Occurrence Of Harmful Algal Blooms Research Articles

Identification of potentially harmful microalgal species and eutrophication status update in Benoa Bay, Bali, Indonesia

Harmful algal blooms (HABs) often occurred in a eutrophicated coastal areas, which causes ecological, economic, and health problems to the ecosystem and coastal communities. Benoa Bay is a coastal ecosystem in Indonesia which threatened by eutrophication and vulnerable to the occurrence of HABs in the future. This study focuses on identifying the potential harmful microalgal species and updating the trophic status in Benoa Bay. Sampling was done during the dry season in 2017 from 30 stations. Tewnty-nine species of phytoplankton were identified in Benoa Bay. Coscinodiscus spp., Pseudo-nitzschia spp., Skeletonema spp., Chaetoceros spp., Rhizosolenia spp., and Ceratium spp., were categorized as potentially harmful microalgal. Among those, Coscinodiscus spp. was the most abundant and widely distributed species in Benoa Bay. Phytoplankton cell density was highest in the area between Suwung Landfill and Floating Net Cage (16,584 cells L-1), while the lowest (20 cells L-1) was found in the Sama River estuary. The tb-RDA analysis showed salinity and dissolved oxygen percentage saturation (D%O) were two most significant factor that drives the density and distribution of phytoplankton species in Benoa Bay. In general, Benoa Bay was in the oligotrophic state based on phytoplankton abundance and chlorophyll-a concentration, while in mesotrophic states based on TRIX. The occurrence of some potentially harmful microalgal species, along with relatively high trophic levels in Benoa Bay, requires serious attention to prevent damages from any HABs event in the future.

Harmful Algal Blooms in Aquaculture Systems in Ngerengere Catchment, Morogoro, Tanzania: Stakeholder's Experiences and Perception.

The aquaculture sector has experienced fast growth as a result of livelihood diversification initiatives among small-scale farmers in Tanzania. Regrettably, the dynamics of harmful algal blooms (HABs) have been overlooked despite the noticeable forcing of climate variability, the interaction between social-economic activities, and domestic water supply reservoirs. This study aimed at surveying the occurrence, experiences, and perceptions of HABs in aquaculture systems from stakeholders in the Ngerengere catchment, Morogoro, Tanzania. A cross-sectional survey focus group discussion (FDG), key informant interviews, and anecdotal observation were adopted. A convenient and purposive sample population was drawn from pond owners, registered water users, and government officials in the catchment. For data analysis, descriptive statistics and constant comparison were performed. Most respondents (95%) were able to recognize the image of blooms displayed. Approximately 70% of the respondents agreed that water quality has deteriorated over time, and blooms occur during the dry season. Further, 60% of the respondents agreed that water pollution is a serious problem attributed to sources other than industrial discharge. There was no consensus regarding the health impacts associated with HABs. Raising awareness on HABs is of paramount importance as it will provide the basis for the development of HABs management framework and health risk assessment.

Reconstructing primary production in a changing estuary: A mass balance modeling approach

AbstractEstuarine primary production (PP) is a critical rate process for understanding ecosystem function and response to environmental change. PP is fundamentally linked to estuarine eutrophication, and as such should respond to ongoing efforts to reduce nutrient inputs to estuaries globally. However, concurrent changes including warming, altered hydrology, reduced input of sediments, and emergence of harmful algal blooms (HABs) could interact with nutrient management to produce unexpected changes in PP. Despite its fundamental importance, estuarine PP is rarely measured. We reconstructed PP in the York River Estuary with a novel mass balance model based on dissolved inorganic nitrogen (DIN) for the period 1994–2018. Modeled PP compared well to previous estimates and demonstrated a long‐term increase and down‐estuary shift over the study period. This increase occurred despite reductions in discharge, flushing time, DIN loading, and DIN standing stock over the same period. Increased PP corresponded to increased water temperature, decreased turbidity and light attenuation, and increased photic depth and assimilation ratio, suggesting that phytoplankton in the York River Estuary have become more efficient at converting nutrients into biomass primarily due to a release from light limitation. The increase in PP also coincided with the increasing occurrence of late summer HABs in the lower York River Estuary, including the emergence of a second bloom‐forming dinoflagellate in 2007. Results demonstrate how changes concurrent with nutrient management could alter expected system responses and illustrate the utility of the mass balance approach for estimating critical rate processes like PP in the absence of observations.

