat and alkaline resistance in comparison to free MlrA. Furthermore, MlrA@MCG can be recovered simply by means of a magnetic field, and its activity remains at 48.6 % after 10 repeated uses. More importantly, MlrA@MCG and the degradation products of MC-LR were not found to be cytotoxic to human cells. It is interesting that the immobilization of MlrA resulted in a reduction in the cytotoxicity of MCG. 0.2 U of MlrA@MCG can still degrade MC-LR from 232.64 μg L−1 to 94.39 μg L−1 in water from simulated severe Microcystis blooms within 24 h, showing excellent catalytic activity and stability. The study proposed a secure and efficacious approach for the elimination of microcystins from harmful Microcystis blooms, offering a promising avenue for the improvement of environmental safety.

Effects of nutrient ratios on a newly harmful dinoflagellate Heterocapsa bohaiensis: Evidence from growth, toxicity and transcriptome analyses

Heterocapsa bohaiensis is a newly identified dinoflagellate species that causes harmful blooms in coastal areas in China, Malaysian, and New Caledonian. These blooms have led to substantial economic losses for local aquaculture. Previous studies have mainly focused on understanding the toxicity of H. bohaiensis. However, the causes of H. bohaiensis blooms remain unknown. In this study, we aimed to ascertain nitrogen (N) and phosphorus (P) requirements for the growth and reproduction of H. bohaiensis. Additionally, we sought to understand the functional mechanisms by comparing the transcriptomes of H. bohaiensis under nutrient-limited conditions and control conditions. The results revealed a wide range of acceptable N:P ratios for H. bohainensis, attributed to a mechanism involving nutrient storage, which allowed H. bohainensis to sustain its growth even when either nitrate or phosphate was depleted. Higher N:P ratios (>27.5) were more conducive to the growth of H. bohainensis than f/2 medium or low ratios, which is related to the N:P ratios absorbed by H. bohainensis. The toxicity of H. bohainensis was significantly enhanced in N-limited or P-limited states. These findings underscore the significance of the physiological metabolism of H. bohainensis in adapting to environmental stresses induced by human activities and establishing the dominance of blooms.

Deactivation of harmful green tide using Ag/SiO2 and Ag/Al2O3 coatings on low-density porous materials

Nowadays harmful bloom tides affect greatly the economy of coastal states. For this reason, the present communication reports on a practical method for synthesizing SiO2 and γ-alumina nanospheres, immobilized by sonochemistry on low-density porous foams and perlite granules, as a solution to this problem. A biostatic AgNP effect was incorporated into both materials, achieving AgSi and AgAl. The green-tide inactivation was performed by using Tetraselmis suecica under aqueous conditions. AgAl/FWGS displayed the best inactivation efficiency performance (94 %). Additionally, foams have significant buoyancy and are easy to handle, being an option for T. suecica inactivation for their easy recovering.

Seasonal changes in the protist communities of Hakodate Bay, southern Hokkaido, from 2020 to 2022

Hakodate Bay at the southern end of Hokkaido experiences physical and chemical environmental changes in the adjacent Tsugaru Strait. Harmful algal blooms have occurred since 2015. However, information on the response of protist community composition, photosynthetic activity to environmental variables or the mechanisms causing harmful blooms in the Hakodate Bay is lacking. We investigated the seasonal changes in the protist community using weekly sampling to reveal the relationship between the protist community and environmental variables in the Hakodate Bay. Based on cluster analysis, six groups were identified: Winter, Spring, Late Spring, Summer, Benthic, and Karenia. High Fv/Fm was seen in the Summer, Benthic and Spring groups supported by high nutrients, warm temperature and sufficient irradiance. From the Winter to Spring group, a species transition from low-temperature-adapting Thalassiosira spp. to Chaetoceros spp. was found. The Summer group comprised high salinity-tolerant species (the diatom Leptocylindrus danicus and dinoflagellate Prorocentrum spp.) because of high fluctuations in salinity due to precipitation. The other groups (Late Spring, Benthic, and Karenia) randomly filled the spaces between the three groups. The dinoflagellate Scrippsiella spp. was dominant in the Late Spring group because of accumulation by wind-driven currents. Because a strong relationship between benthic species and wind speed was exhibited, the Benthic group comprised benthic diatoms released into the water by mixing. The Karenia group was observed only from late August 2021 to early January 2022, when higher ammonium and lower light conditions (i.e., cloudy conditions) were detected. Owing to environmental conditions, diatom growth was restricted by low light intensity, whereas that of Karenia mikimotoi increased by taking advantage of the abundant nutrients. Seasonal changes in the protist community of the Hakodate Bay can generally be explained by temperature; however, in the short term (1–2 weeks), changes were also influenced by meteorological conditions (solar radiation, wind, and precipitation).

