Development Of Harmful Algal Blooms Research Articles

Sensitivity analysis of a hydrodynamic and harmful algal model in a riverine system

Simulating algae blooms using a hydrodynamic-water quality model is challenging because it requires a thorough understanding of physical and biological processes and involves numerous parameters. This study conducted a sensitivity analysis of the EFDC+ hydrodynamic and water quality model for simulating cyanobacteria growth, an important Harmful Algal Bloom (HAB) species in the Ohio River, USA. The sensitivity analysis assessed 23 model input parameters, divided into nine functional groups according to their characteristics. This assessment analyzes the impact of changing these input parameters on four water quality model outputs including algae (i.e., cyanobacteria), dissolved oxygen, total nitrogen, and total phosphorus. Light extinction parameters, maximum algal growth rate, and algal base metabolism were identified as the most sensitive parameters for simulating algal growth. Solar radiation required for algal growth was moderately sensitive. Currently, there are only a few studies that simulate HAB dynamics in riverine systems. This study deepens our understanding of HAB development in rivers with lock and dam structures that create a series of pools along the river. Future work will involve focusing on the sensitive parameters in model calibration.

Multi-year three-dimensional simulation of seasonal variation in phytoplankton species composition in a large shallow lake

Lake Erie has been negatively impacted by multiple stressors, including nutrient enrichment and climate change, that have exacerbated eutrophication and harmful algal blooms. Management of these long-term water quality problems requires numerical models that can be run over years to decades. The three-dimensional hydrodynamics and biogeochemistry models applied to date, however, have not been tested for continuous runs longer than one year and have not been shown to accurately reproduce seasonal variation in phytoplankton species composition (e.g., the development of harmful algal blooms) over decadal timescales. We simulated the three-dimensional nutrient and phytoplankton concentrations in western Lake Erie continuously from 2002 to 2014. Using a single parameter set, we were able to reproduce both seasonal and inter-annual variation in phytoplankton species composition. The model qualitatively reproduced the observed seasonal succession (i.e., variation in phytoplankton species composition), including the spring diatom bloom and late summer cyanobacterial growth. This study demonstrates that three-dimensional models can be applied for multi-year simulations of nutrients and phytoplankton to inform large lake research and management.

Response of the toxic dinoflagellate Alexandrium minutum to exudates of the eelgrass Zostera marina

Biotic interactions are a key factor in the development of harmful algal blooms. Recently, a lower abundance of planktonic dinoflagellates has been reported in areas dominated by seagrass beds, suggesting a negative interaction between both groups of organisms. The interaction between planktonic dinoflagellates and marine phanerogams, as well as the way in which bacteria can affect this interaction, was studied in two experiments using a non-axenic culture of the toxic dinoflagellate Alexandrium minutum exposed to increasing additions of eelgrass (Zostera marina) exudates from old and young leaves and to the presence or absence of antibiotics. In these experiments, A. minutum abundance, growth rate and photosynthetic efficiency (Fv/Fm), as well as bacterial abundance, were measured every 48 h. Toxin concentration per cell was determined at the end of both experiments. Our results demonstrated that Z. marina exudates reduced A. minutum growth rate and, in one of the experiments, also the photosynthetic efficiency. These results are not an indirect effect mediated by the bacteria in the culture, although their growth modify the magnitude of the negative impact on the dinoflagellate growth rate. No clear pattern was observed in the variation of toxin production with the treatments.

Predicting Chlorophyll-a Concentration and Harmful Algal Blooms in Lake Okeechobee Using Time-Series MODIS Satellite Imagery and Long Short-Term Memory