The influence of estuary eutrophication on the benthic diatom community: a molecular approach

The occurrence of harmful algal blooms (HABs) is increasing in frequency and intensity in South African estuaries because of eutrophication. This study used DNA metabarcoding to identify the benthic diatom community structure in the eutrophic Sundays Estuary. The recurrent HAB phytoplankton species Heterosigma akashiwo was recorded at bloom concentrations (∼100 µg Chl a l−1) in the brackish, vertically stratified middle reaches of the estuary. In contrast, microphytobenthos biomass increased towards the upper reaches in response to elevated availability of total oxidised nitrogen (NOx) and increased sediment stability. A total of 76 diatom species were identified using the molecular technique. Seven known nutrient-tolerant diatom species indicate a preference for either ammonium or NOx enrichment. Benthic diatom community diversity (H′ < 1) and evenness (J′ < 0.25) were low in the brackish middle reaches of the estuary, where the HABs decreased available light. Heterosigma akashiwo has been found in previous studies to suppress the growth of co-occurring taxa. Future research efforts should focus on verifying this relationship over seasonal timescales given the dominance of H. akashiwo in spring/summer. As the persistently nutrient-enriched state and stable flow conditions of the Sundays Estuary is the key driver of change, management efforts should be geared towards re-establishing the estuary’s natural flow variations and to measures that can mitigate nutrient pollution.

Phosphorus Inventory for the Conterminous United States (2002-2012).

Published reports suggest efforts designed to prevent the occurrence of harmful algal blooms and hypoxia by reducing non-point and point source phosphorus (P) pollution are not delivering water quality improvements in many areas. Part of the uncertainty in evaluating watershed responses to management practices is the lack of standardized estimates of phosphorus inputs and outputs. To assess P trends across the conterminous United States, we compiled an inventory using publicly available datasets of agricultural P fluxes, atmospheric P deposition, human P demand and waste, and point source discharges for 2002, 2007, and 2012 at the scale of the 8-digit Hydrologic Unit Code subbasin (~1,800 km2). Estimates of agricultural legacy P surplus accumulated from 1945 to 2001 were also developed. Fertilizer and manure inputs were found to exceed crop removal rates by up to 50% in many agricultural regions. This excess in inputs has led to the continued accumulation of legacy P in agricultural lands. Atmospheric P deposition increased throughout the Rockies, potentially contributing to reported increases in surface water P concentrations in undisturbed watersheds. In some urban areas, P fluxes associated with human waste and non-farm fertilizer use has declined despite population growth, likely due, in part, to various sales bans on P-containing detergents and fertilizers. Although regions and individual subbasins have different contemporary and legacy P sources, a standardized method of accounting for large and small fluxes and ready to use inventory numbers provide essential infromation to coordinate targeted interventions to reduce P concentrations in the nation's waters.

Machine learning based marine water quality prediction for coastal hydro-environment management

During the past three decades, harmful algal blooms (HAB) events have been frequently observed in marine waters around many coastal cities in the world including Hong Kong. The increasing occurrence of HAB has caused acute influences and damages on water environment and marine aquaculture with millions of monetary losses. For example, the Tolo Harbour is one of the most affected areas in Hong Kong, where more than 30% HAB occurred. In order to forewarn the potential HAB incidents, the machine learning (ML) methods have been increasingly resorted in modelling and forecasting water quality issues. In this study, two different ML methods – artificial neural networks (ANN) and support vector machine (SVM) – are implemented and improved by introducing different hybrid learning algorithms for the simulations and comparative analysis of more than 30-year measured data, so as to accurately forecast algal growth and eutrophication in Tolo Harbour in Hong Kong. The application results show the good applicability and accuracy of these two ML methods for the predictions of both trend and magnitude of the algal growth. Specifically, the results reveal that ANN is preferable to achieve satisfactory results with quick response, while the SVM is suitable to accurately identify the optimal model but taking longer training time. Moreover, it is demonstrated that the used ML methods could ensure robustness to learn complicated relationship between algal dynamics and different coastal environmental variables and thereby to identify significant variables accurately. The results analysis and discussion of this study also indicate the potentials and advantages of the applied ML models to provide useful information and implications for understanding the mechanism and process of HAB outbreak and evolution that is helpful to improving the water quality prediction for coastal hydro-environment management.

