Abstract

Harmful algal blooms (HABs) are increasing across many locations globally. Toxins from HABs can be incorporated into aerosols and transported inland, where subsequent exposure and inhalation can induce adverse health effects. However, the relationship between HAB aerosols and health outcomes remains unclear despite the potential for population-level exposures. In this review, we synthesized the current state of knowledge and identified evidence gaps in the relationship between HAB aerosols and human health. Aerosols from Karenia brevis, Ostreopsis sp., and cyanobacteria were linked with respiratory outcomes. However, most works did not directly measure aerosol or toxin concentrations and instead relied on proxy metrics of exposure, such as cell concentrations in nearby waterbodies. Furthermore, the number of studies with epidemiological designs was limited. Significant uncertainties remain regarding the health effects of other HAB species; threshold dose and the dose–response relationship; effects of concurrent exposures to mixtures of toxins and other aerosol sources, such as microplastics and metals; the impact of long-term exposures; and disparities in exposures and associated health effects across potentially vulnerable subpopulations. Additional studies employing multifaceted exposure assessment methods and leveraging large health databases could address such gaps and improve our understanding of the public health burden of HABs. Harmful algal blooms (HABs) are increasing across many locations globally. Toxins from HABs can be incorporated into aerosols and transported inland, where subsequent exposure and inhalation can induce adverse health effects. However, the relationship between HAB aerosols and health outcomes remains unclear despite the potential for population-level exposures. In this review, we synthesized the current state of knowledge and identified evidence gaps in the relationship between HAB aerosols and human health. Aerosols from Karenia brevis, Ostreopsis sp., and cyanobacteria were linked with respiratory outcomes. However, most works did not directly measure aerosol or toxin concentrations and instead relied on proxy metrics of exposure, such as cell concentrations in nearby waterbodies. Furthermore, the number of studies with epidemiological designs was limited. Significant uncertainties remain regarding the health effects of other HAB species; threshold dose and the dose–response relationship; effects of concurrent exposures to mixtures of toxins and other aerosol sources, such as microplastics and metals; the impact of long-term exposures; and disparities in exposures and associated health effects across potentially vulnerable subpopulations. Additional studies employing multifaceted exposure assessment methods and leveraging large health databases could address such gaps and improve our understanding of the public health burden of HABs. Harmful algal blooms (HABs) are diverse phenomena consisting of rapid and exponential expansions and accumulation of microalgal populations, such as cyanobacteria, diatoms, and dinoflagellates, in aquatic ecosystems.1Anderson D.M. Fensin E. Gobler C.J. et al.Marine harmful algal blooms (HABs) in the United States: history, current status and future trends.Harmful Algae. 2021; 102101975Crossref PubMed Scopus (103) Google Scholar Blooms can range from small, short-lived (days to weeks) patches to very large blooms that can cover areas spanning thousands of square kilometres and last from a few months to multiple years. The frequency, duration, severity, and geographical extent of harmful algal blooms across freshwater, estuarine, and marine ecosystems are increasing across many locations globally.2Gobler C.J. Doherty O.M. Hattenrath-Lehmann T.K. Griffith A.W. Kang Y. Litaker R.W. Ocean warming since 1982 has expanded the niche of toxic algal blooms in the North Atlantic and North Pacific oceans.Proc Natl Acad Sci U S A. 2017; 114: 4975-4980Crossref PubMed Scopus (269) Google Scholar,3Wells M.L. Karlson B. Wulff A. et al.Future HAB science: directions and challenges in a changing climate.Harmful Algae. 2020; 91101632Crossref PubMed Scopus (169) Google Scholar These shifting patterns and distributions are driven primarily by climate change and anthropogenic nutrient loading.4Griffith A.W. Gobler C.J. Harmful algal blooms: a climate change co-stressor in marine and freshwater ecosystems.Harmful Algae. 