Bloom Events Research Articles

Bio-optical properties of the cyanobacterium Nodularia spumigena

Abstract. In the last century, an increasing number of extreme weather events have been experienced across the globe. These events have also been linked to changes in water quality, especially due to heavy rains, flooding, or droughts. In terms of blue economic activities, harmful algal bloom events can pose a major threat, especially when they become widespread and last for several days. We present and discuss advanced measurements of a bloom dominated by the cyanobacterium Nodularia spumigena conducted by hyperspectral optical technologies via experiments of opportunity. Absorption coefficients, absorbance and fluorescence were measured in the laboratory, and these data are available at https://doi.org/10.4121/21610995.v1 (Wollschläger et al., 2022), https://doi.org/10.4121/21822051.v1 (Miranda et al., 2023) and https://doi.org/10.4121/21904632.v1 (Miranda and Garaba, 2023). Data used to derive the above-water reflectance are available from https://doi.org/10.4121/21814977.v1 (Garaba, 2023) and https://doi.org/10.4121/21814773.v1 (Garaba and Albinus, 2023). Additionally, hyperspectral fluorescence measurements of the dissolved compounds in the water were carried out. These hyperspectral measurements were conducted over a wide spectrum (200–2500 nm). Diagnostic optical features were determined using robust statistical techniques. Water clarity was inferred from Secchi disc measurements (https://doi.org/10.1594/PANGAEA.951239, Garaba and Albinus, 2022). Identification of the cyanobacterium was completed via visual analysis under a microscope. Full sequences of the 16S rRNA and rbcL genes were obtained, revealing a very strong match to N. spumigena; these data are available via GenBank: https://www.ncbi.nlm.nih.gov/nuccore/OP918142/ (Garaba and Bonthond, 2022b) and https://www.ncbi.nlm.nih.gov/nuccore/OP925098 (Garaba and Bonthond, 2022a). The chlorophyll-a and phycocyanin levels determined are available from https://doi.org/10.4121/21792665.v1 (Rohde et al., 2023). Our experiments of opportunity echo the importance of sustainable, simplified, coordinated and continuous water quality monitoring as a way to thrive with respect to the targets set in the United Nations Sustainable Development Goals (e.g. 6, 11, 12 and 14) or the European Union Framework Directives (e.g. the Water Framework Directive and Marine Strategy Framework Directive).

Lethal and sublethal effects towards zebrafish larvae of microcystins and other cyanopeptides produced by cyanobacteria

Cyanobacterial blooms affect aquatic ecosystems across the globe and one major concern relates to their toxins such as microcystins (MC). Yet, the ecotoxicological risks, particularly non-lethal effects, associated with other co-produced secondary metabolites remain mostly unknown. Here, we assessed survival, morphological alterations, swimming behaviour and cardiovascular functions of zebrafish (Danio rerio) upon exposure to cyanobacterial extracts of two Brazilian Microcystis strains. We verified that only MIRS-04 produced MCs and identified other co-produced cyanopeptides also for the MC non-producer NPCD-01 by LC-HRMS/MS analysis. Both cyanobacterial extracts, from the MC-producer and non-producer, caused acute toxicity in zebrafish with LC50 values of 0.49 and 0.98 mgdw_biomass/mL, respectively. After exposure to MC-producer extract, additional decreased locomotor activity was observed. The cyanopeptolin (micropeptin K139) contributed 52% of the overall mortality and caused oedemas of the pericardial region. Oedemas of the pericardial area and prevented hatching were also observed upon exposure to the fraction with high abundance of a microginin (Nostoginin BN741) in the extract of the MC non-producer. Our results further add to the yet sparse understanding of lethal and sublethal effects caused by cyanobacterial metabolites other than MCs and the need to better understand the underlying mechanisms of the toxicity. We emphasize the importance of considering mixture toxicity of co-produced metabolites in the ecotoxicological risk assessment of cyanobacterial bloom events, given the importance for predicting adverse outcomes in fish and other organisms.