Trophic triage: a tiered eutrophication vulnerability screening tool for lakes in sparsely monitored regions

Johnston L, Hiscock A, Holmes B, Bermarija T, Scott R, Sinclair A, Jamieson R. 2020. Trophic triage: a tiered eutrophication vulnerability screening tool for lakes in sparsely monitored regions. Lake Reserv Manage. 37:214–226. Eutrophication and the occurrence of harmful algal blooms (HABs) have been observed in lakes throughout North America. Here, we developed a high-level lake screening tool for characterizing eutrophication vulnerability in sparsely monitored regions. The screening tool involves a desktop study (Tier 1) to classify the vulnerability of lakes to eutrophication as either low, moderate, or high vulnerability. A subset of lakes is then identified from this initial assessment for a preliminary water quality sampling program to confirm the desktop evaluation (Tier 2). From this evaluation, lakes in a final subset undergo a comprehensive sampling program to establish final vulnerability levels (Tier 3). The screening tool was initially developed and demonstrated for lakes within the Municipality of Cumberland County, Nova Scotia, Canada. Five lakes, spanning a range of land uses, morphologies, and watershed settings, were subjected to a detailed water quality monitoring program to help refine factors and thresholds in the screening tool. Tier 2 and Tier 3 were then applied to the 5 study lakes to demonstrate the complete screening process. Tier 1 of the screening tool was further validated on an additional 29 lakes in Nova Scotia, and performed as intended for the majority of lakes, predicting the same or higher trophic state than the one currently measured for 25 of the 29 lakes. For the 4 lakes with trophic states that were underpredicted, the vulnerability level was still correctly predicted. The screening tool proved to be a robust approach for identifying lakes that are vulnerable to eutrophication, and for prioritizing monitoring activities.

Common fate of sister lakes in Hulunbuir Grassland: Long-term harmful algal bloom crisis from multi-source remote sensing insights

With the increasing impact of drought and anthropogenic c activities, middle and high latitude lakes are increasingly facing exacerbated eutrophication. The sister lakes Hulun Lake and Buir Lake, the former located in the Hulunbuir Grassland in northeast China and the latter shared by China and Mongolia, have been exposed to outbreaks of harmful algal blooms (HABs) of varying degrees. In this study, multi-source remote sensing technologies were utilized to explore the essential factors causing HAB occurrences in the Hulun Basin. First, a simplified adjusted floating algae index (AFAI) algorithm was applied to invert the HAB sequence from 1984 to 2019. The results show that large-scale HABs were detected in both lakes on or close to the same days in 1984, 1999, and 2013. From a long-term perspective, the HAB events of Hulun Lake are more serious and intractable than those of Buir Lake in terms of outbreak frequency, duration, and scale. Furthermore, the effects of meteorological and hydrological conditions were evaluated quantitatively. In situ sampling of the two lakes highlights the limiting effect of nutrients on the algae flooding in Buir Lake with perennial outflow. In contrast, Hulun Lake turned into an internal flow lake without outlets from 2000 to 2012 and the decreasing water volume stimulated the accumulation of total nitrogen (TN) and phosphorus (TP), with averages of 2.36 and 0.21 mg/L, respectively. Analysis of the comprehensive driving factors demonstrates that the level of exogenous nutrients caused a difference in the severity of the HAB event between the sister lakes, which are largely determined by drought and eco-unfriendly anthropogenic activities. Our work emphasizes the pivotal role of substantial increases of nutrient loads and stricter regulations are necessary to curb further deterioration of this situation.

Factors affecting harmful algal bloom occurrence in a river with regulated hydrology

Study regionThe Geum River Basin, South Korea. Study focusIn-stream structures potentially amplify harmful algal blooms (HABs) by increasing water residence time and deteriorating water quality. Removal or gate control of in-stream structures is considered a management tool to reduce HAB occurrence. Prior evaluation, however, is necessary to assess the effect of structural modifications to control HABs. This study focused on factors affecting HAB occurrence relative to the operation of 3 in-stream weirs using a 3-dimensional hydrodynamic and water quality model. New hydrological insights for the study regionPhysical changes due to gate opening could not guarantee an improvement in water quality and reduction in cyanobacterial biomass. Cyanobacteria, a major component of HABs, decreased in the upstream reach but conditions deteriorated downstream during summer. Maximum cyanobacteria concentrations in the downstream reach almost doubled during summer with the open-gate scenario. Although the open-gate flow allowed less time for algal growth, (1) increased light availability with decreased water depth and (2) dissolved phosphorus, which was not depleted upstream, promoted cyanobacterial growth. Consequently, the proliferation of cyanobacterial blooms downstream was due to conditions that enhanced algal growth, despite reduced hydraulic residence time under the open-gate scenario. This analysis indicates that hydrologic regulation may not improve water quality and also may affect spatial and temporal distribution of cyanobacteria in the system. Reducing HABs will likely require a reduction in the pollution load.