2020; 91101590Crossref PubMed Scopus (186) Google Scholar Climate change is leading to warming waters, more extreme wet/dry cycles, and acidification, leading to favourable conditions for the rapid proliferation of many HAB species.5O'Neil J.M. Davis T.W. Burford M.A. Gobler C.J. The rise of harmful cyanobacteria blooms: the potential roles of eutrophication and climate change.Harmful Algae. 2012; 14: 313-334Crossref Scopus (1470) Google Scholar Excess nutrients from large-scale agriculture, industrialization, urbanization, and population growth can further lead to altered composition of nutrients and timing that create conditions that are ideal for blooms.6Glibert P.M. Burford M.A. Globally changing nutrient loads and harmful algal blooms: recent advances, new paradigms, and continuing challenges.Oceanography. 2017; 30: 58-69Crossref Google Scholar The economic impacts of HABs on fishing and aquaculture, drinking water treatment and availability, livestock, and property values are substantial.7Adams C.M. Larkin S.L. Hoagland P. Sancewich B. Assessing the economic consequences of harmful algal blooms: a summary of existing literature, research methods, data, and information gaps.in: Harmful algal blooms: a compendium desk reference. 2018: 337-354Crossref Google Scholar HABs also pose a significant threat to public health as many HAB species can produce secondary metabolites, including potent toxins, that adversely impact many different human organ systems. The most well-understood and described routes of exposure to HABs and associated health effects include direct dermal contact leading to multiple symptoms such as rash and irritation, as well as ingestion of contaminated water or seafood resulting in gastrointestinal and neurotoxic effects.8Young N. Sharpe R.A. Barciela R. et al.Marine harmful algal blooms and human health: a systematic scoping review.Harmful Algae. 2020; 98101901Crossref PubMed Scopus (37) Google Scholar Under certain environmental conditions, toxins generated from HABs may become airborne, and subsequent inhalation of the generated aerosols can induce adverse health effects. The public health burden of HAB aerosols is likely to be considerable. One study estimated that approximately 15% of global asthma cases are attributable to the inhalation of aerosolized HAB toxins in coastal regions,9Walsh J.J. Lenes J.M. Weisberg R.H. et al.More surprises in the global greenhouse: human health impacts from recent toxic marine aerosol formations, due to centennial alterations of world-wide coastal food webs.Mar Pollut Bull. 2017; 116: 9-40Crossref PubMed Scopus (17) Google Scholar while another work found that the 2012 red tide blooms in Florida were linked with approximately 11,000 hospital admissions and 4000 emergency department visits.10Limaye V.S. Max W. Constible J. Knowlton K. Estimating the health-related costs of 10 climate-sensitive US events during 2012.Geohealth. 2019; 3: 245-265Crossref PubMed Scopus (36) Google Scholar This potential association between HAB aerosols and health outcomes remains unclear despite the potential for ubiquitous exposures for populations living near or downwind of HABs, occupations that interact directly with HABs (e.g., lifeguards), or recreational users in bodies of water with HABs. Prior reviews have focused on the health effects of a single HAB species,11Fleming L.E. Kirkpatrick B. Backer L.C. et al.Review of Florida red tide and human health effects.Harmful Algae. 2011; 10: 224-233Crossref PubMed Scopus (146) Google Scholar,12Patel S.S. Lovko V.J. Lockey R.F. Red tide: overview and clinical manifestations.J Allergy Clin Immunol Pract. 2020; 8: 1219-1223Summary Full Text Full Text PDF PubMed Scopus (14) Google Scholar or provided a broader overview of the array of symptoms associated with different HAB exposure pathways.8Young N. Sharpe R.A. Barciela R. et al.Marine harmful algal blooms and human health: a systematic scoping review.Harmful Algae. 