Difference between revisions of "Harmful algal bloom"

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{{Definition|title= Harmful Algal Bloom (HAB)
 
{{Definition|title= Harmful Algal Bloom (HAB)
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|definition= Harmful algal blooms or HABs are [[algal bloom]]s composed of phytoplankton known to naturally produce biotoxins, they can occur when certain types of microscopic algae grow quickly in water, forming visible patches that may harm the health of the environment, plants, or animals. HABs can deplete the oxygen and block the sunlight that other organisms need to live, and some HAB-causing algae release toxins that are dangerous to animals and humans. HAB can occur in marine, estuarine, and fresh waters.
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|definition= Harmful algal blooms or HABs are [[algal bloom]]s composed of phytoplankton that naturally produce biotoxins. Harmful algal blooms (HABs) can occur in marine, estuarine, and fresh waters.<br>
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}}
 
  
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==Notes==  
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The term 'harmful algal bloom' is sometimes used to designate any phytoplankton bloom event that causes 'negative' impacts on the marine ecosystem, for example oxygen depletion or sunlight shading. }}
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The frequency and intensity of recorded harmful algal blooms has increased worldwide over the past decades. The reason for this is often assumed to be [[eutrophication]]. However, many other explanations are possible, for example increased transport of algae with ship ballast water or increased monitoring efforts. For management purposes it is important to understand which are the main factors controlling the risk of harmful algal blooms. For a long time, a link was made between high nutrient concentrations and harmful algal blooms. More recently, researchers point out the importance of interacting biological and physical processes, including effects of wind, currents and water temperature.
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This article deals with toxic algal blooms: effects, environmental conditions, factors that promote HABs and management measures.
 +
 
 +
 
 +
==Effects of harmful algal blooms==
 +
 
 +
The toxins produced by harmful algal blooms (HABs) have direct negative impacts on human health and on many marine organisms. Marine HABs further impact on other aspects of human wellbeing, including human commercial and recreational uses of the coastal and marine environments, such as fishing, aquaculture and tourism, and non-market, passive uses of the ocean, such as preferences for particular ecological states.
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 +
Most algal toxins are neurotoxins, which can affect the nervous, digestive, respiratory, hepatic, dermatological or cardiac systems. Consumption of toxins bio-accumulated in shellfish produces shellfish poisoning (PS) syndromes such as <ref name=Ber16>Berdalet, E., Fleming, L.E., Gowen, R., Davidson, K., Hess, P., Backer, L.C., Moore, S.K., Hoagland, P. and Enevoldsen, H. 2016. Marine harmful algal blooms, human health and wellbeing: challenges and opportunities in the 21st century. J. Mar. Biol. Assoc. U.K. 96: 61–91</ref>
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[https://en.wikipedia.org/wiki/Amnesic_shellfish_poisoning Amnesic SP],  [https://en.wikipedia.org/wiki/Azaspiracid Azaspirazid SP], [https://en.wikipedia.org/wiki/Diarrhetic_shellfish_poisoning Diarrhetic SP], [https://en.wikipedia.org/wiki/Neurotoxic_shellfish_poisoning Neurotoxic SP] and [https://en.wikipedia.org/wiki/Paralytic_shellfish_poisoning Paralytic SP]. Toxins in fish can produce [https://en.wikipedia.org/wiki/Ciguatera_fish_poisoning Ciguatera Fish Poisoning].
 +
 
 +
Beach visitors can experience serious health problems when respiring aerosols containing algal biotoxins<ref>Fleming L.E., Kirkpatrick B., Backer L.C., Walsh C.J., Nierenberg K., Clark J., Reich A., Hollenbeck J., Benson J., Cheng Y.S., Naar J., Pierce R., Bourdelais A.J., Abraham W.M., Kirkpatrick G., Zaias J., Wanner A., Mendes E., Shalat S., Hoagland P., Stephan W., Bean J., Watkins S., Clarke T., Byrne M. and Baden D.G. 2011. Review of Florida red tide and human health effects. Harmful Algae 20: 224–233</ref><ref>Berdalet E., Vila M. and Abos-Herrandiz, R. 2015. Expansion of the benthic dinoflagellate Ostreopsis with climate change: health risks assessment and policy strategies for management. Harmful Algal Blooms and Climate Change Scientific Symposium. Goteborg, Sweden, 19–22 May 2015</ref>.
 +
Toxic HABs have recently emerged as a potential risk for the contamination of drinking water supplied by desalination systems<ref>Seubert, E.L., Trussell, S., Eagleton, J., Schnetzer, A., Cetinic, I., Lauri, P., Jones, B.H. and Caron, D.A. 2012. Algal toxins and reverse osmosis desalination operations: laboratory bench testing and field monitoring of domoic acid, saxitoxin, brevetoxin and okadaic acid. Water Research 46: 6563–6573</ref><ref>Berman, T. 2013. Transparent exopolymer particles as critical agents in aquatic biofilm formation: implications for desalination and water treatment, Desalination and Water Treatment 51: 4-6</ref><ref>Flemming, H.C. and Wingender, J. 2001. Relevance of microbial extracellular polymeric substances (EPSs)--Part I: Structural and ecological aspects. Water Sci Technol. 43(6): 1-8</ref>.
 +
 