Highlights A 10-year dataset of time-series MODIS imagery and in situ Chl-a concentration were curated for Lake Okeechobee. LSTM significantly outperformed KNN, SVR, and RF for Chl-a prediction and subsequent HAB detection. The optimal window length was found to be 13 days with a 4-day temporal resolution for the LSTM model. KNN, SVR, and RF models were not effective at utilizing the temporal dynamics of the input features. Abstract. Harmful algal blooms (HABs) in inland waterbodies are a global concern due to their negative impact on human, animal, and ecosystem health. Chlorophyll-a (Chl-a) concentration is an important water quality parameter for monitoring HABs. While statistical and machine learning (ML) models have been widely studied to predict Chl-a concentration and HABs based on single-time-point satellite data, this work assessed whether long short-term memory (LSTM) can improve both tasks by leveraging temporal features in time-series MODIS satellite images compared to three classical ML models, including k-nearest neighbor (KNN), support vector regression (SVR), and random forest (RF). A dataset of daily MODIS images and monthly in situ Chl-a concentration measurements from 2011 to 2020 was curated for Lake Okeechobee, Florida. A window size of 13 days with a temporal resolution of four days was found to produce the optimal performance for LSTM, which significantly outperformed KNN, SVR, and RF for Chl-a prediction with a root mean square error of 11.95 µg/L, a mean absolute error of 8.55 µg/L, and a R2 value of 0.43. The superior performance of LSTM for Chl-a prediction was likely due to its ability to leverage the temporal dynamics in the features associated with HAB development. The Chl-a predictions were further used to determine HAB events, showing better accuracy and a significantly higher F1 score for LSTM over the other models. The study suggested that combining LSTM with high-temporal-resolution time-series data should be preferred over applying common ML models on time-series or single-time-point remote sensing data for Chl-a and HAB monitoring. Keywords: Cyanobacteria, LSTM, Machine Learning, Remote Sensing, Water Quality.

The land-sea breeze influences the oceanography of the southern Benguela upwelling system at multiple time-scales

The physical and biogeochemical functioning of eastern boundary upwelling systems is generally understood within the context of the upwelling - relaxation cycle, driven by sub-diurnal wind variability (i.e. with a time-scale of greater than a day). Here, we employ a realistically configured and validated 3D model of the southern Benguela upwelling system to quantify the impact of super-diurnal winds associated with the land-sea breeze (LSB). The ocean response to the LSB is found to be particularly enhanced within St Helena Bay (SHB), a hotspot for productivity which is also prone to Harmful Algal Bloom (HAB) development. We attribute the enhanced response to a combination of near-critical latitude for diurnal-inertial resonance (~32.5°S), the local enhancement of the LSB, and the local development of a shallow stratified surface layer through bay retention. Pronounced advection of the surface layer by diurnal-inertial oscillations contributes to large differences in day- and night-time sea surface temperatures (SST’s) (more than 2°C on average in SHB). Event-scale diapycnal mixing is particularly enhanced within SHB, as highlighted by a numerical experiment initialised with a subsurface passive tracer. These super-diurnal processes are shown to influence sub-diurnal dynamics within SHB through their modulation of the vertical water column structure. A deeper thermocline retains the upwelling front closer to land during active upwelling, while geostrophically-driven alongshore flow is impacted through the modulation of cross-shore pressure gradients. The results suggest that the LSB is likely to play an important role in the productivity and therefore HAB development within SHB, and highlight potential challenges for observational systems and models aiming to improve our understanding of the physical and biological functioning of the system.

Environmental Parameters And Phytoplankton Community Quality: Implications For Food Safety In Coastal Communities

This study aimed to evaluate environmental parameters and phytoplankton quality as well as the implications for the food safety of seafood-consuming coastal communities. The study was conducted in coastal waters of South Sulawesi, Indonesia at four sites (three stations/site): Pangkep (PK), Kuri (KR), Maros (MR), and Tallo (TL) during June, August, and October 2020. Observations formed three spatial clusters: MR1, PK; MR2, MR3, TL; KR (92.5 % similarity), and two temporal clusters: June 2020; August and October 2020 (87.9 % similarity). PCA showed parameters most strongly characterizing TL, KR, and MR (except MR1) were high levels of salinity, nitrate, nitrite, ammonium, silicate, temperature, pH, and abundance of both phytoplankton that can form harmful algal blooms (HABs) and non-HAB forming phytoplankton (non-HABs), with low current velocity. PK was characterized by high current velocity, non-HABs, orthophosphate, ammonium, nitrite, and turbidity with low nitrate and HABs. Main characterizing parameters in the temporal PCA were high current velocity and HABs with low orthophosphate in June 2020; high nitrate, ammonium, orthophosphate, and non-HABs with even lower HABs in August 2020; high turbidity, temperature, and salinity with low pH, nitrite, silicate, and HABs in October 2020. Current velocity (low at TL, KR, MR and high at PK) influenced both non-HABs and HABs. The results indicate that faster currents may have impeded HABs development so that the phytoplankton quality was still good. Therefore, the fish from these waters can be considered safe for human consumption, thereby contributing to maintaining the health of coastal communities.