Mitigating antibiotic pollution using cyanobacteria: Removal efficiency, pathways and metabolism

The occurrence of pharmaceuticals and personal care products (PPCPs) in wastewater poses huge environmental threats, even at trace concentrations, and novel approaches are urged due to the inefficiencies of conventional wastewater treatment plants, especially when processing contaminants at high concentrations. Meanwhile, another widespread problem in the aquatic domain is the occurrence of harmful algal blooms (HABs) which cause serious damage to the ecosystem, but have rarely been investigated for possible valorization. This study investigated the possibilities, mechanisms, and effects of toxin release of using a harmful cyanobacterial species, Microcystis aeruginosa (M. aeruginosa), in order to remove the widely used drug, tetracycline, at high concentration. The results were compared with the performance obtained by the use of the hitherto generally-selected chlorophyte alga Chlorella pyrenoidosa (C. pyrenoidosa) for tetracycline concentrations of 10-100 mg L-1. M. aeruginosa exhibited a much more effective and rapid tetracycline removal (over 98.0% removal in 2 days) than did C. pyrenoidosa (36.7%-93.9% in 2 days). A comprehensive kinetic investigation into probable removal pathways indicated that, theoretically, bio-remediation dominated the process by M. aeruginosa (71.6%), while only accounting for 20.5% by C. pyrenoidosa. Both microalgae promoted the hydrolysis of tetracycline under conditions of increased pH and inhibited abiotic photolytic reactions by the shading effect to the water column, when compared with control experiments. Although identical degradation by-products were identified from treatments by both microalgal species, distinct by-products were also confirmed, unique to each treatment. Moreover, the growth of M. aeruginosa biomass exhibited strong tolerance to tetracycline exposure and released significantly lower levels of microcystin-LR, compared with the control systems. This study supports the possibility of reusing HABs species for the effective remediation of antibiotics at high concentrations. We have further suggested possible mechanisms for remediation and demonstrated control of toxin release.

Developing an Atlas of Harmful Algal Blooms in the Red Sea: Linkages to Local Aquaculture

Harmful algal blooms (HABs) are one of the leading causes of biodiversity loss and alterations to ecosystem services. The Red Sea is one of the least studied large marine ecosystems (LMEs), and knowledge on the large-scale spatiotemporal distribution of HABs remains limited. We implemented the recently developed remote sensing algorithm of Gokul et al. (2019) to produce a high-resolution atlas of HAB events in the Red Sea and investigated their spatiotemporal variability between 2003 and 2017. The atlas revealed that (i) the southern part of the Red Sea is subject to a higher occurrence of HABs, as well as long-lasting and large-scale events, in comparison to the northern part of the basin, and (ii) the Red Sea HABs exhibited a notable seasonality, with most events occurring during summer. We further investigated the potential interactions between identified HAB events and the National Aquaculture Group (NAQUA), Al-Lith (Saudi Arabia)—the largest aquaculture facility on the Red Sea coast. The results suggest that the spatial coverage of HABs and the elevated chlorophyll-a concentration (Chl-a) (&gt; 1 mg m−3; a proxy for high nutrient concentration), in the coastal waters of Al-Lith during summer, increased concurrently with the local aquaculture annual production over a nine-year period (2002–2010). This could be attributed to excessive nutrient loading from the NAQUA facility’s outfall, which enables the proliferation of HABs in an otherwise oligotrophic region during summer. Aquaculture is an expanding, high-value industry in the Kingdom of Saudi Arabia. Thus, a wastewater management plan should ideally be implemented at a national level, in order to prevent excessive nutrient loading. Our results may assist policy-makers’ efforts to ensure the sustainable development of the Red Sea’s coastal economic zone.