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Socio-economic costs cannot easily be quantified, but they are considerable<ref name=Ber16/> . 
 +
Estimates are in the order of US$100 million per year in the United States, mainly related to aquaculture losses. A much higher estimate of about US $ 1 billion per year was estimated for Europe, mainly due to losses related to (not necessarily toxic) algal blooms affecting the attractiveness of beaches for coastal tourists<ref>Hoagland P. and Scatasta S. (2006) The economic effects of harmful algal blooms. In Graneli E. and Turner J.T. (eds) Ecology of harmful algae. New York, NY: Springer-Verlag, pp. 391–402</ref>.
 +
 
 +
The greatest direct effect of HABs concerns aquaculture. Aquaculture has experienced tremendous growth in recent decades and has become a food source on which much of the world's population depends. As the growth of aquaculture is expected to continue, harmful algal blooms are an increasing threat. The paradox is that the waste from fish and shellfish farms itself promotes conditions for the development of HABs<ref>Anderson, D. 2012. HABs in a changing world: a perspective on harmful algal blooms, their impacts, and research and management in a dynamic era of climactic and environmental change. Harmful Algae 2012 (2012). 2014 ; 2012: 3–17 PMID: 26640829; PMCID: PMC4667985</ref>.
 +
 
 +
 
 +
==Conditions favouring the development of harmful algal blooms==
 +
 
 +
HABs are natural phenomena, but these events can be favoured by anthropogenic pressures in coastal areas. It is not known exactly how toxin producing algae develop. What is known, however, is that most toxic algae belong to the class of flagellates and cyanobacteria. Environmental conditions favorable for the development of flagellates and cyanobacteria therefore create the greatest risk for the development of HABs. Among the algae of the diatom class there are also toxic species, but these are rarer than among the flagellates. The following is known about the shift from conditions favorable for the development of diatoms to conditions favorable for the development of flagellates and cyanobacteria:
 +
 
