Towards sustainable coastal management: aerial imagery and deep learning for high-resolution Sargassum mapping.

The massive arrival of pelagic Sargassum on the coasts of several countries of the Atlantic Ocean began in 2011 and to date continues to generate social and environmental challenges for the region. Therefore, knowing the distribution and quantity of Sargassum in the ocean, coasts, and beaches is necessary to understand the phenomenon and develop protocols for its management, use, and final disposal. In this context, the present study proposes a methodology to calculate the area Sargassum occupies on beaches in square meters, based on the semantic segmentation of aerial images using the pix2pix architecture. For training and testing the algorithm, a unique dataset was built from scratch, consisting of 15,268 aerial images segmented into three classes. The images correspond to beaches in the cities of Mahahual and Puerto Morelos, located in Quintana Roo, Mexico. To analyze the results the fß-score metric was used. The results for the Sargassum class indicate that there is a balance between false positives and false negatives, with a slight bias towards false negatives, which means that the algorithm tends to underestimate the Sargassum pixels in the images. To know the confidence intervals within which the algorithm performs better, the results of the f0.5-score metric were resampled by bootstrapping considering all classes and considering only the Sargassum class. From the above, we found that the algorithm offers better performance when segmenting Sargassum images on the sand. From the results, maps showing the Sargassum coverage area along the beach were designed to complement the previous ones and provide insight into the field of study.

Allelopathic Effect of a Chilean Strain of Karenia selliformis (Gymnodiniales, Dinoflagellata) on Phytoplankton Species.

Blooms of the dinoflagellate Karenia selliformis in Chile, often associated with massive fish kills, have been noted alongside other species from the Kareniaceae family, such as Karenia spp. and Karlodinium spp. However, the potential allelopathy impact of Chilean K. selliformis on other phytoplankton species remains unexplored. Here, we assessed the allelopathic effects of cell-free exudates from a Chilean K. selliformis strain on six phytoplankton strains representing diverse microalgal groups. The findings of these experiments offer valuable insights into the varied responses of both non-toxic and toxic microalgae to allelochemicals produced by a toxic microalga, showcasing the intricate and multifaceted nature of allelopathic interactions in microalgal communities. The study revealed species-dependent effects, with variable response in cell growth, photosynthetic efficiency (i.e., Fv/Fm), and intracellular reactive oxygen species (ROS) production. While certain strains exhibited significant growth inhibition in response to the allelochemicals, others demonstrated no apparent effect on cell proliferation, indicating varying sensitivity to specific allelochemicals or potentially distinct detoxification mechanisms. Similarly, the diverse effects on Fv/Fm highlight the complexity of allelopathic interactions, with some species showing reduced efficiency without alterations in intracellular ROS production, while others displayed increased ROS production alongside impaired photosynthesis.

Cyanopeptides occurrence and diversity in a Brazilian tropical reservoir: Exploring relationships with water quality.

Microcystins (MCs) are a class of toxic secondary metabolites produced by some cyanobacteria strains that endanger aquatic and terrestrial organisms in various freshwater systems. Although patterns in MC occurrence are being recognized, divergences in the global data still hamper our ability to predict the toxicity of cyanobacterial blooms. This study aimed (i) to determine the dynamics of MCs and other cyanopeptides in a tropical reservoir, (ii) to investigate the correlation between peptides and potential cyanotoxin producers (iii) identifying the possible abiotic factors that influence the peptides. We analyzed, monthly, eight MC variants (MC-RR, -LA, -LF, -LR, -LW, -YR, [D-Asp3]-RR and [D-Asp3]-LR) and other peptides in 47 water samples collected monthly, all season long, from two sampling sites in a tropical eutrophic freshwater reservoir, in southeastern Brazil. The cyanopeptides were assessed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The biomass of potential cyanobacterial producers and water quality variables were measured. MCs were detected in both sampling sites year-round; the total MC concentration varied from 0.21 to 4.04 µg L-1, and three MC variants were identified and quantified (MC-RR, [D-Asp3]-RR, -LR). Additionally, we identified 28 compounds belonging to three other cyanopeptide classes: aeruginosin, microginin, and cyanopeptolin. As potential MC producers, Microcystis spp. and Dolichospermum circinalis were dominant during the study, representing up to 75% of the total phytoplankton. Correlational and redundancy analysis suggested positive effects of dissolved oxygen, nitrate, and total phosphorus on MC and microginins concentration, while water temperature appeared to favor aeruginosins. A comparison between our results and historical data showed a reduction in total phosphorus and cyanobacteria, suggesting increased water quality in the reservoir. However, the current MC concentrations indicate a rise in cyanobacterial toxicity over the last eight years. Moreover, our study underscores the pressing need to explore cyanopeptides other than MCs in tropical aquatic systems.