2020; 98101901Crossref PubMed Scopus (37) Google Scholar In this review, we describe the mechanisms of exposure to aerosolized HAB toxins and the associated health effects. We first conducted a title and abstract review on articles identified through PubMed and then summarized those that investigated health outcomes with HAB aerosols as a potential source of exposure. We then summarized the mechanisms by which HAB toxins can be aerosolized, transported, and inhaled, in addition to the current methods for exposure assessment of HABs and aerosols. Finally, we synthesized the current state of knowledge and identified evidence gaps. In this section, we briefly summarize the mechanisms by which toxins from HABs can be aerosolized, transported, and inhaled (Fig. 1). Toxins from microalgae/bacteria suspended at the water surface from HABs can be emitted to the atmosphere by aerosolization. The primary mechanism of aerosolization from blooms is via the formation of spray aerosols (SA) in marine (sea spray aerosol; SSA),13Lewis E.R. Schwartz S.E. Sea salt aerosol production: mechanisms, methods, measurements, and models. American Geophysical Union, 2004Google Scholar,14De Leeuw G. Andreas E.L. Anguelova M.D. et al.Production flux of sea spray aerosol.Rev Geophys. 2011; 49Crossref Scopus (399) Google Scholar freshwater (lake spray aerosol; LSA),15May N.W. Olson N.E. Panas M. et al.Aerosol emissions from great lakes harmful algal blooms.Environ Sci Technol. 2018; 52: 397-405Crossref PubMed Scopus (48) Google Scholar,16Axson J.L. May N.W. Colon-Bernal I.D. Pratt K.A. Ault A.P. Lake spray aerosol: a chemical signature from individual ambient particles.Environ Sci Technol. 2016; 50: 9835-9845Crossref PubMed Scopus (29) Google Scholar or estuarine environments.17Plaas H.E. Paerl R.W. Baumann K. et al.Harmful cyanobacterial aerosolization dynamics in the airshed of a eutrophic estuary.Sci Total Environ. 2022; 852158383Crossref PubMed Scopus (4) Google Scholar SAs are formed when wind-driven wave action entrains plumes of air bubbles beneath the water followed by bubbles bursting at the air-water interface, ejecting water droplets into the atmosphere that can contain organic material from cells or whole cells themselves.18Ault A.P. Zhao D. Ebben C.J. et al.Raman microspectroscopy and vibrational sum frequency generation spectroscopy as probes of the bulk and surface compositions of size-resolved sea spray aerosol particles.Phys Chem Chem Phys. 2013; 15: 6206-6214Crossref PubMed Scopus (91) Google Scholar, 19Ault A.P. Moffet R.C. Baltrusaitis J. et al.Size-dependent changes in sea spray aerosol composition and properties with different seawater conditions.Environ Sci Technol. 2013; 47: 5603-5612Crossref PubMed Scopus (153) Google Scholar, 20Patterson J.P. Collins D.B. Michaud J.M. et al.Sea spray aerosol structure and composition using cryogenic transmission electron microscopy.ACS Cent Sci. 2016; 2: 40-47Crossref PubMed Scopus (67) Google Scholar Elevated concentrations of biomass during HAB conditions result in a greater proportion of the SA mass composed of biological material along with shifting of the size distributions.15May N.W. Olson N.E. Panas M. et al.Aerosol emissions from great lakes harmful algal blooms.Environ Sci Technol. 2018; 52: 397-405Crossref PubMed Scopus (48) Google Scholar The properties of bubbles leading to aerosolization significantly differ between marine SSA and freshwater LSA, with bubbles formed in freshwater much larger than in seawater.21Cartmill J.W. Su M.Y. Bubble size distribution under saltwater and freshwater breaking waves.Dynam Atmos Oceans. 1993; 20: 25-31Crossref Scopus (49) Google Scholar The larger bubbles, combined with different aquatic chemistry for marine and freshwater systems, lead to dramatically different aerosol concentrations, particle size distributions, and aerosol chemical composition.22May N.W. Axson J.L. Watson A. Pratt K.A. Ault A.P. Lake spray aerosol generation: a method for producing representative particles from freshwater wave breaking.Atmos Meas Tech. 2016; 9: 4311-4325Crossref Scopus (30) Google Scholar For example, ambient LSA number concentrations are about one-third that of SSA and have a chemical composition composed primarily of calcium carbonate and organic carbon. Studies on freshwater and estuarine SA generation and HAB toxin aerosolization remain relatively limited compared to marine environments. The mechanisms by which HAB toxins become incorporated into aerosols are dependent on species and environmental conditions. Brevetoxins, which are hydrophobic toxins produced by K. brevis, are mainly released into the water column through cell lysis due to physical forces, especially towards the end of the blooms.12Patel S.S. Lovko V.J. Lockey R.F. Red tide: overview and clinical manifestations.J Allergy Clin Immunol Pract. 