A count model approach on the occurrences of harmful algal blooms (HABs) in Ambon Bay

Climate change and increased anthropogenic activities have resulted in an imbalance in the aquatic ecosystem and have triggered the appearance of harmful algae in Ambon Bay, Indonesia. This study aims to identify the phytoplankton community structure, measure physicochemical water quality (temperature, salinity, pH, DO, nitrate and phosphate) in Ambon Bay, and create a prediction model to estimate the occurrence of harmful algal bloom based on these water quality measures. The results of the statistical count model (Poisson regression) showed that three phytoplankton divisions were observed: Bacillariophyta, Dinophyta and Cyanophyta. Of these, Bacillariophyceae were the most abundant. The only species of the Cyanophyta division identified was Trichodesmium, a type of harmful algae that can produce high biomass that may clog fish gills and generate low oxygen. Our Poisson regression model suggested that all water quality factors measured affected the abundance of Trichodesmium in Ambon Bay and that, moreover, rising levels of nitrate and salinity will cause a surge in Trichodesmium.

The Effects of Modified Clay on Abalone (Haliotis discus hannai) Based on Laboratory and Field Experiments.

The abalone industry has suffered immense economic losses due to the occurrence of harmful algal blooms (HABs). Among the methods for mitigating HABs, modified clay is considered the most promising strategy and has been successfully used for field applications in many countries, and its environmental effects have become a subject of global concern. The effects of modified clay on the survival, growth, nutritional quality, and oxidative stress indicators of abalone were studied based on both laboratory and field experiments. The results showed that modified clay at 3-10 times the concentrations used for HAB treatment did not affect the survival of abalone. During the laboratory experiments, the increases in abalone shell length and weight nonsignificantly decreased with increasing concentrations of modified clay at 1-15 d, whereas the weight of abalone in the experimental groups increased rapidly during the recovery period at 16-30 d. The growth and nutrition qualities of abalone in field experiments showed negligible differences between the control and experimental groups. Catalase (CAT) activity in the hepatopancreas and superoxide dismutase (SOD) activity in the gills were significantly affected by certain concentrations of modified clay at individual time points, whereas the malondialdehyde (MDA) content decreased in all experimental groups within 96 h. The removal of bacteria and the mitigation of water quality decline were among the effects of modified clay that contributed to the decrease in MDA content. The present study showed that modified clay had no obvious adverse effects on the survival, growth, quality, or oxidative stress indicators of abalone at the experimental concentrations, thus providing a reference for the field application of modified clay in typical aquaculture areas. Environ Toxicol Chem 2020;39:2065-2075. © 2020 SETAC.

Water-lifting aerator reduces algal growth in stratified drinking water reservoir: Novel insights into algal metabolic profiling and engineering applications

Water-lifting aerator (WLA) which was developed by Professor Tinglin Huang at Xi’an University of Architecture and Technology, China has multi-functional water quality improvement that significantly inhibits the occurrence of harmful algal blooms (HABs) in deep drinking water reservoirs. However, the biological mechanism of WLA to the suppress algal growth has not been comprehensively understood. Here, the cellular mechanism that allows WLA to control HABs was explored based on the combination of both laboratory simulation and field investigation. Under simulated hydrodynamic conditions, the results showed that the cell density, chlorophyll a content, chlorophyll fluorescence parameters, and dehydrogenase activity in Microcystis aeruginosa all peaked under light conditions at 25 °C. The metabolic activity of M. aeruginosa varied significantly under low temperature at 6 °C and light conditions when cultured for 48 h. The extracellular organic matter (EOM) and intracellular organic matter (IOM) contents of M. aeruginosa were both resolved into three components. Moreover, the total fluorescence intensities from EOM and IOM both peaked under light conditions at 25 °C. The field investigation showed that the growth of algae was decreased significantly in Lijiahe drinking water reservoir with WLA application. The chlorophyll fluorescence parameters decreased significantly after vertical mixing, thereby indicating that the WLA weakened the photosynthetic ability and reduced the biological activity of algae in situ. In addition, the WLA significantly affected the vertical distribution of the phytoplankton community composition. Altogether, these results shed new lights on understanding the control of algal blooms by WLA in stratified drinking water reservoirs. WLA has broad prospect of engineering applications, which can control algal blooms of water supply resources in situ, therefore, reduce the content of disinfection by-products in drinking water treatment plants.