Sub-tropical benthic/epiphytic dinoflagellates of Aotearoa New Zealand and Rangitāhua Kermadec Islands

Temperatures and temperature anomalies have been increasing in the sub-tropical regions of Aotearoa New Zealand and these changes may impact on harmful algal bloom (HAB) events. Benthic and epiphytic dinoflagellates, particularly the toxin producers, are the focus of this study as it is predicted that under future climate conditions they may produce more toxins or marine animals may become more susceptible to them. The results of past expeditions to Rangitāhua Kermadec Islands and sampling trips to Northland, Aotearoa New Zealand, are summarised and the results of the most recent trips to both regions are presented. The macroalgal habitats of the dinoflagellates are also characterised. Dinoflagellate species not previously identified in Rangitāhua include Coolia canariensis, C. palmyrensis, and C. tropicalis, all identified by DNA sequencing of the large subunit ribosomal RNA region. Gambierdiscus polynesiensis was again isolated and produced 44-methylgambierone and gambierone, and one isolate produced ciguatoxins, the cause of Ciguatera Poisoning. An Ostreopsis tairoto isolate, as analysed by the oxidative cleavage method, produced a palytoxin (PLTX)-like amine oxidation fragment, but when analysed for PLTX-like analogues using a new intact method none were detected indicating an ‘unknown’ PLTX-like compound is produced by this isolate. Isolates of O. cf. siamensis (Ostreopsis sp. 9), collected in Northland, were also analysed using the oxidative cleavage method, with the common PLTX-like amine fragment and the amide fragment corresponding to bishomoPLTX detected in all isolates. Again, the intact method indicated no detections in the isolates, again suggesting an unknown compound was being produced by these isolates. Prorocentrum hoffmannianum isolates produced okadaic acid (OA) and isoDTX-1 and P. lima isolates produced OA, DTX-1, and isoDTX-1. It is expected that new species of potentially harmful, benthic dinoflagellates will continue to be recorded in Aotearoa New Zealand and the results from Rangitāhua provide a guide to the HAB species to expect in sub-tropical Northland as the oceans continue to warm.

Effects of the harmful alga Margalefidinium (aka Cochlodinium) polykrikoides on clearance rates of the hard clam, Mercenaria mercenaria

Harmful algal blooms (HABs) such as those formed by the ichthyotoxic dinoflagellate, Margalefidinium (aka Cochlodinium) polykrikoides can have adverse effects on bivalves. While M. polykrikoides has caused significant die offs of bivalves and other marine organisms, the Northern quahog or hard clam, Mercenaria mercenaria, is comparatively more resistant to this HAB. This study quantified clearance rates of juvenile hard clams (10-20 mm) exposed to three different North American populations of M. polykrikoides (bloom, strain CP1, strain CPSB-1G) as well as the nonharmful cryptophyte, Rhodomonas salina and the nonharmful dinoflagellate, Gymnodinium aureolum, in single and mixed algal exposures. Multiple biovolume exposures with M. polykrikoides bloom water and R. salina (1,000, 1,500, 3,000 cells mL-1M. polykrikoides biovolume equivalent) were completed to assess the effects of increasing biomass on hard clam clearance rates and selection. Hard clams opened and actively cleared algal mixtures at and below 1,000 M. polykrikoides cells mL-1. During single species exposures, strain CPSB-1G and R. salina were cleared significantly faster than wild M. polykrikoides populations and strain CP1. During mixed exposures, R. salina was cleared significantly faster than CPSB-1G but not other M. polykrikoides populations and there was no difference between hard clam clearance rates of G. aureolum and R. salina. Clearance rates of M. polykrikoides at ≥1,500 cells mL-1M. polykrikoides/R. salina mixtures were not significantly different than zero unlike clearance of those at <1,000 cells mL-1 indicating a density dependent effect of blooms. Collectively, the results demonstrate that hard clams can actively clear M. polykrikoides cells at moderate (≤1,000 cells mL-1) but not elevated (> 1,000 cells mL-1) bloom densities. Given this, and the documented survival of hard clams during blooms, M. mercenaria may be candidate for aquaculture and restoration in regions prone to HABs caused by M. polykrikoides.