Detection of harmful algal blooms from satellite-based inherent optical properties of the ocean in Paracas Bay - Peru.

Harmful algal bloom (HAB) events in front of Pisco River, inside Paracas Bay and Lagunillas inlet on the southern coast of Peru was identified from a satellite index (IOPifa) generated with daily high-resolution satellite data of phytoplankton absorption (aphy,GIOP) and non-algal detrital material plus CDOM (adCDOM,GIOP) from the Generalized Inherent Optical Properties (GIOP) model of Modis-Aqua, Viirs-Snpp and Viirs-Jpss1 satellites were used. Phytoplankton density field data sampling from HAB's monitoring programs of IMARPE of 2018 and 2019 were used to validate and identify the extent and spatio-temporal variability of these events. The satellite index (IOPifa) identified for Modis-Aqua 9 active HABs, 8 events in final conditions and 6 events that do not represent HAB conditions, while for Viirs-Snpp found 14 active HABs, 7 events in decaying bloom conditions and 13 events that do not represent HABs; and for Viirs-Jpss1 the index identified 7 active events, 14 in final bloom conditions and 6 that do not represent HABs conditions. The one-factor anova model was applied (p-value = 0.32 > 0.05), indicating that there is no evidence of a difference in the population means of the indices for each sensor. Subsequently, the pairwise multiple comparisons analysis with a 95 % confidence level of Tukey's test confirmed that there are no significant differences in the satellite index value, the differences could be associated with the spectral characteristics of the cell density of the species community and the oceanographic and environmental conditions. The spatial overlap between the in situ harmful algal blooms areas and the calculated satellite index, shows the capacity of the IOP satellite data for the HABs detection. However, it was also evidenced that some HAB events with high phytoplankton cell density had low IOPifa values, while other events with lower cell density were easily identified by the satellite index. This would indicate the ability of the ocean inherent optical properties to differentiate the phytoplankton types that cause algal blooms.

Temporal and spatial variation in hydrogen sulfide (H2S) emissions during holopelagic Sargassum spp. decomposition on beaches.

BACKGROUND: Since 2011, over 30 tropical Atlantic nations have experienced substantial landings of holopelagic Sargassum spp. Its decomposition results in the production of hydrogen sulfide (H2S), which, in elevated concentrations, can pose a threat to human health. This study aims to enhance our understanding of the temporal and spatial variability in H2S emissions during the decomposition of Sargassum on beaches. The primary objective is to assess potential exposure risks for local populations, tourists, and cleanup workers. METHODS: H2S levels were monitored using a SENKO sensor (SGTP-H2S; limit of detection 0.1-100 ppm; resolution 0.1 ppm) at four distances from Sargassum accumulation points of (0, 10, 30, and 40 m) in Puerto Morelos, Mexico, during 2022 and 2023. RESULTS: Elevated concentrations of H2S were detected beneath the Sargassum piles, with 23.5% of readings exceeding 5 ppm and occasional spikes above 100 ppm. Above the piles, 87.3% of the measurements remained below 2 ppm, and the remainder fell between 2.1 and 5.2 ppm. At 10 m from the shoreline, 90% of measurements registered below 0.1 ppm, and the remaining 10% were below 2 ppm. Readings at 30 and 40 m consistently recorded levels below 0.1 ppm. H2S concentrations positively correlated with Sargassum pile height, the temperature beneath the piles, and wind speed. CONCLUSIONS: Our findings suggest no immediate and significant exposure risk for residents or tourists. However, Sargassum cleanup workers face a higher exposure risk, potentially encountering concentrations above 5 ppm for nearly one-fourth of the working time.