Competitive advantages of HAB species under changing environmental conditions in the coastal waters of the Bohai Sea, Yellow Sea and East China Sea

Harmful algal blooms (HABs) have become a severe ecological problem in coastal waters in recent decades. Under the enhanced anthropogenic disturbance, the Eastern Chinese coastal seas (ECCS), including the coastal waters of the Bohai Sea (BS), Yellow Sea and East China Sea, have been suffering environmental changes dramatically during the past 40 years. However, it is not clear how changes in coastal nutrient pollution, hydrodynamics and climate promote the succession of dominant HAB species simultaneously. In this study we used physical criteria (light availability, temperature and salinity) and chemical criteria (strategy of nutrient utilization) to quantify the competitiveness of the primary HAB species in the ECCS, i.e. Skeletonema costatum, Noctiluca scintillans, Prorocentrum donghaiense, Karenia mikimotoi, and Aureococcus anophagefferens. A risk assessment module has been developed and applied to this study based on the physical criteria of the main HAB species. Model result indicated a strong reliability on locating the potential physical habitat of blooms dominated by specific species. Imbalanced nutrient stoichiometry plays a vital role in HAB species succession in the ECCS, especially potential limitation of dissolved inorganic phosphorus. Due to long water residence time, persistence of nutrient imbalance and organic nutrient accumulation induce frequent blooms of Aureococcus anophagefferens in the BS. Observations and experiments have limitations when describing combining processes that influence HAB development, and need to be complemented with advanced mechanistic models for describing the hydrodynamics and biogeochemistry to allow for hindcasting and forecasting HAB risk under changing environmental conditions.

Analytical population dynamics underlying harmful algal blooms triggered by prey avoidance

A modified version of the NPZD ecosystem model is used to analytically examine the effects of predation avoidance, a possible mechanism for triggering harmful algal blooms (HAB). To resolve HAB development caused by predation avoidance, an additional phytoplankton functional group is considered, one that has slower nutrient uptake and better predation avoidance characteristics than the non-harmful phytoplankton group used in traditional NPZD models. Because the two phytoplankton groups (one non-harmful and one HAB) compete for only one resource within the same system, steady state (equilibrium) conditions cannot occur without the presence of zooplankton; only the non-harmful phytoplankton group, which defeats the HAB group in the resource competition, can survive in the equilibrium. The presence of sufficient zooplankton effectively acts to replenish the nutrient pool by consuming the non-harmful phytoplankton. When this occurs, two equilibrium states are found: one with both phytoplankton groups coexisting, and one that only includes the HAB group. The condition required for equilibrium is that the total nitrogen within the system should be larger than a threshold determined by model coefficients. The threshold and feasibility of the equilibrium are sensitive to the relative HAB predation avoidance coefficient. If the coefficient is larger than the ratio of net growth rates between the HAB and non-harmful phytoplankton group, the threshold becomes infinite, and an equilibrium is not feasible. The time scale for the system to reach an equilibrium state that includes a HAB group is determined asymptotically. The dependence of a threshold condition as a controlling factor may explain the regime shift of dominant species causing HABs. The ecosystem model is fully implemented into the Regional Ocean Modeling System and applied to an idealized coastal embayment (with depths and geometry taken from San Francisco Bay) to show numerically the dominance of prey avoidance dynamics in a natural shallow water environment that includes advection and diffusion. The analytical results improve strategies for HAB modeling and provide guidance for setting model coefficients necessary to resolve a HAB event.

Hindcasting harmful algal bloom risk due to land-based nutrient pollution in the Eastern Chinese coastal seas