Automatic area estimation of algal blooms in water bodies from UAV images using texture analysis

Algal blooms, the spread of algae on the surface of water bodies, have adverse effects not only on aquatic ecosystems but also on human life. The adverse effects of harmful algal blooms (HABs) necessitate a convenient solution for detection and monitoring. Unmanned aerial vehicles (UAVs) have recently emerged as a tool for algal bloom detection, efficiently providing on-demand images at high spatiotemporal resolutions. This study developed an image processing method for algal bloom area estimation from the aerial images (obtained from the internet) captured using UAVs. As a remote sensing method of HAB detection, analysis, and monitoring, a combination of histogram and texture analyses was used to efficiently estimate the area of HABs. Statistical features like entropy (using the Kullback–Leibler method) were emphasized with the aid of a gray-level co-occurrence matrix. The results showed that the orthogonal images demonstrated fewer errors, and the morphological filter best detected algal blooms in real time, with a precision of 80%. This study provided efficient image processing approaches using on-board UAVs for HAB monitoring.

Exploring a multi-objective optimization operation model of water projects for boosting synergies and water quality improvement in big river systems

Due to excessive nutrient enrichment and rapidly increasing water demand, the occurrence of riverine environment deterioration events such as algal blooms in rivers of China has become more frequent and severe since the 1990s, which has imposed harmful consequences on riverine ecosystems. However, tackling river algal blooms as an important issue of restoring riverine environment is very challenging because the complex interaction mechanisms between the causes are impacted by multiple factors. The contributions of our study consist of: (1) optimizing joint operation of water projects for boosting synergies of water quality and quantity, and hydroelectricity; and (2) preventing algal bloom from perspectives of hydrological and water-quality conditions by regulating water releases of water projects. This study proposed a multi-objective optimization methodology grounded on the Non-dominated Sorting Genetic Algorithm to simultaneously minimize the excess values of algal bloom indicators (water quality, O1), minimize the used reservoir capacity for water supply (water quantity, O2), and maximize the hydropower generation (hydroelectricity, O3). The proposed methodology was applied to several catastrophic algal bloom events that took place between 2017 and 2021 and thirteen water projects in the Hanjiang River of China. The results indicated that the proposed methodology largely stimulated the synergistic benefits of the three objectives by reaching a 36.7% reduction in total nitrogen and phosphorus concentrations, a 33.1% improvement in the remaining reservoir capacity, and a 41.0% improvement in hydropower output, as compared with those of the standard operation policy (SOP). In addition, the optimal water release schemes of water projects would increase the minimum streamflow velocity of downstream algal bloom control stations by 8.6%–9.4%. This study provides a new perspective on water project operation in the environmental improvement in big river systems while boosting multi-objectives synergies to support environmentalists and decision-makers with scientific guidance on sustainable water resources management.

Fish Productivity Response to Water Quality Variations: A Case Study of Nyumba ya Mungu Dam, in Pangani Water Basin, Tanzania

Fish habitat degradation, such as water pollution due to the rapid expansion of incompatible land uses, is one of the noteworthy challenges to freshwater ecosystems. Elevated contents of nutrients and contaminants in water are some of the imperative challenges. This research was conducted to investigate the link between water qualities and fish productivity in the Nyumba ya Mungu Dam, whose fishery potential had decreased by 95% between 1972 and 2018. Physicοchemical characteristics, namely, temperature, pH, dissolved oxygen (DO), turbidity, total nitrogen, total phosphorus, chlorophyll a, and the water depth of fishing net location, were assessed following standard procedure. Fish catches per unit effort representing fish biomass/productivity were monitored for twelve months from January to December 2019. Pearson’s correlation analysis indicated that fish catch per unit effort was positively and significantly correlated with turbidity (r = 0.461, P < 0.01) and TP (r = 0.405, P < 0.01). Stepwise multiple regression model results indicated that turbidity, dissolved oxygen, and the depth of the fishing net location are the statistically significant predictors of fish catch per unit effort which represented fish biomass. Findings further indicated that the model combining turbidity and dissolved oxygen predicted a 24% change in fish catch per unit effort, whereas turbidity, dissolved oxygen, and the depth of fishing net location contributed a 28.9% change in fish catch per unit effort. In conclusion, fish productivity in the NMD is limited by organic matter availability and nutrient levels that cause algae bloom occurrence. Turbidity is an indicator of organic matter availability and the effect of algae bloom on fish productivity. Inflow of nutrients to the dam nourishes the algae biomass, thus creating vicious cycles on fish productivity as fish species in the dam failed to take advantage of high primary production by algae.