Long-Read Sequencing Unlocks New Insights into the Amphidinium carterae Microbiome.

Dinoflagellates are one of the largest groups of marine microalgae and exhibit diverse trophic strategies. Some dinoflagellates can produce secondary metabolites that are known to be toxic, which can lead to ecologically harmful blooms. Amphidinium carterae is one species of dinoflagellate that produces toxic compounds and is used as a model for dinoflagellate studies. The impact of the microbiome on A. carterae growth and metabolite synthesis is not yet fully understood, nor is the impact of bacterial data on sequencing and assembly. An antibiotic cocktail was previously shown to eliminate 16S amplification from the dinoflagellate culture. Even with drastically reduced bacterial numbers during antibiotic treatment, bacterial sequences were still present. In this experiment, we used novel Nanopore long-read sequencing techniques on A. carterae cultures to assemble 15 full bacterial genomes ranging from 2.9 to 6.0 Mb and found that the use of antibiotics decreased the percentage of reads mapping back to bacteria. We also identified shifts in the microbiome composition and identified a potentially deleterious bacterial species arising in the absence of the antibiotic treatment. Multiple antibiotic resistance genes were identified, as well as evidence that the bacterial population does not contribute to toxic secondary metabolite synthesis.

Influence of multi-stressor combinations of pCO2, temperature, and salinity on the toxicity of Heterosigma akashiwo (Raphidophyceae), a fish-killing flagellate.

Climate change and global warming have led to more frequent harmful algal blooms in the last decade. Among these blooms, Heterosigma akashiwo, a golden-brown phytoflagellate, is one of the 40 species with a high potential to form harmful blooms, leading to significant fish mortality. Climate change leads to rising atmospheric and ocean temperatures. These changes, along with altered rainfall patterns and meltwater input, can cause fluctuations in ocean salinity. Elevated atmospheric carbon dioxide (CO2) levels increase water acidity as oceans absorb CO2. This study investigated the effects of temperature, salinity, and CO2 levels on lipid production, hemolytic activity, and toxicity of H. akashiwo using the design of experiment approach, which can be used to investigate the effect of two or more factors on the same response simultaneously in a precise manner with fewer experiments and materials but in a larger region of the factor space. The lipid content was measured using a high-throughput Nile Red method, and the highest level of lipid content was detected at 25°C, a salinity of 30, and a CO2 concentration of 400 ppm. Hemolytic activity was assessed using rabbit blood erythrocytes in a 96-well plate, and the optimal conditions for achieving the highest hemolytic activity were determined at 15°C, a salinity of 10, and a CO2 concentration of 400 ppm. As the chemical structure of the toxin is not known, we used the toxicity against the cell line RTgill-W1 as the cell toxicity proxy. The maximum toxicity was identified at 15°C, a salinity of 10, and a CO2 level of 700 ppm.

Kinetics and Mechanism of Cyanobacteria Cell Removal Using Biowaste-Derived Activated Carbons with Assessment of Potential Human Health Impacts.

Harmful cyanobacteria blooms and the escalating impact of cyanotoxins necessitates the effective removal of cyanobacteria from water ecosystems before they release cyanotoxins. In this study, cyanobacteria removal from water samples taken from the eutrophic Aleksandrovac Lake (southern Serbia) was investigated. For that purpose, novel activated carbons derived from waste biomass-date palm leaf stalk (P_AC), black alder cone-like flowers (A_AC), and commercial activated carbon from coconut shell (C_AC) as a reference were used. To define the best adsorption conditions and explain the adsorption mechanism, the influence of contact time, reaction volume, and adsorbent mass, as well as FTIR analysis of the adsorbents before and after cyanobacteria removal, were studied. The removal efficiency of P_AC and A_AC achieved for the applied concentration of 10 mg/mL after 15 min was ~99%, while for C_AC after 24 h was only ~92% for the same concentration. To check the safety of the applied materials for human health and the environment, the concentrations of potentially toxic elements (PTEs), the health impact (HI) after water purification, and the toxicity (MTT and Comet assay) of the materials were evaluated. Although the P_AC and A_AC achieved much better removal properties in comparison with the C_AC, considering the demonstrated genotoxicity and cytotoxicity of the P_AC and the higher HI value for the C_AC, only the A_AC was further investigated. Results of the kinetics, FTIR analysis, and examination of the A_AC mass influence on removal efficiency indicated dominance of the physisorption mechanism. Initially, the findings highlighted the superior performance of A_AC, with great potential to be globally commercialized as an effective cyanobacteria cell adsorbent.