Harmful algal blooms (HABs) have been increasing in frequency, areal extent and duration due to the large increase in nutrient inputs from land-based sources to coastal seas, and cause significant economic losses. In this study, we used the “watershed-coast-continuum” concept to explore the effects of land-based nutrient pollution on HAB development in the Eastern Chinese coastal seas (ECCS). Results from the coupling of a watershed nutrient model and a coast hydrodynamic-biogeochemical model show that between the 1980s and 2000s, the risk of diatom blooms and dinoflagellate blooms increased by 158% and 127%, respectively. The spatial expansion of HAB risk caused by dinoflagellates is larger than that of diatoms. The simulated suitability of the habitat for bloom of Aureococcus anophagefferens, a pico-plankton of non-diatom or dinoflagellate, in the Bohai Sea is consistent with observations spatially and temporally. To halt further nutrient accumulation in the ECCS, reductions of dissolved inorganic nitrogen (DIN) (16%) and dissolved inorganic phosphorus (DIP) (33%) loading are required. To improve the situation of distorted DIN:DIP ratios, even larger reductions of DIN are required, especially in the Bohai Sea. Our approach is a feasible way to predict the risk of HABs under the pressure of increasing anthropogenic nutrient pollution in coastal waters.

Extreme harmful algal blooms, climate change, and potential risk of eutrophication in Patagonian fjords: Insights from an exceptional Heterosigma akashiwo fish-killing event

The Patagonian fjords have experienced intense harmful algal blooms (HABs) in the last decade, affecting important aquaculture areas in southern Chile. Climatic anomalies have recently triggered ‘super blooms’ of opportunistic toxic microalgal genera, especially due to persistent thermal stratification which likely provides an optimal niche for HABs development in fjord systems. In March-April 2021, an intense and widespread bloom of the raphidophyte Heterosigma akashiwo caused high salmon mortalities (>6,000 t) in the Comau fjord, Los Lagos Region. A climate variability analysis showed the effects of the positive phase of the Southern Annular Mode (SAM > 1.2 hPa) overcame those of La Niña (Niño3.4 = -0.9 °C) leading to an intense drought on the northern part of Patagonia with record low rainfall (the 2nd driest summer in the last 70 years) and increased water temperature. A regional satellite analysis revealed an extreme and persistent shallow Mixed Layer Depth (MLD) during summer periods since 2019 within the inland seas. In situ vertical fine-resolution measurements during the bloom event showed high cell abundances in the first 3 m of the water column (max. ∼ 70,000 cells mL−1), associated with warmer water temperature (∼15.5 – 17.5 °C), low salinity (∼25–30 psu), moderate to high dissolved oxygen (5 – 8.5 mg/L) and extremely high fluorescence signals in dense superficial cell aggregations (max. 74.9 µg/L). A 18S rRNA metabarcoding analysis formally confirmed the presence of H. akashiwo and its almost monospecific bloom development at the water surface. HPLC pigment analysis showed the carotenoid fucoxanthin in high proportion (48.8 %) compared to other photosynthetic pigments, becoming a potential pigment biomarker for early satellite H. akashiwo detection. Cell growth and cytotoxic in vitro experiments revealed high phenotypic plasticity of Chilean H. akashiwo against sudden changes in salinity. An RTgill-W1 gill cell assay revealed high cytotoxic activity (viability down to ∼ 50 – 30 % of controls) only at high cell abundances (>40,000H. akashiwo cells mL−1), which was in accordance with histological examination of moribund salmon that showed gill damage and circulatory disorders mainly due to long-term exposure to hypoxic conditions and not to potent cytotoxic effects. The Party-MOSA particles dispersion model revealed a high retention of water masses within the Comau fjord during the H. akashiwo outbreak, a scenario that may have boosted fish kills due to enhanced cells patchiness, ichthyotoxins persistence and hypoxic conditions. A historical dissolved inorganic nutrient data analysis showed that inner Patagonian fjords maintain low N and P concentrations including those environments considered of high eutrophication risk. Low N:P (<16:1) ratios measured at Comau fjord during the 2021 suggests that toxic flagellates growth could be favored over diatoms; however, low N:Si (<1:1 – N deficiency) evidences a clear need for better understanding of the role of mixotrophy in the persistence of the 2021H. akashiwo bloom for several weeks. These results highlight the fact that HABs responses against climate drivers and potential eutrophication are not universal and need to be assessed yearly and locally, particularly because extreme droughts and intensive aquaculture in northern Patagonia are expected to continue throughout the 21st century.

Comparative Analysis of Bacillariophyceae Chloroplast Genomes Uncovers Extensive Genome Rearrangements Associated with Speciation.