Impact of climate risk materialization and ecological deterioration on house prices in Mar Menor, Spain

The frequency and severity of extreme events related to climate change have intensified worldwide in the last decades. It is documented that increasing extreme rainfall and flooding cause more nutrient runoff into waterbodies, initiating numerous harmful algal bloom (HAB) events, especially in fragile ecosystems. We analyze the dramatic economic damage of one of these episodes in Mar Menor, the largest salt-water lagoon in Europe. We show that when the public perceived the severity of environmental degradation, the return on housing investment was 43% lower in the surroundings than in similar neighboring zones 6 years after the HAB (2015). This represents a loss in housing wealth of more than 4000 million euros, around ten times the gains of changing from dry-farming to irrigated crops, which makes this ecosystem fragile. Hence, we quantify some of the economic consequences of ecological deterioration linked to episodes of Global Climate Change.

High-precision calculation and experiments on the thermal blooming of high-energy lasers.

Thermal blooming (TB) is one of the important factors affecting the quality of high-energy laser beams. Reasonable simulation of thermal blooming is important to the application of a high-energy laser. However, reported investigations on TB simulation are mainly based on one method, such as the perturbation method or the phase screen method, which often leads to obvious errors in some conditions. In the paper, the reasonable ranges of optical generalized distortion parameters for both methods are determined based on the reported experimental data, which solves the problem of accurate TB simulations for the first time. In addition, the dynamic effect of thermal blooming is also calculated. Finally, the formula method is presented to extract the phase of thermal blooming distortion. We then use LC-SLM (Liquid crystal spatial light modulator) to emulate thermal blooming effect in the lab. The experimental results are more consistent with the numerical simulation results than conventional phase extraction methods. Our work provides a quantitatively and programmable way to accurately simulate TB with LC-SLM in the lab.

Complex interactions among temperature, microplastics and cyanobacteria may facilitate cyanobacteria proliferation and microplastic deposition

Cyanobacterial blooms are a global concern prone to causing environmental and economic damages and are tightly linked to anthropogenic nutrient inputs. Likewise, microplastic pollution has also become globally ubiquitous inevitably co-occurring with blooms. However, little is known on how microplastics influence cyanobacterial physiologically and how potential physiological changes can affect their buoyancy, ultimately impacting their fate, and transport, including deposition during bloom events. Interactions of environmental relevant concentrations of high-density polyethylene microplastics (MPs) (0–0.4 mg/mL) and temperatures (2.5–32.5 °C) were evaluated to assess the effects of MPs on interactions of cyanobacteria Anabaena variabilis’s growth, total organic carbon concentrations, extracellular polymeric substances (EPS) production, and MP deposition. Microplastics both stimulated and inhibited A. variabilis growth depending on the concentration. Lower MPs concentrations (0.1–0.2 mg/L) increased A. variabilis growth while higher MP concentrations (>0.3 mg/mL) impeded it across all temperatures studied. Carbon sources leached from MPs may have been a contributing factor to the increased growth at lower MPs concentration, while higher MPs concentration potentially shaded A. variabilis inhibiting its growth. Shading may have induced stress which corresponded with an observed increase in EPS production by A. variabilis when exposed to MP. Extracellular polymeric substances generation activated under adverse circumstances (MPs 0.4 mg/mL) enhanced MP deposition. Overall, our findings indicate that MPs play an important role in cyanobacterial blooms, and that these blooms may enhance MPs deposition.

Hydantoanabaenopeptins from Lake Kinneret Microcystis Bloom, Isolation, and Structure Elucidation of the Possible Intermediates in the Anabaenopeptins Biosynthesis.

Anabaenopeptins are common metabolites of cyanobacteria. In the course of reisolation of the known aeruginosins KT608A and KT608B for bioassay studies, we noticed the presence of some unknown anabaenopeptins in the extract of a Microcystis cell mass collected during the 2016 spring bloom event in Lake Kinneret, Israel. The 1H NMR spectra of some of these compounds presented a significant difference in the appearance of the ureido bridge protons, and their molecular masses did not match any one of the 152 known anabaenopeptins. Analyses of the 1D and 2D NMR, HRMS, and MS/MS spectra of the new compounds revealed their structures as the hydantoin derivatives of anabaenopeptins A, B, F, and 1[Dht]-anabaenopeptin A and oscillamide Y (1, 2, 3, 6, and 4, respectively) and a new anabaenopeptin, 1[Dht]-anabaenopeptin A (5). The known anabaenopeptins A, B, and F and oscillamide Y (7, 8, 9, and 10, respectively) were present in the extract as well. We propose that 1-4 and 6 are the possible missing intermediates in the previously proposed partial biosynthesis route to the anabaenopeptins. Compounds 1-6 were tested for inhibition of the serine proteases trypsin and chymotrypsin and found inactive at a final concentration of ca. 54 μM.