Progress in Research on Microplastic Prevalence in Tropical Coastal Environments: A Case Study of the Johor and Singapore Straits

Microplastics are contaminants in marine ecosystems, posing great threats to biota and human health. In this work, we provide an overview of the progress made in understanding microplastic prevalence in tropical coastal environments, focusing on the Johor and the Singapore Straits as a case study. We examine the sources, distribution, transport, and ecological impact of microplastic pollution in this region through a systematic review. All papers relating to marine microplastics in Singapore’s sand and benthic sediments, seawater, and marine biota were used for analysis, from 2004 to 2023. In addition, we discuss the influence of envi-ronmental factors such as coastal morphology and anthropogenic activities on patterns of microplastic accumulation. We emphasize that microplastic pollution is more prevalent along the eutrophic Johor Strait compared to the Singapore Strait due to hydrological conditions. Rainfall is also a key factor that influences mi-croplastic abundance during the monsoon seasons. Furthermore, the bacterial and plankton assemblages of organisms on microplastic surfaces are diverse, with eutrophic waters enhancing the diversity of organisms on microplastic surfaces. Novel harmful cyanobacteria and bloom species of phytoplankton were also found on microplastic surfaces. By synthesizing existing research findings and highlighting regional characteristics, this paper contributes to ongoing efforts to mitigate microplastic pollution in tropical regions.

Monitoring Harmful Algal Blooms and Water Quality Using Sentinel-3 OLCI Satellite Imagery with Machine Learning

Cyanobacterial harmful algal blooms release toxins and form thick blanket layers on the water surface causing widespread problems, including serious threats to human health, water ecosystem, economics, and recreation. To identify the potential drivers for the bloom, there is a need for extensive observations of the water sources with bloom occurrences. However, the traditional methods for monitoring water sources, such as collection of point ground samples, have proven limited due to spatial and temporal variability of water resources, and the cost associated with collecting samples that accurately represent this variability. These limitations can be addressed through the use of high-frequency satellite data. In this study, we explored the use of Random Forest (RF), which is one of the widely used machine learning architectures, to evaluate the performance of Sentinel-3 OLCI (Ocean and Land Color Imager) images in predicting bloom proxies in the western region of Lake Erie. The sixteen available bands of Sentinel-3 images were used as the predictor variables, while four proxies of the cyanobacterial masses, including Chlorophyll-a, Microcystin, Phycocyanin, and Secchi-depth, were considered as response variables in the RF models, with one RF model per proxy. Each of the proxies comes with a unique set of traits that can help with bloom detection. Among four RF models, the model for Chlorophyll-a performed the best with R2 = 0.55 and RMSE = 20.84 µg/L, while R2 performance for the rest of the other proxies was less than 0.5. This is because Chlorophyll-a is the most dominant and optically active pigment in water, while Phycocyanin, which is a strong indicator of harmful bloom, is present in low concentrations. Additionally, Microcystin, responsible for bloom toxicity, has limited spectral sensitivity, and Secchi-depth could be influenced by various factors besides blooms, such as colored dissolved organic and inorganic matter. On further examining the relationship between the proxies, Microcystin and Secchi-depth were significantly correlated with Chlorophyll-a, which enhances the usefulness of Chlorophyll-a in accurately identifying the presence of algal blooms.

Marine heatwaves alter competition between the cultured macroalga Gracilariopsis lemaneiformis and the harmful bloom alga Skeletonema costatum

Seaweed cultivation can inhibit the occurrence of red tides. However, how seaweed aquaculture interactions with harmful algal blooms will be affected by the increasing occurrence and intensity of marine heatwaves (MHWs) is unknown. In this study, we run both monoculture and coculture systems to investigate the effects of a simulated heatwave on the competition of the economically important macroalga Gracilariopsis lemaneiformis against the harmful bloom diatom Skeletonema costatum. Coculture with G. lemaneiformis led to a growth decrease in S. costatum. Growth and photosynthetic activity (Fv/Fm) of G. lemaneiformis was greatly reduced by the heatwave treatment, and did not recover even after one week. Growth and photosynthetic activity of S. costatum was also reduced by the heatwave in coculture, but returned to normal during the recovery period. S. costatum also responded to the stressful environment by forming aggregates. Metabolomic analysis suggests that the negative effects on S. costatum were related to an allelochemical release from G. lemaneiformis. These findings show that MHWs may enhance the competitive advantages of S. costatum against G. lemaneiformis, leading to more severe harmful algal blooms in future extreme weather scenarios.