Impact of algal organic matter on the performance, cyanotoxin removal, and biofilms of biologically-active filtration systems

The occurrence of harmful algal blooms dominated by toxic cyanobacteria has induced continuous loadings of algal organic matter (AOM) and toxins in drinking water treatment plants. However, the impact of AOM on the active biofilms and microbial community structures of biologically-active filtration (BAF), which directly affects the contaminant removal, is not well understood. In this study, we systematically examined the effects of AOM on BAF performance and bacterial biofilm formation over 240 days, tracing the removal of specific AOM components, a cyanotoxin [microcystin-LR (MC-LR)], and microbial community responses. The component analysis (excitation and emission matrix analysis) results for AOM revealed that terrestrial humic-like substances showed the highest removal among all the identified components and were strongly correlated to MC-LR removal. In addition, reduced empty bed contact time and deactivation of biofilms significantly decreased BAF performances for both AOM and MC-LR. The active biofilm, bacterial community structure, and mlrA gene (involved in microcystin degradation) abundance demonstrated that bacterial biofilm composition responded to AOM and MC-LR, in which Rhodocyclaceae, Saprospiraceae, and Comamonadaceae were dominant. In addition, MC-LR biodegradation appeared to be more active at the top than at the bottom layer in BAF. Overall, this study provides deeper insights into the role of biofilms and filter operation on the fate of AOM and MC-LR in BAF.

Use of sea surface discoloration to monitor and discriminate the causative genera of harmful algal blooms (HABs): Practical use of digital repeat photography

Harmful algal blooms (HABs) are associated with water quality degradation, which damages fisheries, ecosystems, and public health. Consequently, techniques for detecting the occurrence of HABs have been developed globally. However, conventional techniques are unable to discriminate the causative species/genera of HABs objectively. Therefore, the aim of the present study was to develop a technique for frequently analyzing the causative genera of HAB events using repeat digital photography with a stationary device named “HABcam.” The HABcam was installed at Okigamisenishi monitoring station in the inner western area of Ariake Bay, Japan, and the digital images obtained were analyzed to quantify the sea surface color and to estimate the probability of a HAB occurrence on a daily basis using Bayes' theorem. The estimated probability of a HAB occurrence accurately discriminated a HAB occurrence or non-occurrence in the research area on 19/21 days (=90.5%) for Chattonella spp. and 7/8 days (=87.5%) for Skeletonema spp. These findings indicate that this technique can be used to objectively determine the causative genera during HAB events and to observe HABs with high accuracy and at a high frequency.

Responses of food web to hypolimnetic aeration in Lake Vesij\xe4rvi

We studied the responses of a food web, especially fish and zooplankton, to summertime aeration, pumping of oxygen-rich epilimnetic water to the hypolimnion in Lake Vesijärvi, southern Finland. The aim of hypolimnetic aeration was to reduce internal loading of phosphorus from sediment. The population of smelt (Osmerus eperlanus L.), the main planktivore of the pelagial area, collapsed during the two 1st years of aeration due to increased temperature and low oxygen concentrations in the hypolimnion. The population recovered after the 4th year of hypolimnetic aeration, when oxygen conditions were improved. Despite elevated hypolimnetic temperature, smelt reached exceptionally high abundance, which led to a significant reduction in cladoceran body size. The density of perch (Perca fluviatilis L.) increased at first, but then decreased when the proportion of smelt and cyprinids increased. Biomasses of Daphnia decreased probably as a result of the disappearance of dark, low-oxygen deep-water refuge against fish predation and low availability of nutritionally high-quality algae. Occasionally filamentous cyanobacteria, such as turbulence tolerant Planktothrix agardhii (Gomont), were abundant, suggesting deteriorated food resources for zooplankton. The responses of food web were controversial with respect to the aim of the management, which was to prevent the occurrence of harmful algal blooms.