2020; 8: 1219-1223Summary Full Text Full Text PDF PubMed Scopus (14) Google Scholar Toxins from cyanobacteria, on the other hand, are not usually released from cell lysis due to shear stress or turbulence but are released during cell senescence, exposure to heightened salinity, or from lysis from viral activity.23Plaas H.E. Paerl H.W. Toxic cyanobacteria: a growing threat to water and air quality.Environ Sci Technol. 2020; 55: 44-64Crossref PubMed Scopus (97) Google Scholar These extracellular toxins are then enriched at the air-water interface of the bubbles generated by wave action and water turbulence.12Patel S.S. Lovko V.J. Lockey R.F. Red tide: overview and clinical manifestations.J Allergy Clin Immunol Pract. 2020; 8: 1219-1223Summary Full Text Full Text PDF PubMed Scopus (14) Google Scholar Toxin concentration levels in aerosols may be significantly higher than in the water due to bubble scavenging, with one work finding that aerosols can contain levels of brevotoxin that are 20–50 times greater than in seawater,24Pierce R.H. Henry M.S. Blum P.C. et al.Brevetoxin composition in water and marine aerosol along a Florida beach: assessing potential human exposure to marine biotoxins.Harmful Algae. 2005; 4: 965-972Crossref Scopus (107) Google Scholar while another study found 78- to 1769-fold enrichment of phycotoxins in SAs.25Van Acker E. Huysman S. De Rijcke M. et al.Phycotoxin-enriched sea spray aerosols: methods, mechanisms, and human exposure.Environ Sci Technol. 2021; 55: 6184-6196Crossref PubMed Scopus (8) Google Scholar The aerosols generated from seawater and freshwater cover a wide size range important for inhalation exposure. Analyses of the particle size distribution of air samples collected during red tides showed that the generated aerosols were mainly coarse particles, which deposit mainly in the upper respiratory tract, with a small percentage (2–6%) that would travel to tracheobronchial and alveolar regions.24Pierce R.H. Henry M.S. Blum P.C. et al.Brevetoxin composition in water and marine aerosol along a Florida beach: assessing potential human exposure to marine biotoxins.Harmful Algae. 2005; 4: 965-972Crossref Scopus (107) Google Scholar,26Cheng Y.S. Zhou Y. Irvin C.M. et al.Characterization of marine aerosol for assessment of human exposure to brevetoxins.Environ Health Perspect. 2005; 113: 638-643Crossref PubMed Scopus (94) Google Scholar An analysis of aerosols and multiple HAB toxins (brevetoxin, okadaic acid, pectenotoxin-2, domoic acid, tetrodotoxin, saxitoxin, ciguatoxin, and ω-Conotoxin) off the coast of China found that the particles were predominantly coarse, and deposition efficiency was found in the head airway region (74.06%–75.76%), followed by the alveolar (16.14%–17.40%) and tracheobronchial (8.24%–8.69%) regions.27Yu S. Zhou X. Hu P. et al.Inhalable particle-bound marine biotoxins in a coastal atmosphere: concentration levels, influencing factors and health risks.J Hazard Mater. 2022; 434128925Crossref Scopus (1) Google Scholar An experimental study found that an increase in cyanoHAB activity enhanced aerosol production in the ultrafine size range (da < 100 nm) and accumulation modes (100–1000 nm),28Olson N.E. Cooke M.E. Shi J.H. Birbeck J.A. Westrick J.A. Ault A.P. Harmful algal bloom toxins in aerosol generated from inland lake water.Environ Sci Technol. 2020; 54: 4769-4780Crossref PubMed Scopus (51) Google Scholar which can penetrate deeper into the respiratory tract than fine and coarse aerosols. The size of aerosols further varies as a function of distance from HAB locations. Inland microalgae and cyanobacteria frequently occurred in particles not exceeding a diameter of 3.3 μm, while over the sea bioaerosol particles had a diameter of >3.3 μm, as smaller particles are likely to be transported further inland via wind.29Lewandowska A.U. Śliwińska-Wilczewska S. Woźniczka D. Identification of cyanobacteria and microalgae in aerosols of various sizes in the air over the Southern Baltic Sea.Mar Pollut Bull. 2017; 125: 30-38Crossref PubMed Scopus (36) Google Scholar The transport of SA in the environment is dependent primarily on the aerodynamic diameter and meteorology. Wave action can produce SSA that can be transported up to 1000 km via wind.30Bondy A.L. Wang B. Laskin A. et al.Inland sea spray aerosol transport and incomplete chloride depletion: varying degrees of reactive processing observed during SOAS.Environ Sci Technol. 