Lake and Atmospheric Heatwaves Caused by Extreme Dust Intrusion in Freshwater Lake Kinneret in the Eastern Mediterranean

The role of dust intrusions in the formation of lake heatwaves has not yet been discussed in previous publications. We investigated a lake heatwave (LHW) and an atmospheric heatwave (AHW) in the freshwater Lake Kinneret in the Eastern Mediterranean: these were caused by an extreme dust intrusion that lasted for a 10-day period (7–17 September 2015). The AHW and LHW were defined as periods of abnormally high air temperature (Tair) and lake surface water temperature (SWT) compared to their 90th percentile thresholds in September. In the daytime, the maximal intensities of AHW and LHW reached 3 °C and 2 °C, respectively. This was despite the pronounced drop in solar radiation due to the dust radiative effect. The satellite SWT retrievals were incapable of representing the abnormally high SWT in the presence of the extreme dust intrusion. Both METEOSAT and MODIS-Terra showed a sharp decrease in the SWT compared to the actual SWT: up to 10 °C in the daytime and up to 15 °C in the nighttime. Such a significant underestimation of the actual SWT in the presence of a dust intrusion should be considered when using satellite data to analyze heatwaves. In the absence of moisture advection, the AHW and LHW were accompanied by an increase of up to 30% in absolute humidity (ρv) over the lake. Being a powerful greenhouse gas, water vapor (characterized by an increased ρv) absorbed most of both the upwelling and downwelling longwave thermal radiation, heating the near-ground atmospheric layer (which is in direct contact with the lake water surface), in the daytime and nighttime. In the nighttime, the maximal intensity of the AHW and LHW reached 4 °C and 3 °C, respectively. Because of the observed steadily increasing dust pollution over the Eastern Mediterranean during the past several decades, we anticipate that dust-related lake heatwaves will intensify adverse effects on aquatic ecosystems such as reducing fishery resources and increasing harmful cyanobacteria blooms.

Microcystins in the benthic food-web of the Sacramento-San Joaquin Delta, California

Harmful cyanobacteria blooms are a growing threat in estuarine waters as upstream blooms are exported into coastal environments. Cyanobacteria can produce potent toxins, one of which—hepatotoxic microcystins (MCs)—can persist and accumulate within the food web. Filter-feeding invertebrates may biomagnify toxins up to 100× ambient concentrations. As such, bivalves can be used as an environmentally relevant and highly sensitive sentinel for MC monitoring. To date there has been little research on cyanotoxin bioaccumulation in estuaries. The Sacramento-San Joaquin Delta (Delta) aquatic food web has undergone a profound change in response to widespread colonization of aquatic invasive species such as Asian clams (Corbicula fluminea) in the freshwater portion of the Delta. These clams are prolific—blanketing areas of the Delta at densities up to 1000 clams/m2 and are directly implicated in the pelagic organism decline of threatened and endangered fishes. We hypothesized that Asian clams accumulate MCs which may act as an additional stressor to the food web and MCs would seasonally be in exceedance of public health advisory levels. MCs accumulation in Delta Asian clams and signal crayfish (Pacifastacus leniusculus) were studied over a two-year period. ELISA and LC-MS analytical methods were used to measure free and protein-bound MCs in clam and crayfish tissues. We describe an improved MC extraction method for use when analyzing these taxa by LC-MS. MCs were found to accumulate in Asian clams across all months and at all study sites, with seasonal maxima occurring during the summer. Although MC concentrations rarely exceeded public health advisory levels, the persistence of MCs year-round still poses a chronic risk to consumers. Crayfish at times also accumulated high concentrations of MCs. Our results highlight the utility of shellfish as sentinel organisms for monitoring in estuarine areas.