The Bacillariophyceae is a species-rich, ecologically significant class of Bacillariophyta. Despite their critical importance in marine ecosystems as primary producers and in the development of harmful algal blooms (HABs), taxonomic research on Bacillariophyceae species has been hindered because of their limited morphological features, plasticity of morphologies, and the low resolution of common molecular markers. Hence molecular markers with improved resolution are urgently needed. Organelle genomes, which can be constructed efficiently with the recent development of high throughput DNA sequencing technologies and the advancement of bioinformatics tools, have been proposed as super barcodes for their higher resolution for distinguishing different species and intra-species genomic variations. In this study, we tested the value of full-length chloroplast genomes (cpDNAs) as super barcodes for distinguishing diatom species, by constructing cpDNAs of 11 strains of the class Bacillariophyceae, including Nitzschia ovalis, Nitzschia traheaformis, Cylindrotheca spp., Psammodictyon constrictum, Bacillaria paxillifer, two strains of Haslea tsukamotoi, Haslea avium, Navicula arenaria, and Pleurosigma sp. Comparative analysis of cpDNAs revealed that cpDNAs were not only adequate for resolving different species, but also for enabling recognition of high levels of genome rearrangements between cpDNAs of different species, especially for species of the genera Nitzschia, Cylindrotheca, Navicula and Haslea. Additionally, comparative analysis suggested that the positioning of species in the genus Haslea should be transferred to the genus Navicula. Chloroplast genome-based evolutionary analysis suggested that the Bacillariophyceae species first appeared during the Cretaceous period and the diversity of species rose after the mass extinction about 65 Mya. This study highlighted the value of cpDNAs in research on the biodiversity and evolution of Bacillariophyceae species, and, with the construction of more cpDNAs representing additional genera, deeper insight into the biodiversity and evolutionary relationships of Bacillariophyceae species will be gained.

Determination of Marine Biotoxins Contamination Level of Mussel (Perna Perna) (Linne, 1758) from the Mamelles Bay, Dakar

This study evaluating marine biotoxins contamination level of mussel ( Perna Perna ) in the Mamelles Bay (Ouakam) of Dakar is the first report in Senegal. It took place over one year (from March 2018 to February 2019). Liquid chromatography with mass spectrometry (LC-MS-MS) reference method (Regulation (EC) 15/2011 of 10 January 2011) was used to quantify marine biotoxins. Okadaic acid (OA) and its esters are the most problematic of all the researched biotoxins. They are present throughout most of the year, except September and November, with an average monthly concentration of 163 µg/kg, slightly above the regulatory limit (160 µg/kg). The sanitary status of the mussel shows two peaks of contamination, the first of which occurs in the rainy season (August) and the second in the cold season (December), with values equal to 654 and 802 µg/kg respectively 4 to 5 times higher than the regulatory threshold set by Regulation (EC) No 853/2004 of 29 April 2004 supplemented by Regulation (EU) No 786/2013 amending its Annex III and Senegalese Order No 07951 of 12 May 2017. These two peaks coincide with (i) the wintering period, marked by continental land-based inputs due to rainwater runoff, but also with the temperature rise, or (ii) the cold period with the appearance of upwelling (upwelling of cold water, rich in nutrient salts). In addition to the chemical analyses carried out on the mussel, the research work on phytoplankton and the surveys of physicochemical parameters carried out on the water at the collection site show (i) the existence of toxic algae of the Dinophysis genus and Gambierdiscus , in June, i.e., one to two months before the first peak of contamination of the Perna perna by AO; (ii) also a coincidence between the appearance of these phenomena and variations in surface water temperature and salinity, which are determining factors in the appearance and development of harmful algal blooms. Concerning the other biotoxins investigated, in particular AZA and yessotoxins, it was noted that AZA was absent throughout the year, unlike yessotoxins, which were found in the flesh of Perna perna at concentrations below the regulatory limit set at 3750 µg/kg. The maximum being 51 µg/kg obtained in June, i.e., 73 times lower than the regulatory threshold. In the light of the results obtained, it appears that the periods of high contamination are the winter period and the upwelling period, which could lead to closure measures to guarantee the safety of the mussels. It would be interesting to extend the study to all other bivalve mollusks and gastropods, to carry out an inventory and quantify the toxic microalgae present in the water. To this end, the effectiveness of purification techniques would be tested. Keywords: Mussel ( Perna perna ), Marine biotoxins, Toxic microalgae, Mamelles, Dakar. DOI: 10.7176/FSQM/117-04 Publication date: July 31 st 2022