Gambierdiscus species diversity and community structure in St. Thomas, USVI and the Florida Keys, USA.

Ciguatera Poisoning (CP) is a widespread and complex poisoning syndrome caused by the consumption of fish or invertebrates contaminated with a suite of potent neurotoxins collectively known as ciguatoxins (CTXs), which are produced by certain benthic dinoflagellates species in the genera Gambierdiscus and Fukuyoa. Due to the complex nature of this HAB problem, along with a poor understanding of toxin production and entry in the coral reef food web, the development of monitoring, management, and forecasting approaches for CP has lagged behind those available for other HAB syndromes. Over the past two decades, renewed research on the taxonomy, physiology, and toxicology of CP-causing dinoflagellates has advanced our understanding of the species diversity that exists within these genera, including identification of highly toxic species (so called "superbugs") that likely contribute disproportionately to ciguatoxins entering coral reef food webs. The recent development of approaches for molecular analysis of field samples now provide the means to investigate in situ community composition, enabling characterization of spatio-temporal species dynamics, linkages between toxic species abundance and toxin flux, and the risk of ciguatoxin prevalence in fish. In this study we used species-specific fluorescent in situ hybridization (FISH) probes to investigate Gambierdiscus species composition and dynamics in St. Thomas (USVI) and the Florida Keys (USA) over multiple years (2018-2020). Within each location, samples were collected seasonally from several sites comprising varying depths, habitats, and algal substrates to characterize community structure over small spatial scales and across different host macrophytes. This approach enabled the quantitative determination of communities over spatiotemporal gradients, as well as the selective enumeration of species known to exhibit high toxicity, such as Gambierdiscus silvae. The investigation found differing community structure between St. Thomas and Florida Keys sites, driven in part by differences in the distribution of toxin-producing species G. silvae and G. belizeanus, which were present throughout sampling sites in St. Thomas but scarce or absent in the Florida Keys. This finding is significant given the high toxicity of G. silvae, and may help explain differences in fish toxicity and CP incidence between St. Thomas and Florida. Intrasite comparisons along a depth gradient found higher concentrations of Gambierdiscus spp. at deeper locations. Among the macrophytes sampled, Dictyota may be a likely vector for toxin transfer based on their widespread distribution, apparent colonization by G. silvae, and palatability to at least some herbivore grazers. Given its ubiquity throughout both study regions and sites, this taxa may also serve as a refuge, accumulating high concentrations of Gambierdiscus and other benthic dinoflagellates, which in turn can serve as source populations for highly palatable and ephemeral habitats nearby, such as turf algae. These studies further demonstrate the successful application of FISH probes in examining biogeographic structuring of Gambierdiscus communities, targeting individual toxin-producing species, and characterizing species-level dynamics that are needed to describe and model ecological drivers of species abundance and toxicity.

Diversity and toxicity of the planktonic diatom genus Pseudo-nitzschia from coastal and offshore waters of the Southeast Pacific, including Pseudo-nitzschia dampieri sp. nov.

To expand knowledge of Pseudo-nitzschia species in the Southeast Pacific, we isolated specimens from coastal waters of central Chile (36°S-30°S), the Gulf of Corcovado, and the oceanic Robinson Crusoe Island (700 km offshore) and grew them into monoclonal strains. A total of 123 Pseudo-nitzschia strains were identified to 11 species based on sequencing of the ITS region of the nuclear rDNA and on ultrastructural and morphometric analyses of the frustule in selected representatives of each clade: P. australis, P. bucculenta, P. cf. chiniana, P. cf. decipiens, P. fraudulenta, P. hasleana, P. multistriata, P. plurisecta, P. cf. sabit, the new species P. dampieri sp. nov., and one undescribed species. Partial 18S and 28S rDNA sequences, including the hypervariable V4 and D1-D3 regions used for barcoding, were gathered from representative strains of each species to facilitate future metabarcoding studies. Results showed different levels of genetic, and at times ultrastructural, diversity among the above-mentioned entities, suggesting morphological variants (P. bucculenta), rapidly radiating complexes with ill-defined species boundaries (P. cf. decipiens and P. cf. sabit), and the presence of new species (P. dampieri sp. nov., Pseudo-nitzschia sp. 1, and probably P. cf. chiniana). Domoic acid (DA) was detected in 18 out of 82 strains tested, including those of P. australis, P. plurisecta, and P. multistriata. Toxicity varied among species mostly corresponding to expectations from previous reports, with the prominent exception of P. fraudulenta; DA was not detected in any of its 10 strains tested. In conclusion, a high diversity of Pseudo-nitzschia exists in Chilean waters, particularly offshore.