2017; 51: 9533-9542Crossref PubMed Scopus (48) Google Scholar Prior measurements of LSA concentrations have observed LSA transported >30 km inland,31May N.W. Gunsch M.J. Olson N.E. et al.Unexpected contributions of sea spray and lake spray aerosol to inland particulate matter.Environ Sci Technol Lett. 2018; 5: 405-412Crossref Scopus (30) Google Scholar while modelling has shown that freshwater aerosol production contributes significantly to particle number concentrations over the Great Lakes region and significantly impacts atmospheric chemistry over the lakes.32Chung S. Basarab B. VanReken T. Regional impacts of ultrafine particle emissions from the surface of the Great Lakes.Atmos Chem Phys. 2011; 11: 12601-12615Crossref Scopus (14) Google Scholar The maximum distance travelled by aerosolized toxins could be transported depends on the stability of the compound in question under a range of environmental conditions and remains unclear due to the difficulty of measuring some toxins and scarce direct measurement data. During the Florida red tide, brevetoxins produced by Karenia brevis were detected in the aerosol samples as far as 4.2 km from the beach of origin,33Kirkpatrick B. Pierce R. Cheng Y.S. et al.Inland transport of aerosolized Florida red tide toxins.Harmful Algae. 2010; 9: 186-189Crossref PubMed Scopus (43) Google Scholar while during cyanobacteria HAB events, microcystin in atmospheric particles could be transported many kilometres inland without degradation as it is a very stable compound.23Plaas H.E. Paerl H.W. Toxic cyanobacteria: a growing threat to water and air quality.Environ Sci Technol. 2020; 55: 44-64Crossref PubMed Scopus (97) Google Scholar Bioaerosols collected over the Baltic Sea, as well as hundreds of meters inland, harboured cyanobacteria and other related microalgae species.28Olson N.E. Cooke M.E. Shi J.H. Birbeck J.A. Westrick J.A. Ault A.P. Harmful algal bloom toxins in aerosol generated from inland lake water.Environ Sci Technol. 2020; 54: 4769-4780Crossref PubMed Scopus (51) Google Scholar Multiple HAB toxins have been detected at a sampling site that was 25 km away from the coast in Qingdao, China.27Yu S. Zhou X. Hu P. et al.Inhalable particle-bound marine biotoxins in a coastal atmosphere: concentration levels, influencing factors and health risks.J Hazard Mater. 2022; 434128925Crossref Scopus (1) Google Scholar Aerosolized toxins may also persist along the shore, where blooms tend to accumulate.23Plaas H.E. Paerl H.W. Toxic cyanobacteria: a growing threat to water and air quality.Environ Sci Technol. 2020; 55: 44-64Crossref PubMed Scopus (97) Google Scholar After transport onshore by wind, aerosolized HAB toxins are deposited mostly in the upper respiratory tract. Brevetoxins were detected in the nasal-pharyngeal swabs of individuals (n = 129) exposed to red tide events.34Backer L.C. Fleming L.E. Rowan A. et al.Recreational exposure to aerosolized brevetoxins during Florida red tide events.Harmful Algae. 2003; 2: 19-28Crossref Scopus (131) Google Scholar After recreational activities in a small lake with a cyanobacterial bloom, low levels of microcystins were detected in water and air samples, but blood levels were below the level of detection (n = 97).35Backer L.C. Carmichael W. Kirkpatrick B. et al.Recreational exposure to low concentrations of microcystins during an algal bloom in a small lake.Mar Drugs. 2008; 6: 389-406Crossref PubMed Scopus (96) Google Scholar In a study of children and adults (n = 81) who had gone to two California lakes, microcystin levels before and after recreational activities were measured in plasma and nasal swab specimens, with elevated concentrations in nasal specimens but not in plasma.36Backer L.C. McNeel S.V. Barber T. et al.Recreational exposure to microcystins during algal blooms in two California lakes.Toxicon. 