Incidence of harmful algal blooms in pristine subtropical ocean: a satellite remote sensing approach (Jeju Island)

Despite the increasing numbers of red tide events in the pristine subtropical ocean, a paucity of previous observations has limited understanding of harmful algae in the seas around the Korean Peninsula. Therefore, using six years (2012–2017) of Geostationary Ocean Color Imager (GOCI) satellite data, we characterized the red tides around Jeju Island, a volcanic island located near the paths of the Jeju Warm Current and Tsushima Warm Current, using the Normalized Red Tide Index (NRTI) method. The seawater around Jeju Island has for a long time been considered to be very clear, with relatively low suspended particulate matter concentrations and few harmful algae. Nonetheless, the satellite-based NRTI detection method used in this study detected and supported the existence of red tides in the coastal region around Jeju Island. Analysis of the red tide distribution showed that red tide first began to appear near the western coast of Jeju Island, then developed in the northern and eastern coastal regions, and finally vanished in the eastern coastal region. The monthly averages of the NRTI demonstrated a bloom event from April to May in every year. Additional fall blooms were detected in August–September, particularly in 2013 and 2016. The NRTI revealed strong interannual variations. The longest blooms occurred in 2015, and the most comprehensive and strongest event occurred in the spring of 2016. The latter three years (2015–2017) had much higher NRTI than the former three years (2012–2014). The probability of red tide occurrence at a given point during the 6-year study period revealed spatial differences. Relatively high probability of 0.3–0.5 was determined along the northern coastal region, whereas low probability of less than 0.2 was found along the southern region. Ground truth data also showed more frequent observations and higher red tide cell densities along the northern coast. Changes in NRTI in spring are positively correlated with changes in ENSO indices in winter. This study is the first to use a satellite-based approach with a vast long-term satellite database to elucidate the existence and probability of red tides near Jeju Island. We anticipate that this study will provide a useful strategy for remote monitoring of harmful algal blooms over wide regions using optical data.

Detection of secondary cyanobacterial metabolites using LC-HRMS in Lake Karaoun

Harmful algal blooms events have been reported worldwide and during the last decades are occurred with increasing frequency and intensity due to the climate change and the high inputs of nutrients in freshwaters from anthropogenic activities. During blooms cyanobacteria release in water their toxic secondary metabolites, known as cyanotoxins, along with other bioactive metabolites. Due to the negative impacts of these compounds on aquatic ecosystems and public health, there is an urgent need to detect and identify known and unknown cyanobacterial metabolites in surface waters. In the frame of the present study, a method based on liquid chromatography - high resolution mass spectrometry (LC-HRMS) was developed to investigate the presence of cyanometabolites in bloom samples from Lake Karaoun, Lebanon. Data analysis was performed using Compound Discoverer software with related tools and databases in combination to the CyanoMetDB mass list for detection, identification and structural elucidation of the cyanobacterial metabolites. In the course of this study, 92 cyanometabolites were annotated including 51 cyanotoxins belonging to microcystins, 15 microginins, 10 aeruginosins, 6 cyclamides, 5 anabaenopeptins, a cyanopeptolin, the dipeptides radiosumin B and dehydroradiosumin, the planktoncyclin and a mycosporine–like amino acid. Out of them, 7 new cyanobacterial metabolites, the chlorinated MC-ClYR, [epoxyAdda5]MC-YR, MC-LI, aeruginosin 638, aeruginosin 588, microginin 755C and microginin 727 were discovered. Moreover, the presence of anthropogenic contaminants was recorded indicating the pollution of the lake and emphasizing the need for assessment of the co-occurrence of cyanotoxins, other cyanobacterial metabolites and other compounds hazardous to the environment. Overall, results prove the suitability of the proposed approach for the detection of cyanobacterial metabolites in environmental samples but also highlight the necessity of spectral libraries for these compounds, considering the absence of their reference standards.