Students' foundational understanding of chemical reaction in the forensic science bachelor's degree program at the National Autonomous University of Mexico.

OBJECTIVE: To compare the understanding of the concept of chemical reaction-as operationalized by Bloom's taxonomy of cognitive levels-of students in forensic science bachelor's degree with that achieved by students majoring in chemistry, as a prerequisite for future professional collaboration and communication. MATERIALS AND METHODS: Using previously validated and published tests developed to assess students' knowledge, comprehension, and application of the concept of chemical reaction, we explored how conceptual understanding developed in students enrolled in (a) a forensic science degree program in a Mexican public university and in (b) chemistry undergraduate programs offered by the same university, and whether both groups achieved comparable attainment levels. FINDINGS AND IMPLICATIONS: Despite receiving considerably less chemical instruction, forensic science students achieved comparable levels of conceptual understanding of chemical reaction to those exhibited by chemistry students. This finding is encouraging because it might mean that future forensic scientists could graduate with a solid foundation of chemical knowledge. More research, particularly on the learning of other key concepts, will be needed to verify these initial findings.

Monitoring bacterial composition and assemblage in the Gulf of Corcovado, southern Chile: Bacteria associated with harmful algae.

Harmful Algal Blooms (HABs) have caused damage to the marine environment in Isla San Pedro in the Gulf of Corcovado, Chile. While rising water temperature and artificial eutrophication are the most discussed topics as a cause, marine bacteria is a recent attractive parameter as an algal bloom driver. This study monitored algal and bacterial compositions in the water of Isla San Pedro for one year using microscopy and 16S rRNA metabarcoding analysis, along with physicochemical parameters. The collected data were analyzed with various statistical tools to understand how the particle-associated bacteria (PA) and the free-living (FL) bacteria were possibly involved in algal blooms. Both FL and PA fractions maintained a stable bacterial composition: the FL fraction was dominated by Proteobacteria (α-Proteobacteria and γ-Proteobacteria), and Cyanobacteria dominated the PA fraction. The two fractions contained equivalent bacterial taxonomic richness (c.a. 8,000 Operational Taxonomic Units) and shared more than 50% of OTU; however, roughly 20% was exclusive to each fraction. The four most abundant algal genera in the Isla San Pedro water were Thalassiosira, Skeletonema, Chaetoceros, and Pseudo-nitzchia. Statistical analysis identified that the bacterial species Polycyclovorans algicola was correlated with Pseudo-nitzschia spp., and our monitoring data recorded a sudden increase of particle-associated Polycyclovorans algicola shortly after the increase of Pseudo-nitzschia, suggesting that P. algicola may have regression effect on Pseudo-nitzschia spp. The study also investigated the physicochemical parameter effect on algal-bacterial interactions. Oxygen concentration and chlorophyll-a showed a strong correlation with both FL and PA bacteria despite their assemblage differences, suggesting that the two groups had different mechanisms for interacting with algal species.

Geochemical behavior of rare earth elements (REE) in urban reservoirs: the case of Funil Reservoir, Rio de Janeiro State, Brazil.