2010; 55: 909-921Crossref PubMed Scopus (153) Google Scholar An examination of MC levels in the nasal mucosa of participants (n = 125) during a cyanobacterial bloom of cyanobacteria Microcystis aeruginosa found that 95% had concentrations of MC above the limit of detection, with significantly elevated MC concentrations among individuals with direct contact with impacted waters compared to those with no recent contact.37Schaefer A.M. Yrastorza L. Stockley N. et al.Exposure to microcystin among coastal residents during a cyanobacteria bloom in Florida.Harmful Algae. 2020; 92101769Crossref PubMed Scopus (24) Google Scholar In this work, nasal concentrations of MC were found to vary by time and location of exposure to HAB, with the highest levels observed during periods when concentrations in the surrounding waters peaked. In contrast, there was no statistical difference in detected levels between bloom and non-bloom seasons as well as residential proximity to a body of water in a study (n = 29) in cyanotoxins levels in the upper airways and central airway were detected using PCR, suggesting that exposure could be more ubiquitous across both time and space, including locations that are not nearby waterbodies.38Facciponte D.N. Bough M.W. Seidler D. et al.Identifying aerosolized cyanobacteria in the human respiratory tract: a proposed mechanism for cyanotoxin-associated diseases.Sci Total Environ. 2018; 645: 1003-1013Crossref PubMed Scopus (31) Google Scholar The studies that have examined cyanotoxin in the blood did not detect concentrations above detectable limits,34Backer L.C. Fleming L.E. Rowan A. et al.Recreational exposure to aerosolized brevetoxins during Florida red tide events.Harmful Algae. 2003; 2: 19-28Crossref Scopus (131) Google Scholar,35Backer L.C. Carmichael W. Kirkpatrick B. et al.Recreational exposure to low concentrations of microcystins during an algal bloom in a small lake.Mar Drugs. 2008; 6: 389-406Crossref PubMed Scopus (96) Google Scholar,38Facciponte D.N. Bough M.W. Seidler D. et al.Identifying aerosolized cyanobacteria in the human respiratory tract: a proposed mechanism for cyanotoxin-associated diseases.Sci Total Environ. 2018; 645: 1003-1013Crossref PubMed Scopus (31) Google Scholar suggesting that the toxins may not cross the blood-air barrier or that the HAB toxins may transform into other metabolites that have not been identified thus far.23Plaas H.E. Paerl H.W. Toxic cyanobacteria: a growing threat to water and air quality.Environ Sci Technol. 2020; 55: 44-64Crossref PubMed Scopus (97) Google Scholar Intergovernmental Panel on Climate Change's (IPCC) Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) in 2019 directly linked HABs to climate change, stating with high confidence that “harmful algal blooms display range expansion and increased frequency in coastal areas since the 1980s in response to both climatic and non-climatic drivers such as increased riverine nutrients run-off.”39Pörtner H.-O. Roberts D.C. Masson-Delmotte V. et al.The ocean and cryosphere in a changing climate.in: IPCC special report on the ocean and cryosphere in a changing climate. 2019Google Scholar However, the extent to which climate change is intensifying HABs remains unclear. Warming is linked to shifts in the composition of microorganisms and the promotion of rapidly proliferating HABs.2Gobler C.J. Doherty O.M. Hattenrath-Lehmann T.K. Griffith A.W. Kang Y. Litaker R.W. Ocean warming since 1982 has expanded the niche of toxic algal blooms in the North Atlantic and North Pacific oceans.Proc Natl Acad Sci U S A. 2017; 114: 4975-4980Crossref PubMed Scopus (269) Google Scholar Studies have shown that progressively warming waters have resulted in regions with increasing frequencies and intensities of HABs, resulting in HAB extents that may be moving towards higher latitudes.2Gobler C.J. Doherty O.M. Hattenrath-Lehmann T.K. Griffith A.W. Kang Y. Litaker R.W. Ocean warming since 1982 has expanded the niche of toxic algal blooms in the North Atlantic and North Pacific oceans.Proc Natl Acad Sci U S A. 2017; 114: 4975-4980Crossref PubMed Scopus (269) Google Scholar,4Griffith A.W. Gobler C.J. Harmful algal blooms: a climate change co-stressor in marine and freshwater ecosystems.Harmful Algae. 