 +
# Higher temperatures. The optimal growth of diatoms occurs at relatively low temperatures compared to flagellates and cyanobacteria<ref>Anderson, N.J. 2000. Diatoms, temperature and climate change. Eur. J. Phycol. 35: 307–314</ref>. Experiments show that the occurrence of HABs increases with temperature<ref>Paerl, H.W. and Scott, J.T. 2010. Throwing fuel on the fire: synergistic effects of excessive nitrogen inputs and global warming on harmful algal blooms. Environ. Sci. Technol. 44: 7756–7758</ref>. Warmer waters are thought to favor smaller-sized cells as they are more efficient in harvesting light and nutrients and maintaining their position in the euphotic zone<ref>Daufresne, M., Lengefellner, K. and Sommer, U. 2009. Global warming benefits the small in
 +
aquatic ecosystems. Proc. Natl. Acad. Sci. U. S. A. 106: 12788–12793<ref>. Cyanobacteria dominate in warm nutrient-poor water <ref>Maranon, E., Cermeno, P., Latasa, M. and Tadonleke, R.D. 2012. Temperature, resources, and phytoplankton size structure in the ocean. Limnol. Oceanogr. 67: 1266–1278</ref>.
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# A high ratio of dissolved nitrogen N versus phosphorus P. This has several causes: (a) Very small cells, such as picocyanobacteria, have a lower requirement for P due to the smaller need for structural components in the cell<ref>Finkel, Z.V., J. Beardall, K.J. Flynn, A. Quiqq, T.A.V. Rees, and J.A. Raven. 2010. Phytoplankton in a changing world: Cell size and elemental stoichiometry. Journal of Plankton Research 32:119–137</ref>; (b) Many dinoflagellates are mixotrophic <ref>Mitra, A. and Flynn, K.J. 2010. Modelling mixotrophy in harmful algal blooms: more or less the sum of the parts? J. Mar. Syst. 83: 58–169</ref><ref>Stoecker, D., Tillmann, U. and Graneli, E. 2006. Phagotrophy in harmful algae. In: Graneli, E. and Turner, J. (eds) Ecology of Harmful Algae, Series: Ecological Studies, Vol. 189, Springer Verlag, Heidelberg, pp 177–187</ref>, which means that they can ingest organic material and thus correct an imbalance in the  [[Stoichiometry|stoichiometric]] N:P ratio<ref>Burkholder, J.M., Glibert, P.M. and Skelton, H. 2008. Mixotrophy, a major mode of nutrition for harmful algal species in eutrophic waters. Harmful Algae 8: 77–93</ref><ref>Jeong, H.J., Yoo, Y.D., Kim, J.S., Seong, K.A., Kang, N.S. and Kim, T.H., 2010. Growth, feeding and ecological roles of the mixotrophic and heterotrophic dinoflagellates in marine planktonic food webs. Ocean Sci. J. 45: 65–91</ref><ref>Flynn, K.J., Stoecker, D.K., Mitra, A., Raven, J.A., Glibert, P.M., Hansen, P.J., Graneli, E. and Burkholder, J.M. 2013. Misuse of the phytoplankton-zooplankton dichotomy: the need to assign organisms as mixotrophs within plankton functional types. J. Plankt. Res 35: 3–11</ref>; (c) Harmful algae can release excess N via toxins <ref name=G16>Glibert, P.M., Wilkerson, F.P., Dugdale, R.C., Raven, J.A., Dupont, C., Leavitt, P.R., Parker, A.E., Burkholder, J.M. and Kana, T.M. 2016. Pluses and minuses of ammonium and nitrate uptake and assimilation by phytoplankton and implications for productivity and community composition, with emphasis on nitrogen-enriched conditions. Limnol. Oceanogr. 61: 165–197</ref>. Many cyanobacteria and marine dinoflagellate HABs are more toxic when N is in stoichiometric excess over P. In the dinoflagellate ''Alexandrium tamarense'', saxitoxin production has been shown to increase by three- to fourfold under P deficiency<ref>Graneli, E., and Flynn, K.J. 2006. Chemical and physical factors influencing toxin content. Pp. 229–241 in Ecology of Harmful Algae. E. Graneli, and J.T. Turner, eds, Springer, Heidelberg, Germany</ref>.
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# Increasing proportions of N in the form of ammonium and urea (CO(NH<sub>2</sub>)<sub>2</sub>). Causes: (a) Diatoms grow better on nitrate (NO<sub>3</sub><sup>-</sup>) whereas flagellates and cyanobacteria prefer ammonium (NH<sub>4</sub><sup>+</sup>) <ref name=G17>Glibert, P.M. 2017. Eutrophication, harmful algae and biodiversity - challenging paradigms in a world of complex nutrient changes. Mar. Poll. Bull. 124: 591–606</ref>; (b) Mixotrophic dinoflagellates can use urea as food source<ref name=G14>Glibert, P.M., Manager, R., Sobota, D.J., Bouwman, L. 2014. The Haber-Bosch-Harmful algal bloom (HB-HAB) link. Environ. Res. Lett. 9, 105001</ref>.
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# Enhancement of stratified conditions. Causes are: (a) Larger phytoplankton sinks more easily out of the photic zone, thus smaller plankton dominates <ref>Winder, M., Reuter, J.E. and Schladow, S.G. 2009. Lake warming favours small-sized plankton diatom species. Proc. Roy. Soc B 276: 427–435</ref>; (b) Many harmful dinoflagellates are mixotrophs which can swim to the pycnocline to capture organic prey<ref>Stoecker, D.K., Hansen, P.J., Caron, D.A. and Mitra, A. 2017. Mixotrophy in the marine plankton. Ann. Rev. Mar. Sci. 9: 311–335</ref>.
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# Retention of Si in reservoirs behind river dams. Diatoms require Si for growth; Si limitation favours non-Si species such as flagellates and cyanobacteria<ref>Maavara, T., Dürr, H.H. and Van Cappellen, P. 2014. Worldwide retention of nutrient silicon by river damming: from sparse data set to global estimate. Glob. Biogeochem. Cycl. 28: 842–855</ref><ref>Maavara, T., Parsons, C.T., Ridenour, C., Stojanovic, S., Dürr, H.H., Powley, H.R. and Van Cappellen, P. 2015. Global phosphorus retention by river damming. Proc. Natl. Acad. Sci. U. S. A. 112, 15603–15608</ref>.
 +
 