Rare earth elements (REE) have unique chemical properties, which allow their use as geochemical tracers. In this context, the present study aims to assess the role of Funil Reservoir on REE biogeochemical behavior. We collected water samples upstream of the reservoir (P-01) in the city of Queluz, inside the reservoir (P-02), and downstream of Funil Reservoir (P-03) in the city of Itatiaia, RJ. In the field, physicochemical parameters were measured using a probe (pH, temperature, electrical conductivity, and dissolved oxygen). In the laboratory, water samples were filtered (0.45 µm) and properly packed until chemical analysis. Chlorophyll a concentrations were determined by a spectrophotometric method and suspended particulate matter (SPM) by a gravimetric method. Ionic concentrations were determined by ion chromatography technique and REE concentrations were determined by ICP-MS. Chlorophyll a concentrations were higher in Funil Reservoir. Ionic concentrations in Queluz (P-01) suggest anthropic contamination. The sum of REE in the dissolved fraction ranged from 2.12 to 12.22 µg L-1. A positive anomaly of La in Queluz indicates anthropic contamination. The observed patterns indicate that Funil Reservoir acts as a biogeochemical barrier, modifying the fluvial transport of REE. Nonetheless, another factor that probably influences REE behavior is the algal bloom that occurs in reservoirs during the rainy season. The seasonal behavior of algae can influence REE biogeochemistry through the incorporation and release of trace metals.

A New Bioassay for the Detection of Paralytic and Amnesic Biotoxins Based on Motor Behavior Impairments of Zebrafish Larvae.

The global concern about the increase of harmful algal bloom events and the possible impacts on food safety and aquatic ecosystems presents the necessity for the development of more accessible techniques for biotoxin detection for screening purposes. Considering the numerous advantages that zebrafish present as a biological model and particularly as a toxicants sentinel, we designed a sensitive and accessible test to determine the activity of paralytic and amnesic biotoxins using zebrafish larvae immersion. The ZebraBioTox bioassay is based on the automated recording of larval locomotor activity using an IR microbeam locomotion detector, and manual assessment of four complementary responses under a simple stereoscope: survival, periocular edema, body balance, and touch response. This 24 h acute static bioassay was set up in 96-well microplates using 5 dpf zebrafish larvae. For paralytic toxins, a significant decrease in locomotor activity and touch response of the larvae was detected, allowing a detection threshold of 0.1-0.2 µg/mL STXeq. In the case of the amnesic toxin the effect was reversed, detecting hyperactivity with a detection threshold of 10 µg/mL domoic acid. We propose that this assay might be used as a complementary tool for environmental safety monitoring.

Remote sensing for mapping algal blooms in freshwater lakes: a review.

A large number of freshwater lakes around the world show recurring harmful algal blooms, particularly cyanobacterial blooms, that affect public health and ecosystem integrity. Prediction, early detection, and monitoring of algal blooms are inevitable for the mitigation and management of their negative impacts on the environment and human beings. Remote sensing provides an effective tool for detecting and spatiotemporal monitoring of these events. Various remote sensing platforms, such as ground-based, spaceborne, airborne, and UAV-based, have been used for mounting sensors for data acquisition and real-time monitoring of algal blooms in a cost-effective manner. This paper presents an updated review of various remote sensing platforms, data types, and algorithms for detecting and monitoring algal blooms in freshwater lakes. Recent studies on remote sensing using sophisticated sensors mounted on UAV platforms have revolutionized the detection and monitoring of water quality. Image processing algorithms based on Artificial Intelligence (AI) have been improved recently and predicting algal blooms based on such methods will have a key role in mitigating the negative impacts of eutrophication in the future.

Satellite assessment of eutrophication hot spots and algal blooms in small and medium-sized productive reservoirs in Uruguay's main drinking water basin.