Ultrasonic-assisted extraction of total flavonoids from Zanthoxylum bungeanum residue and their allelopathic mechanism on Microcystis aeruginosa

Water eutrophication has emerged as a pressing concern for massive algal blooms, and these harmful blooms can potentially generate harmful toxins, which can detrimentally impact the aquatic environment and human health. Consequently, it is imperative to identify a safe and efficient approach to combat algal blooms to safeguard the ecological safety of water. This study aimed to investigate the procedure for extracting total flavonoids from Z. bungeanum residue and assess its antioxidant properties. The most favorable parameters for extracting total flavonoids from Z. bungeanum residue were a liquid–solid ratio (LSR) of 20 mL/g, a solvent concentration of 60%, an extraction period of 55 min, and an ultrasonic temperature of 80 °C. Meanwhile, the photosynthetic inhibitory mechanism of Z. bungeanum residue extracts against M. aeruginosa was assessed with a particular focus on the concentration-dependent toxicity effect. Z. bungeanum residue extracts damaged the oxygen-evolving complex structure, influenced energy capture and distribution, and inhibited the electron transport of PSII in M. aeruginosa. Furthermore, the enhanced capacity for ROS detoxification enables treated cells to sustain their photosynthetic activity. The findings of this study hold considerable relevance for the ecological management community and offer potential avenues for the practical utilization of resources in controlling algal blooms.

Salinity decline promotes growth and harmful blooms of a toxic alga by diverting carbon flow.

Global climate change intensifies the water cycle and makes freshest waters become fresher and vice-versa. But how this change impacts phytoplankton in coastal, particularly harmful algal blooms (HABs), remains poorly understood. Here, we monitored a coastal bay for a decade and found a significant correlation between salinity decline and the increase of Karenia mikimotoi blooms. To examine the physiological linkage between salinity decreases and K. mikimotoi blooms, we compare chemical, physiological and multi-omic profiles of this species in laboratory cultures under high (33) and low (25) salinities. Under low salinity, photosynthetic efficiency and capacity as well as growth rate and cellular protein content were significantly higher than that under high salinity. More strikingly, the omics data show that low salinity activated the glyoxylate shunt to bypass the decarboxylation reaction in the tricarboxylic acid cycle, hence redirecting carbon from CO2 release to biosynthesis. Furthermore, the enhanced glyoxylate cycle could promote hydrogen peroxide metabolism, consistent with the detected decrease in reactive oxygen species. These findings suggest that salinity declines can reprogram metabolism to enhance cell proliferation, thus promoting bloom formation in HAB species like K. mikimotoi, which has important ecological implications for future climate-driven salinity declines in the coastal ocean with respect to HAB outbreaks.

Understanding filamentous cyanobacteria and their adaptive niches in Lake Honghu, a shallow eutrophic lake

Freshwater lakes globally are witnessing an escalation in the frequency and intensity of cyanobacterial harmful blooms. However, underlying factors influencing the succession or coexistence of cyanobacteria, especially filamentous ones, remain poorly understood. Lake Honghu, a Ramsar Wetland of International Importance with degrading aquatic ecological quality, served as a case study to elucidate the intricate relationship between environmental changes and cyanobacterial dynamics. Our analysis revealed a significant increase in the dominance of filamentous cyanobacteria, marked by high spatiotemporal variability in community structure. This dominance of filamentous diazotrophic cyanobacteria is attributed to a decrease in the ratio of dissolved inorganic nitrogen to total phosphorus and their capacity to utilize organic phosphorus in phosphorus-deficient conditions. Species-specific density variations were linked to diverse environmental factors, with total nitrogen or total phosphorus concentration remaining as a crucial factor influencing dominant cyanobacterial density fluctuations. The dominance of low-temperature-tolerant Aphanizomenon and Pseudanabaena was evident in spring and winter, whereas Dolichospermum and Cylindrospermopsis, which prefer higher temperatures, thrived in summer and autumn. Additionally, non-algal turbidity and heterogeneity can potentially alter the competitive outcome among filamentous cyanobacteria or foster coexistence under conditions of elevated temperatures and nutrient limitation. This study predicts that filamentous cyanobacteria may spread and persist in lakes spanning a wide trophic range. Current findings enhance our comprehension of the dynamic responses exhibited by filamentous bloom-forming cyanobacteria in the face of environmental changes within shallow eutrophic lakes and provide valuable insights for lake managers involved in the remediation of degraded shallow lakes.