A Meta-Analysis on Harmful Algal Bloom (HAB) Detection and Monitoring: A Remote Sensing Perspective

Algae serves as a food source for a wide range of aquatic species; however, a high concentration of inorganic nutrients under favorable conditions can result in the development of harmful algal blooms (HABs). Many studies have addressed HAB detection and monitoring; however, no global scale meta-analysis has specifically explored remote sensing-based HAB monitoring. Therefore, this manuscript elucidates and visualizes spatiotemporal trends in HAB detection and monitoring using remote sensing methods and discusses future insights through a meta-analysis of 420 journal articles. The results indicate an increase in the quantity of published articles which have facilitated the analysis of sensors, software, and HAB proxy estimation methods. The comparison across multiple studies highlighted the need for a standardized reporting method for HAB proxy estimation. Research gaps include: (1) atmospheric correction methods, particularly for turbid waters, (2) the use of analytical-based models, (3) the application of machine learning algorithms, (4) the generation of harmonized virtual constellation and data fusion for increased spatial and temporal resolutions, and (5) the use of cloud-computing platforms for large scale HAB detection and monitoring. The planned hyperspectral satellites will aid in filling these gaps to some extent. Overall, this review provides a snapshot of spatiotemporal trends in HAB monitoring to assist in decision making for future studies.

Individual Microcystis colonies harbour distinct bacterial communities that differ by Microcystis oligotype and with time.

Interactions between bacteria and phytoplankton in the phycosphere have impacts at the scale of whole ecosystems, including the development of harmful algal blooms. The cyanobacterium Microcystis causes toxic blooms that threaten freshwater ecosystems and human health globally. Microcystis grows in colonies that harbour dense assemblages of other bacteria, yet the taxonomic composition of these phycosphere communities and the nature of their interactions with Microcystis are not well characterized. To identify the taxa and compositional variance within Microcystis phycosphere communities, we performed 16S rRNA V4 region amplicon sequencing on individual Microcystis colonies collected biweekly via high-throughput droplet encapsulation during a western Lake Erie cyanobacterial bloom. The Microcystis phycosphere communities were distinct from microbial communities in whole water and bulk phytoplankton seston in western Lake Erie but lacked 'core' taxa found across all colonies. However, dissimilarity in phycosphere community composition correlated with sampling date and the Microcystis 16S rRNA oligotype. Several taxa in the phycosphere were specific to and conserved with Microcystis of a single oligotype or sampling date. Together, this suggests that physiological differences between Microcystis strains, temporal changes in strain phenotypes, and the composition of seeding communities may impact community composition of the Microcystis phycosphere.

Effects of mycosubtilin homolog algicides from a marine bacterium, Bacillus sp. SY-1, against the harmful algal bloom species Cochlodinium polykrikoides.

The marine bacterium, Bacillus sp. SY-1, produced algicidal compounds that are notably active against the bloom-forming alga Cochlodinium polykrikoides. We isolated three algicidal compounds and identified these as mycosubtilins with molecular weights of 1056, 1070, and 1084 (designated MS 1056, 1070, and 1084, respectively), based on amino acid analyses and 1H, 13C, and two-dimensional nuclear magnetic resonance spectroscopy, including 1H-15N heteronuclear multiple bond correlation analysis. MS 1056 contains a β-amino acid residue with an alkyl side chain of C15, which has not previously been seen in known mycosubtilin families. MS 1056, 1070, and 1084 showed algicidal activities against C. polykrikoides with 6-h LC50 values of 2.3 ± 0.4, 0.8 ± 0.2, and 0.6 ± 0.1 μg/ml, respectively. These compounds also showed significant algicidal activities against other harmful algal bloom species. In contrast, MS 1084 showed no significant growth inhibitory effects against other organisms, including bacteria and microalgae, although does inhibit the growth of some fungi and yeasts. These observations imply that the algicidal bacterium Bacillus sp. SY-1 and its algicidal compounds could play an important role in regulating the onset and development of harmful algal blooms in natural environments.

Functional significance of phylogeographic structure in a toxic benthic marine microbial eukaryote over a latitudinal gradient along the East Australian Current.