Intensive agricultural activities favor eutrophication and harmful phytoplankton blooms due to the high export of nutrients and damming of rivers. Productive watersheds used for water purification can have multiple reservoirs with phytoplankton blooms, which constitutes a high health risk. In general, water quality monitoring does not cover small- and medium-sized reservoirs (0.25-100 ha) of productive use due to their large number and location in private properties. In this work, the in situ trophic state of fourteen reservoirs was simultaneously assessed using Sentinel-2 images in the Santa Lucía River Basin, the main drinking water basin in Uruguay. These reservoirs are hypereutrophic (0.18-5.22 mg total P L-1) with high phytoplankton biomasses (2.8-4439 µg chlorophyll-a L-1), mainly cyanobacteria. Based on data generated in situ and Sentinel-2 imagery, models were fitted to estimate satellite Chl-a and transparency in all the basin reservoirs (n = 486). The best fits were obtained with the green-to-red band ratio (560 and 665 nm, R2 = 0.84) to estimate chlorophyll-a and reflectance at 833 nm (R2 = 0.73) to determine transparency. The spatial distribution of the trophic state was explored by spatial autocorrelation and hotspot analysis, and the variation in spatial patterns could be determined prior and subsequent to a maximum cyanobacteria value in water treatment plant intakes. Therefore, reservoirs with greater potential for phytoplankton biomass export were identified. This work provides the first fitted tool for satellite monitoring of numerous reservoirs and strengthens the country's ability to respond to harmful phytoplankton blooms in its main drinking water basin.

Sublethal effect of the toxic dinoflagellate Karlodinium veneficum on early life stages of zebrafish (Danio rerio).

Dinoflagellates of the genus Karlodinium are ichthyotoxic species that produce toxins including karlotoxins and karmitoxins. Karlotoxins show hemolytic and cytotoxic activities and have been associated with fish mortality. This study evaluated the effect of toxins released into the environment of Karlodinium veneficum strain K10 (Ebro Delta, NW Mediterranean) on the early stages of Danio rerio (zebrafish). Extracts of the supernatant of K10 contained the mono-sulfated KmTx-10, KmTx-11, KmTx-12, KmTx-13, and a di-sulfated form of KmTx-10. Total egg mortality was observed for karlotoxin concentration higher than 2.69 µg L-1. For 1.35 µg L-1, 87% of development anomalies were evidenced (all concentrations were expressed as KmTx-2 equivalent). Larvae of 8 days postfertilization exposed to 1.35 µg L-1 presented epithelial damage with 80% of cells in the early apoptotic stage. Our results indicate that supernatants with low concentration of KmTxs produce both lethal and sublethal effects in early fish stages. Moreover, apoptosis was induced at concentrations as low as 0.01 µg L-1. This is of great relevance since detrimental long-term effects due to exposure to low concentrations of these substances could affect wild and cultured fish.

Simulating oligotrophication in a eutrophic shallow lake to assess the effect of periphyton bioreactor on phytoplankton and epipelon.

We evaluated the effects of a periphyton bioreactor on phytoplankton by experimentally simulating oligotrophication in a shallow eutrophic system. The experiment had two 50% diluted treatments with and without a periphyton bioreactor. Sampling was performed on days 6, 9, 12, 15, and 20 of the experimental period. The periphyton bioreactor accumulated biomass (chlorophyll-a, AFDM) and TP during the experimental period. Despite the biomass and TP loss due to periphyton detachment from the substrate after community reaching the algal biomass peak, the gains exceeded the losses, and the net rate was positive for all attributes in the bioreactor. Based on the average, our findings suggest that periphyton bioreactors negatively affected the phytoplankton total biovolume. Cyanobacteria were the most abundant phytoplankton group. However, the periphyton bioreactor caused the biomass loss of the Raphidiopsis raciborskii in phytoplankton. Our results suggest that bioreactor influenced the phytoplankton structure, reducing cyanobacterial biomass, especially Raphidiopsis raciborskii. However, the bioreactor did not reflect a significant increase in the epipelon biomass during the experimental period. We conclude that the periphyton bioreactor has the potential to assist in the maintenance of restored shallow lakes and reservoirs, especially in controlling phytoplankton growth.