Harmful algal blooms and associated fisheries damage in East Asia: Current status and trends in China, Japan, Korea and Russia

Occurrences of harmful algal blooms (HABs) and associated fisheries damage have been continuously monitored since the 1970s along the coasts of East Asia. Fisheries damage comprises mass mortalities of fish and shellfish mainly by harmful dinoflagellates and raphidophytes (e.g., Chattonella antiqua/marina, Cochlodinium polykrikoides and Karenia mikimotoi), and contamination of algal toxins in shellfish in particular Diarrhetic Shellfish Toxins by Dinophysis spp. and Paralytic Shellfish Toxins by Alexandrium spp. Shellfish mass mortalities due to Heterocapsa circularisquama in Hong Kong and western Japan, and fish kills by Karlodinium digitatum are unique incidents for this region, whereas C. antiqua/marina, C. polykrikoides and K. mikimotoi are common also in other regions. Time series data showed that the highest bloom numbers were recorded in 1980 (Japan), in 1998 (Korea) and in 2003 (China), followed by decreasing trends in these countries. These data suggest a shift in microalgal species composition, from dominance by diatoms to dinoflagellates after 1980s in Korea, and from diatoms to small haptophytes and cyanobacteria after 2013 in eastern Russia. HAB species composition and the changes were compared among countries, for better understanding on current status and trend of HAB species in East Asia.

Over 30 years of HABs in the Philippines and Malaysia: What have we learned?

In the Southeast Asian region, the Philippines and Malaysia are two of the most affected by Harmful Algal Blooms (HABs). Using long-term observations of HAB events, we determined if these are increasing in frequency and duration, and expanding across space in each country. Blooms of Paralytic Shellfish Toxin (PST)-producing species in the Philippines did increase in frequency and duration during the early to mid-1990s, but have stabilized since then. However, the number of sites affected by these blooms continue to expand though at a slower rate than in the 1990s. Furthermore, the type of HABs and causative species have diversified for both toxic blooms and fish kill events. In contrast, Malaysia showed no increasing trend in the frequency of toxic blooms over the past three decades since Pyrodinium bahamense was reported in 1976. However, similar to the Philippines, other PST producers such as Alexandrium minutum and Alexandrium tamiyavanichii have become a concern. No amnesic shellfish poisoning (ASP) has been confirmed in either Philippines or Malaysia thus far, while ciguatera fish poisoning cases are known from the Philippines and Malaysia but the causative organisms remain poorly studied. Since the 1990s and early 2000s, recognition of the distribution of other PST-producing species such as species of Alexandrium and Gymnodinium catenatum in Southeast Asia has grown, though there has been no significant expansion in the known distributions within the last decade. A major more recent problem in the two countries and for Southeast Asia in general are the frequent fish-killing algal blooms of various species such as Prorocentrum cordatum, Margalefidinium polykrikoides, Chattonella spp., and unarmored dinoflagellates (e.g., Karlodinium australe and Takayama sp.). These new sites affected and the increase in types of HABs and causative species could be attributed to various factors such as introduction through mariculture and eutrophication, and partly because of increased scientific awareness. These connections still need to be more concretely investigated. The link to the El Niño Southern Oscillation (ENSO) should also be better understood if we want to discern how climate change plays a role in these patterns of HAB occurrences.

Marine Heatwaves in China's Marginal Seas and Adjacent Offshore Waters: Past, Present, and Future

AbstractUnder the combined impacts of natural changes and human activities, the past, current, and future marine heatwaves (MHWs) in China's marginal seas and adjacent offshore waters (CMSOW) need a comprehensive understanding. This study provides a systematic analysis of the spatiotemporal variations using daily sea surface temperature data and simulates the future trend using 12 climate models. During 1982–2018, the mean annual total days, duration, frequency, and mean intensity of the MHWs in the CMSOW increased by 20–30 days/decade, 5–9 days/decade, 1–2 decade−1, and 0.1–0.3°C/decade, respectively (p &lt;0.01). The maximum sea surface temperature anomalies in the Bohai Sea was over 6–8°C, and the MHW's frequency, duration, and mean intensity were higher than twice the global average, which could have impacted fishery resources and occurrence of harmful algal blooms. The variations of the MHWs in the CMSOW result from the robust ocean surface warming, which is caused by increased solar radiation due to reduced cloud cover, reduced ocean heat loss from weaker wind speed, weakening but warmer Kuroshio, and strong El Niño. In the future, the areas with longer total days and duration will increase; the spatial pattern of frequency has a negative relationship with that of duration while that of mean intensity is mostly unchanged. Year 2040 is a key node for the future changes of MHW under different Representative Concentration Pathways. The trend of total days increases from fast to slow, and frequency shows an opposite trend; the duration and mean intensity rise faster after 2040.