Genetic diversity in marine microbial eukaryotic populations (protists) drives their ecological success by enabling diverse phenotypes to respond rapidly to changing environmental conditions. Despite enormous population sizes and lack of barriers to gene flow, genetic differentiation that is associated with geographic distance, currents, and environmental gradients has been reported from planktonic protists. However, for benthic protists, which have reduced dispersal opportunities, phylogeography and its phenotypic significance are little known. In recent years, the East Australian Current (EAC) has intensified its southward flow, associated with the tropicalization of temperate waters. Benthic harmful algal species have been increasingly found in south‐eastern Australia. Yet little is known about the potential of these species to adapt or extend their range in relation to changing conditions. Here, we examine genetic diversity and functional niche divergence in a toxic benthic dinoflagellate, Ostreopsis cf. siamensis, along a 1,500 km north–south gradient in southeastern Australia. Sixty‐eight strains were established from eight sampling sites. The study revealed long‐standing genetic diversity among strains established from the northern‐most sites, along with large phenotypic variation in observed physiological traits such as growth rates, cell volume, production of palytoxin‐like compounds, and photophysiological parameters. Strains from the southern populations were more uniform in both genetic and functional traits, and have possibly colonized their habitats more recently. Our study reports significant genetic and functional trait variability in a benthic harmful algal species, indicative of high adaptability, and a possible climate‐driven range extension. The observed high trait variation may facilitate development of harmful algal blooms under dynamic coastal environmental conditions.

Harmful Algal Blooms Associated with Volcanic Eruptions in Indonesia and Philippines for Korean Fishery Damage

Harmful Algal Blooms (HAB) were analyzed to trace the outbreak of dinoflagellate Cochlonidium polykrikoides on the Korean coast from 1993 to 2019 along with relationship to volcanic eruptions. Parameters associated with blooms and fishery damage were sunspot number, El Niño/La Niña events, Kuroshio Current, and volcanic eruptions in the South China Sea including Indonesia and the Philippines. HAB development was halted in seawater due to the sulfur compounds (H2S, SO2, sulfates) from volcanic eruptions inducing the deficiency of the dissolved iron (Fe) in the seawater. Cochlonidium polykrikoides blooms could be predicted by the minimal sunspot number during La Niña event or weak volcanic eruptions in Indonesia and the Philippines. On line monitoring of HAB was suggested using a prototype detector of Cochlonidium polykrikoides at wavelength of 300 nm with the concentration linearity (R2 = 0.9972) between 1000 and 6000 cells/ml. HABs on the Korean coast were negligible when there were volcanic eruptions in either Indonesia or Philippines from May to August. Fishery damage was linearly proportional (R2 = 0.2986) to the maximal concentration of HAB while 5000 cells/ml was the minimal concentration of HAB with high linearity (R2 = 0.7629), caused by old cysts of Cochlonidium polykrikoides on the Korean coast rather than the fresh ones carried by the Kuroshio Current from the Philippines. Fishery damage was reversely proportional to the number of sunspots; the maximal number of sunspots induced frequent volcanic eruption in Indonesia and the Philippines for retardation of HAB with less fishery damage in Korea while the minimal number of sunspots caused less volcanic eruptions for thereby enhancing HAB resulting in more fishery damage. It was proposed that a yellow LED be used at 590 nm as a photochemical expellent as well as H2S gas bubbling at a 0.5 meter depth on the surface of the fish cage to inactivate chemically Cochlonidium polykrikoides due to the deficiency of essential iron in the seawater. In addition, the physical method of blanketing the cage cloth with smaller pore diameter than that of HAB was used for prevention of Cochlonidium polykrikoides penetrating into the fish cage.

Algal toxins in Alaskan seabirds: Evaluating the role of saxitoxin and domoic acid in a large-scale die-off of Common Murres