Ocorrência de florações de cianobactérias e consequências para a saúde pública no Nordeste do Brasil / Ocurrence of cyanobacterial bloom and consequences for public health in Northeastern Brazil / Ocurrencia de las floraciones de cianobacterias y consecuencias para la salud pública en el Nordeste de Brasil

As florações são resultado de interações entre fatores físicos, químicos e biológicos, sendo caracterizadas pelo crescimento massivo de microrganismos. As proliferações de cianobactérias indicam a deterioração na qualidade da água e podem ser consideradas problemas de saúde pública, devido à capacidade de produção e liberação de toxinas pelas cianobactérias nos ambientes aquáticos, especialmente nos reservatórios de abastecimento. Assim, este trabalho teve como objetivo verificar, a partir de uma revisão de literatura, a ocorrência de florações de cianobactérias e cianotoxinas e os efeitos especialmente para saúde pública. A metodologia utilizada foi revisão narrativa de trabalhos selecionados seguindo os critérios de inclusão. Foi verificada a ocorrência de 74 espécies de cianobactérias, sendo Microcystis aeruginosa e Raphidiopsis raciborskii as predominantes. Espécies potencialmente tóxicas foram encontradas em todas as florações relatadas nos trabalhos realizados na região Nordeste. As florações de cianobactérias ocorreram principalmente em reservatórios da região Nordeste, juntamente com cianotoxinas (microcistinas, cilindrospermopiscina e saxitoxina). Têm sido frequentes florações com cianotoxinas em sistemas aquáticos, ocasionando alterações no ambiente aquático. Essas modificações alcançam diversos níveis tróficos e podem alcançar o homem, sendo problema de saúde pública.

The blooms are the result of interactions between physical, chemical, and biological factors, and are characterized by the explosive growth of microorganisms. The proliferations of cyanobacteria indicate deterioration in quality and can be considered public health problems due to the ability of cyanobacteria to produce and release toxins in aquatic environments, especially in supply reservoirs. Thus, this study aimed to review the literature to verify the occurrence of cyanobacteria and cyanotoxin blooms and the effects especially for public health. The methodology used was narrative review of selected papers according to the inclusion criteria. The occurrence of 74 cyanobacteria species was verified, with Microcystis aeruginosa and Raphidiopsis raciborskii being the predominant ones. Potentially toxic species were found in all blooms studies carried out in the Northeast region. Cyanobacterial blooms were found mainly in reservoirs in the Northeast region, along with cyanotoxins (microcystins, cylindrospermopsin, and saxitoxin). Blooms with cyanotoxins have been frequent in aquatic systems, causing changes in the aquatic environment. These changes reach several trophic levels, and can reach man, being a public health problem.

Las floraciones son el resultado de interacciones entre factores físicos, químicos y biológicos, caracterizadas por el crecimiento explosivo de microorganismos. La proliferación de cianobacterias indica un deterioro de la calidad y puede considerarse un problema de salud pública debido a la capacidad de las cianobacterias de producir y liberar toxinas en ambientes acuáticos, especialmente en los embalses de abastecimiento. Así, este estudio tenía como objetivo revisar la literatura para verificar la ocurrencia de floraciones de cianobacterias y cianotoxina, así como sus efectos especialmente en la salud pública. La metodología utilizada fue la revisión narrativa de los documentos seleccionados de acuerdo con los criterios de inclusión. Se verificó la aparición de 74 especies de cianobacterias, de las cuales Microcystis aeruginosa y Raphidiopsis raciborskii fueron las más predominantes. Se encontraron especies potencialmente tóxicas en todos los estudios de floración realizados en los estados de la región Nordeste de Brasil. Las floraciones de cianobacterias se encontraron principalmente en embalses en la región Nordeste, junto con cianotoxinas (microcistinas, cilindrospermopsinas y saxitoxinas). Ha habido frecuentes floraciones con cianotoxinas en los sistemas acuáticos, causando cambios en el medio acuático. Estos cambios alcanzan varios niveles tróficos y pueden llegar al hombre, siendo un problema de salud pública.

Possible Amazonian contribution to Sargassum enhancement on the Amazon Continental Shelf.