Capture and flocculation of toxic cyanobacteria by amphiphilic peptide dendrimers for mitigating harmful blooms

Harmful and toxic cyanobacterial blooms in freshwater constitute critical environmental problems and are becoming more frequent as a consequence of global climate change. One mitigation strategy is flocculation, which could be achieved with treatment by highly efficient, non-toxic, and biodegradable agents. Here, we report two amphiphilic peptide dendrimers (AmPDs), KK2 and KK2K4, for the removal of the toxic and bloom-forming cyanobacterium Microcystis aeruginosa from freshwater. KK2 and KK2K4 are composed of a hydrophobic alkyl chain and a positively charged polylysine dendron of the first and second generation, respectively. Owing to electrostatic interactions with the negatively charged cell surface of M. aeruginosa, KK2 and KK2K4 could quickly capture the cyanobacterial cell population via flocculation at very low concentrations. When combined with the natural clay sepiolite, the two AmPDs were even more efficient in promoting cell flocculation. The most performant system, with 3.0 mg/L KK2K4 and sepiolite clay, could remove 97.1 % of M. aeruginosa within 15 min by forming stable flocs. Remarkably, such a system was able to trap toxin molecules released by cyanobacterial cells, thus limiting its destructive impact on ecosystems. This study demonstrates how self-assembling dendrimer materials can resolve cyanobacterial blooms, providing an innovative solution to this environmental challenge.

Chaotic mixotroph dynamics arise with nutrient loading: Implications for mixotrophy as a harmful bloom forming mechanism

Mixotrophic nutrition, in which organisms combine aspects of heterotrophic and autotrophic nutrition, is a common characteristic amongst the phytoplankton, and especially amongst harmful algae bloom (HAB) species. To explore how the addition of a mixotrophic population influences a theoretical plankton system under different enrichment levels, we employ a previously published numerical plankton model that reproduces seasonal succession dynamics. Through this work we found potential for chaos to occur as the system was enriched. Focusing on occurrence of chaos in the mixotroph population, a novel finding, we conducted a bifurcation analysis which demonstrated a period doubling route to chaos. Further, we demonstrate that the occurrence of chaotic dynamics in the model system is not an artifact of the mixotroph life-history trait values used in our initial simulations, rather chaos was found to occur under a wide range of mixotroph trait value combinations. Through our trait analysis, we also found that regardless of whether or not the system was chaotic for a specific combination of values, variation in the mixotroph population peak population density could be high between consecutive years. These findings have implications that are important for the management of nutrients in aquatic systems and HABs. Results shed light on why it may be difficult to predict the occurrence of mixotrophic HABs based solely on environmental variables, when the year-to-year peak density of the mixotroph is chaotic or highly variable with enrichment. These results also demonstrate how initiation of a mixotrophic HAB might occur with enrichment, due to erratic population spikes, when broadcast allelopathic or toxic chemicals are at low concentrations, a novel bloom initiation mechanism.

Harmful blooms caused by dinoflagellates in the Pacific of Guatemala (2019–2022)

Plankton studies in Guatemala are associated with the history of harmful algal blooms (HAB). An important event was observed in 1987, with 193 human poisonings due to shellfish consumption, of which 22 were lethal. The causative organism was Pyrodinium bahamense var. compressum. This species was reported again in November 2019 in the coastal Guatemalan Pacific. The species reached an abundance of 1 × 104 cells/L. In September 2020, the abundance of the Margalefidinium polykrikoides vegetative stage reached 1.24 × 106 cells/L, and its cysts 1.5 × 106 cells/L. Noctiluca scintillans proliferated (the first quantitatively estimated bloom of this species in Guatemala) in November 2020 and March 2021 (up to 1.2 × 106 cells/L). From January to December 2021, monthly monitoring was carried out in front of the Port of Quetzal at three sites (bottle and 25 μm mesh net samples). In April 2022, 11 cases of humans presenting symptoms of paralytic shellfish poisoning (PSP) were recorded in the western sector of the Guatemalan Pacific, in particular, in the municipality of Tiquisate in the department of Escuintla. From May 3 to 27, 2022, a HAB event caused the death of 4 and the poisoning of 34 humans in the departments near Mexico: Retalhuleu (Champerico), San Marcos (Tilapa) and Escuintla (Tiquisate, Buena Vista and Iztapa). The maximum saxitoxin (STX) concentration was determined in Retalhuleu (14,099 MU/100 g); until 7 July 2022, STX continued to be detected in Tilapa and Tiquisate (1,021 MU/100 g). The P. bahamense cells were observed in the stomach contents of the clam Tagelus sp. (Bivalvia: Solecurtidae).