Elevated seawater temperatures are linked to the development of harmful algal blooms (HABs), which pose a growing threat to marine birds and other wildlife. During late 2015 and early 2016, a massive die-off of Common Murres (Uria aalge; hereafter, murres) was observed in the Gulf of Alaska coincident with a strong marine heat wave. Previous studies have documented illness and death among seabirds resulting from exposure to the HAB neurotoxins saxitoxin (STX) and domoic acid (DA). Given the unusual mortality event, corresponding warm water anomalies, and recent detection of STX and DA throughout coastal Alaskan waters, HABs were identified as a possible factor of concern. To evaluate whether algal toxins may have contributed to murre deaths, we tested for STX and DA in a suite of tissues obtained from beach-cast murre carcasses associated with the die-off as well as from apparently healthy murres and Black-legged Kittiwakes (Rissa tridactyla; hereafter, kittiwakes) sampled in the preceding and following summers. We also tested forage fish and marine invertebrates collected in the Gulf of Alaska in 2015–2017 to evaluate potential sources of HAB toxin exposure for seabirds. Saxitoxin was present in multiple tissue types of both die-off (36.4 %) and healthy (41.7 %) murres and healthy kittiwakes (54.2 %). Among birds, we detected the highest concentrations of STX in liver tissues (range 1.4–10.8 μg 100 g−1) of die-off murres. Saxitoxin was relatively common in forage fish (20.3 %) and invertebrates (53.8 %). No established toxicity limits currently exist for seabirds, but concentrations of STX in birds and forage fish in our study were lower than values reported from most other bird die-offs in which STX intoxication was causally linked. We detected low concentrations of DA in a single bird sample and in 33.3 % of invertebrates and 4.0 % of forage fish samples. Although these results do not support the hypothesis that acute exposure to STX or DA was a primary factor in the 2015–2016 mortality event, additional information about the sensitivity of murres to these toxins is needed before we can discount their potential role in the die-off. The widespread occurrence of STX in seabirds, forage fish, and invertebrates in the Gulf of Alaska indicates that algal toxins should be considered in future assessments of seabird health, especially given the potential for greater occurrence of HABs in the future.

Modeling harmful algal blooms in a changing climate

This review assesses harmful algal bloom (HAB) modeling in the context of climate change, examining modeling methodologies that are currently being used, approaches for representing climate processes, and time scales of HAB model projections. Statistical models are most commonly used for near-term HAB forecasting and resource management, but statistical models are not well suited for longer-term projections as forcing conditions diverge from past observations. Process-based models are more complex, difficult to parameterize, and require extensive calibration, but can mechanistically project HAB response under changing forcing conditions. Nevertheless, process-based models remain prone to failure if key processes emerge with climate change that were not identified in model development based on historical observations. We review recent studies on modeling HABs and their response to climate change, and the various statistical and process-based approaches used to link global climate model projections and potential HAB response. We also make several recommendations for how the field can move forward: 1) use process-based models to explicitly represent key physical and biological factors in HAB development, including evaluating HAB response to climate change in the context of the broader ecosystem; 2) quantify and convey model uncertainty using ensemble approaches and scenario planning; 3) use robust approaches to downscale global climate model results to the coastal regions that are most impacted by HABs; and 4) evaluate HAB models with long-term observations, which are critical for assessing long-term trends associated with climate change and far too limited in extent.

Assessing risks and mitigating impacts of harmful algal blooms on mariculture and marine fisheries

AbstractAquaculture is the fastest growing food sector globally and protein provisioning from aquaculture now exceeds that from wild capture fisheries. There is clear potential for the further expansion of marine aquaculture (mariculture), but there are associated risks. Some naturally occurring algae can proliferate under certain environmental conditions, causing deoxygenation of seawater, or releasing toxic compounds (phycotoxins), which can harm wild and cultured finfish and shellfish, and also human consumers. The impacts of these so‐called harmful algal blooms (HABs) amount to approximately 8 $billion/yr globally, due to mass mortalities in finfish, harvesting bans preventing the sale of shellfish that have accumulated unsafe levels of HAB phycotoxins and unavoided human health costs. Here, we provide a critical review and analysis of HAB impacts on mariculture (and wild capture fisheries) and recommend research to identify ways to minimise their impacts to the industry. We examine causal factors for HAB development in inshore versus offshore locations and consider how mariculture itself, in its various forms, may exacerbate or mitigate HAB risk. From a management perspective, there is considerable scope for strategic siting of offshore mariculture and holistic Environmental Approaches for Aquaculture, such as offsetting nutrient outputs from finfish farming, via the co‐location of extractive shellfish and macroalgae. Such pre‐emptive, ecosystem‐based approaches are preferable to reactive physical, chemical or microbiological control measures aiming to remove or neutralise HABs and their phycotxins. To facilitate mariculture expansion and long‐term sustainability, it is also essential to evaluate HAB risk in conjunction with climate change.