The Amazon Continental Shelf (ACS) has a coastline of ∼1000 km and is situated in a humid equatorial region with two distinct seasons, wet and dry, and two transitional climatic periods. A total of eight oceanographic cruises were conducted to investigate the dynamics of the inorganic nutrients dissolved in the surface layer of the water column of the ACS and their associations with Sargassum blooms. An excess of nitrogen-N* (NH4+ = 0.01-9.30 µmol l-1) was verified through the salinity gradient from the continent to the ACS, mainly during the period of maximum discharge of the Amazon and Tocantins-Pará rivers. The highest NH4+ concentrations coincided with the occurrence of macrophyte (Sargassum sp.) blooms in the mesohaline and oceanic regions. During this period the high values of NH4+ accompany the low values of Sea Surface Salinity (SSS), indicating the advection of the Amazonian plume towards the Caribbean Sea. In the Sargassum belts we observed a N:P ratio = 60:1 during wet period, while outside this region, the N:P ratio was 34:1. According to DIN vs. AOU ratio, we observed that heterotrophic processes prevail over productive processes, mainly in the mesohaline and low salinity regions. Nitrogen concentrations from runoff, mainly from hydrographic basins, showed significant increases in the last decade, mainly due to anthropogenic factors such as agriculture, deforestation, livestock, urban sewage (domestic and industrial), and demographic growth of the population in the Tocantins-Pará Basin. Additionally, associations of diatoms and cyanobacteria provide more nitrogen in the mesohaline and oceanic regions that nourishes Sargassum blooms. Seasonal comparisons (October and April) of Sargassum belts with other studies, indicated that currents play a fundamental role in the transport of these macrophytes from the east edge (Africa) to the west edge (Brazil and French Guiana) towards the Caribbean Sea in the tropical Atlantic.

Increased chlorophyll-a concentration in Barra Bonita reservoir during extreme drought periods.

Climate projections models indicate that longer periods of droughts are expected within the next 100 years in various parts of South America. To understand the effects of longer periods of droughts on aquatic environments, we investigated the response of chlorophyll-a (Chl-a) concentration to recent severe drought events in the Barra Bonita Hydroelectric Reservoir (BBHR) in São Paulo State, Brazil. We used satellite imagery to estimate the Chl-a concentration from 2014 to 2020 using the Slope Index (NRMSE of 18.92% and bias of -0.20 mg m-3). Ancillary data such as precipitation, water level and air temperature from the same period were also used. Drought events were identified using the standardized precipitation index (SPI). In addition, we computed the probability of future drought events. Two periods showed extremely dry conditions: 1) January-February (2014) and 2) April-May (2020). Both periods were characterized by a recurrence probability of 1in every 50 years. The highest correlation was observed between Chl-a concentration and SPI (-0.97) in 2014, while Chl-a had had the highest correlation with water level (-0.59) in 2020. These results provide new insights into the influence of extreme drought events on the Chl-a concentration in the BBHR and their relationship with other climate variables and reservoir water levels. Drought events imply less rainfall, higher temperatures, and atmospheric dryness, and these factors affect evaporation and the water levels in the reservoir.

Microcystin drives the composition of small-sized bacterioplankton communities from a coastal lagoon.

Cyanobacterial blooms affect biotic interactions in aquatic ecosystems, including those involving heterotrophic bacteria. Ultra-small microbial communities are found in both surface water and groundwater and include diverse heterotrophic bacteria. Although the taxonomic composition of these communities has been described in some environments, the involvement of these small cells in the fate of environmentally relevant molecules has not been investigated. Here, we aimed to test if small-sized microbial fractions from a polluted urban lagoon were able to degrade the cyanotoxin microcystin (MC). We obtained cells after filtration through 0.45 as well as 0.22 µm membranes and characterized the morphology and taxonomic composition of bacteria before and after incubation with and without microcystin-LR (MC-LR). Communities from different size fractions (< 0.22 and < 0.45 µm) were able to remove the dissolved MC-LR. The originally small-sized cells grew during incubation, as shown by transmission electron microscopy, and changed in both cell size and morphology. The analysis of 16S rDNA sequences revealed that communities originated from < 0.22 and < 0.45 µm fractions diverged in taxonomic composition although they shared certain bacterial taxa. The presence of MC-LR shifted the structure of < 0.45 µm communities in comparison to those maintained without toxin. Actinobacteria was initially dominant and after incubation with MC-LR Proteobacteria predominated. There was a clear enhancement of taxa already known to degrade MC-LR such as Methylophilaceae. Small-sized bacteria constitute a diverse and underestimated fraction of microbial communities, which participate in the dynamics of MC-LR in natural environments.