Disruption of fish gut microbiota composition and holobiont’s metabolome during a simulated Microcystis aeruginosa (Cyanobacteria) bloom

BackgroundCyanobacterial blooms are one of the most common stressors encountered by metazoans living in freshwater lentic systems such as lakes and ponds. Blooms reportedly impair fish health, notably through oxygen depletion and production of bioactive compounds including cyanotoxins. However, in the times of the “microbiome revolution”, it is surprising that so little is still known regarding the influence of blooms on fish microbiota. In this study, an experimental approach is used to demonstrate that blooms affect fish microbiome composition and functions, as well as the metabolome of holobionts. To this end, the model teleost Oryzias latipes is exposed to simulated Microcystis aeruginosa blooms of various intensities in a microcosm setting, and the response of bacterial gut communities is evaluated in terms of composition and metabolome profiling. Metagenome-encoded functions are compared after 28 days between control individuals and those exposed to highest bloom level.ResultsThe gut bacterial community of O. latipes exhibits marked responses to the presence of M. aeruginosa blooms in a dose-dependent manner. Notably, abundant gut-associated Firmicutes almost disappear, while potential opportunists increase. The holobiont’s gut metabolome displays major changes, while functions encoded in the metagenome of bacterial partners are more marginally affected. Bacterial communities tend to return to original composition after the end of the bloom and remain sensitive in case of a second bloom, reflecting a highly reactive gut community.ConclusionGut-associated bacterial communities and holobiont functioning are affected by both short and long exposure to M. aeruginosa, and show evidence of post-bloom resilience. These findings point to the significance of bloom events to fish health and fitness, including survival and reproduction, through microbiome-related effects. In the context of increasingly frequent and intense blooms worldwide, potential outcomes relevant to conservation biology as well as aquaculture warrant further investigation.1eB3aaX_ggiGqr9dWKj2NwVideo

Cultivable seaweeds eliminate the lethal effects of the harmful alga, Margalefidinium polykrikoides, on early life stage fish

Margalefidinium polykrikoides (aka Cochlodinium polykrikoides) is a harmful algal bloom (HAB)-forming dinoflagellate that is well-known for its ichthyotoxic properties, causing economically significant fish kills globally during bloom events. In this study, we evaluate the ability of seaweeds, including Ulva spp., Gracilaria sp., Chondrus crispus, and Grateloupia turuturu to mitigate the ichthyotoxicity of cultured and bloom populations of M. polykrikoides towards early life stage forage fish (Menidia menidia, Menidia beryllina, and Cyprinodon variegatus). In assays with both cultured and wild M. polykrikoides, live seaweed thalli – particularly Ulva spp. – significantly extended fish survival in all cases, with higher concentrations of seaweed resulting in a greater protective effect. In some cases, seaweeds completely mitigated fish mortality, resulting in survival not statistically different from the control. DMSP, an antioxidant compound produced by seaweeds, significantly reduced the ichthyotoxic effects of M. polykrikoides (p < 0.005) with no Ulva present, suggesting that the antioxidant properties of seaweeds and seaweed metabolites may be partly responsible for the protective effects. Partition chamber survival assays demonstrated that close physical proximity between the fish and Ulva was necessary for a protective effect to occur. Finally, we show that over longer timescales, very low concentrations of Ulva (0.2 g L-1) can significantly reduce (68–92% reduction) bloom populations of wild M. polykrikoides compared to control (p < 0.05). Collectively, the results of this study demonstrate that (1) aquaculture of Ulva spp. may be a viable strategy to protect caged fish farms from M. polykrikoides blooms, (2) existing beds of Ulva and other seaweeds may provide a refuge for vulnerable fish populations during M. polykrikoides blooms, and (3) the protective effects of seaweeds from M. polykrikoides ichthyotoxicity is due to a localized antioxidant-rich microenvironment around the surface of the seaweed, neutralizing short-lived reactive oxygen species produced by M. polykrikoides.

Nonlinear response of Equatorial Western Pacific phytoplankton blooms to ‘double-dip’ La Niña events

Phytoplankton in the equatorial western Pacific tends to bloom during consecutive (‘double-dip’) La Niña events with nonlinear characteristics: extremely high chlorophyll-a (Chl-a) concentrations typically occur during the second-year La Niña events even when the associated SST anomalies are significantly weakened. Photosynthetically available radiation is found to have the strongest correlation with the equatorial western Pacific Chl-a fluctuations. However, barrier layer variation is critical in driving the strong bloom events seen in the second-year La Niña, which can be further explained by the nonlinear heat advection within the isothermal layer. To improve the current climate models’ performance in simulating the western Pacific phytoplankton bloom events, it is recommended that the influence of barrier layer should be better considered.