2020; 91101590Crossref PubMed Scopus (186) Google Scholar Acidification with increasing CO2 levels in the water may be further promoting growth rates of HABs, whereas non-harmful algae did not demonstrate this trend.40Brandenburg K.M. Velthuis M. Van de Waal D.B. Meta-analysis reveals enhanced growth of marine harmful algae from temperate regions with warming and elevated CO2 levels.Global Change Biol. 2019; 25: 2607-2618Crossref PubMed Scopus (39) Google Scholar Altered precipitation patterns and the frequency of extreme weather events are further impacting the delivery of nutrients into aquatic ecosystems.41Coffey R. Paul M.J. Stamp J. Hamilton A. Johnson T. A review of water quality responses to air temperature and precipitation changes 2: nutrients, algal blooms, sediment, pathogens.J Am Water Resour Assoc. 2019; 55: 844-868Crossref Scopus (31) Google Scholar Accelerating eutrophication can lead to algal blooms and subsequent loss of dissolved oxygen, furthering a change in ecosystem states that pose major threats to both aquatic ecosystems and human health. While regional analyses have reported increasing trends, the global trends are less clear. Analysis of the recent 30-year (1990–2019) database from the Harmful Algae Event Database and Ocean Biodiversity Information System (HAEDAT) shows an increasing trend in all HAB events.1Anderson D.M. Fensin E. Gobler C.J. et al.Marine harmful algal blooms (HABs) in the United States: history, current status and future trends.Harmful Algae. 2021; 102101975Crossref PubMed Scopus (103) Google Scholar However, these trends are not uniformly consistent across regions and may be due in part to increased awareness, monitoring, and reporting.42Hallegraeff G.M. Anderson D.M. Belin C. et al.Perceived global increase in algal blooms is attributable to intensified monitoring and emerging bloom impacts.Commun Earth Environ. 2021; 2: 117Crossref Scopus (131) Google Scholar Freshwater HABs and their toxins are transported along a connected network of estuarine and coastal water sources, requiring multiregional assessments and solutions.43Zepernick B.N. Wilhelm S.W. Bullerjahn G.S. Paerl H.W. Climate change and the aquatic continuum: a cyanobacterial comeback story.Environ Microbiol Rep. 2023; 15: 3-12Crossref PubMed Scopus (5) Google Scholar Predicting how HABs will respond to climate change is challenging as this will vary significantly across species, interactive effects of stressors that impact growth, and adaptation. The effects of warming and acidification on toxin production are also unclear, with species-specific responses reported.44Raven J.A. Gobler C.J. Hansen P.J. Dynamic CO2 and pH levels in coastal, estuarine, and inland waters: theoretical and observed effects on harmful algal blooms.Harmful Algae. 2020; 91101594Crossref PubMed Scopus (64) Google Scholar Studies may disagree on the magnitude or even the direction of the growth rate response of HAB genera to climate change perturbations such as CO2.45Wells M.L. Trainer V.L. Smayda T.J. et al.Harmful algal blooms and climate change: learning from the past and present to forecast the future.Harmful Algae. 2015; 49: 68-93Crossref PubMed Scopus (443) Google Scholar Overall, the effects of climate change on toxin production – and thus the associated health impacts-remain uncertain, as the relationship between temperature and HAB toxicity is complex and highly dependent on a variety of contributing factors including nutrient and light status as well as species composition, which may further differ geographically. Direct sampling of waters via vessels and collecting samples from buoys and moored automated collection devices are the most common and traditional approaches for assessing HAB composition and size.46Glibert P.M. Pitcher G.C. Bernard S. Li M. Advancements and continuing challenges of emerging technologies and tools for detecting harmful algal blooms, their antecedent conditions and toxins, and applications in predictive models.in: Global ecology and oceanography of harmful algal blooms. 2018: 339-357Crossref Google Scholar Within the collected samples,

Full Text

Published Version
Open DOI Link

Get access to 115M+ research papers

Discover from 40M+ Open access, 2M+ Pre-prints, 9.5M Topics and 32K+ Journals.

Sign Up Now! It's FREE

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call