Source characterization of dissolved organic matter in the eastern Beagle Channel from a spring situation

Dissolved organic matter (DOM) was analyzed by its optical and fluorescent properties in order to study its distribution, source and transformation in relation to microbial abundances, chlorophyll and physicochemical gradients along a transect in the eastern Beagle Channel (BC) during austral spring 2019. Moreover, DOM evolution was followed during three tidal cycles in two fixed stations (F1, F2) separated by the Mackinlay Strait, a hydrographic frontier between water masses under stronger continental influence (inner sector) and that of less modified Sub-Antarctic waters (outer sector). The fluorescence signals of protein- and humic-like compounds were used as a proxy for labile and non-labile material, respectively, while the concentration of nano-, pico- and virioplankton populations, chlorophyll-a (Chl-a) and dissolved organic carbon (DOC) were used as a proxy for biological activity. Moreover, several spectroscopic indices, such as the indicator of microbially produced DOM (BIX), the Freshness index (FIX), an indicator of molecular weight, the Slope Ratio (SR) and an indicator of chromophoric DOM (CDOM), were used to trace the quality and origin of DOM. Chl-a concentration was generally low in the sampling area (< 1 μg L−1) but increased towards the end of the campaign and especially during the visit of F1 along with the concentration of picoeukaryotes and the protein-like fluorophores evidencing the onset of a bloom event. Protein-like fluorophores peaked in the euphotic zone of the inner sector of the BC while humic-like material of terrestrial origin was homogeneously distributed throughout the water column and showed a decreasing gradient towards the outer sector and Atlantic waters. Furthermore, the inner sector was characterized by higher amounts of CDOM, high molecular weight material and more recalcitrant DOM. Accumulation of autochthonous humic-like material in bottom waters of the inner sector along with enhanced values of FIX and BIX preceded by colored organic material suggest an efficient functioning of the microbial carbon pump fueled by terrestrial DOM sources in these waters.

Physical Drivers of Monthly Variation in Phytoplankton Community in the Tidal Freshwater Zone of the Macrotidal Qiantang River Estuary, Eastern China: Implications for Reducing the Risk of Harmful Cyanobacterial Blooms

AbstractThe Qiantang river estuary flows into Hangzhou Bay, on the East China Sea, and has one of the largest tidal bores worldwide. The tidal freshwater zone (TFZ) in this shallow macrotidal estuary is subjected to strong riverine and marine forcings. We investigated monthly variation of phytoplankton and environmental drivers in the upper and lower sections of TFZ during 2016. Large numbers of phytoplankton taxa (422) and genera (161) were identified. Diatoms were dominant in most months, but cyanobacteria abundance reached its greatest in warm months when runoff was low. Surprisingly, relatively high dominances of marine diatom species (e.g., Cyclotella stylorum, Skeletonema, and Thalassiosira) were observed in the TFZ with salinities usually &lt;1 PSU. Microcystis contributed up to 50% to phytoplankton abundance in the upper TFZ in September, consistent with upstream bloom events. Abundances of phytoplankton and cyanobacteria were significantly negatively correlated with monthly runoff and sediment fluxes. Generalized additive models suggested that variation in phytoplankton abundance was largely explained by river flow, temperature and nutrients. Phytoplankton community composition varied significantly across different months and sections. Redundancy analysis indicated that temperature and flow rate explained more variation in phytoplankton community than other variables, but nutrients, Secchi depth and salinity also contributed significantly to the explained variation. Variance partitioning analysis confirmed that phytoplankton variation was largely regulated by physical variables rather than nutrients. These findings highlight the unexpectedly great phytoplankton species richness, dominance of marine diatoms, and physical drivers in the eutrophic macrotidal TFZ under strong tidal forcing.

Do Late Bloomers Exist Among Adjudicated Youth?: Examining Parental Factors and ADHD Symptomatology as Contributors to Protective Bud and Bloom Effects

Do Late Bloomers Exist Among Adjudicated Youth?: Examining Parental Factors and ADHD Symptomatology as Contributors to Protective Bud and Bloom Effects

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.