 +
 
 +
==Causes for an increase in HABs==
 +
 
 +
Although no quantitative estimates can be given, there is strong evidence that the occurrence of harmful algal blooms has increased during the past decades. The causes for an increase in HABs are related to the furtherance of the above mentioned conditions favorable for their development. Probable causes are:
 +
 
 +
# Increase of nitrogen-rich effluents and atmospheric emissions to the sea. The main cause is the increasing use of fertilizers, which contain a much higher proportion of nitrogen than phosphorus (about a factor of 3, see Fig. 1)<ref name=GB>Glibert, P.M. and Burford, M.A. 2017. Globally changing nutrient loads and harmful algal blooms: Recent advances, new paradigms, and continuing challenges. Oceanography 30: 58–69</ref>. Only about half of the fertilizer nutrients used in agriculture is taken up by crops; the remainder is stored in the soil and released to the sea. Other N-rich sources are the widespread and expanding fish and shellfish farms, that release N mainly in chemically reduced form (e.g., ammonium, dissolved organic N, DON)<ref>Bouwman, A.F., Beusen, A.H.W., Glibert, P.M., Overbeck, C., Pawlowski, M., Silveiva, J.H., Mulsow, S., Yu, R. and Zhou, M.J. 2013. Mariculture: significant and expanding cause of coastal nutrient enrichment. Environ. Res. Lett. 8, 044026</ref>.
 +
# Fertilizer effluents and emissions produce a shift from nitrate to ammonium and urea that favours HABs<ref name=G16/><ref name=G14/>.
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# Effects of climate change: (a) Rising seawater temperatures; (b) Intensification of sea water stratification; (c) Increase in peak river discharges and corresponding increase in nitrogen supply in coastal waters<ref>Howarth, R.W., Swaney, D.P., Boyer, E.W., Marino, R., Jaworski, N. and Goodale, C. 2006. The influence of climate on average nitrogen export from large watersheds in the Northeastern United States. Biogeochemistry 79: 163–186</ref>; (d) Increase in nutrient concentrations associated with intensification upwelling events<ref>Goes, J.I., Thoppil, P.G., Gomes, H.D.R. and Fasullo, J.T. 2005. Warming of the Eurasian landmass is making the Arabian Sea more productive. Science 308: 545–547</ref>.
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# Spreading of harmful algae species across the oceans by increased transport of algae with ship ballast water<ref name=Ber16/>.
 +
 
 +
 
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[[File:NPfertlizerUse.jpg|thumb|600px|center|Fig. 1. N and P content of global fertilizer use. From Glibert and Burford, 2017<ref name=GB/>]]
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 +
 
 +
==Measures for reducing the risk of HABs==
 +
 
 +
The factors that promote the occurrence of HABs are expected to become more important in the future. This holds in the first place for global warming and for eutrophication, in particular the nitrogen component of eutrophication. Efforts to combat harmful algal blooms are vital, but simple solutions do not exist. It is widely recognized that action is needed to halt global climate change and to reduce nitrogen emissions from agriculture. To this end, agreements have been made and initiatives have been developed at various administrative levels. Important international frameworks have been set up for climate policy that will eventually reverse the trend of global warming. A comparable encompassing agreement has not yet been established for agricultural emissions, although in Europe the [[Nitrates Directive]] has been in force since 1991. This directive has contributed to a reduction in N emissions from European agriculture<ref>Velthof G.L., Lesschen, J.P., Webb, J., Pietrzak, S., Miatkowski, Z., Pinto, M., Kros, J. and Oenema, O. 2014.The impact of the Nitrates Directive on nitrogen emissions from agriculture in the EU-27during 2000–2008. Science of theTotal Environment 468–469: 1225–1233</ref> - however, without special focus on the nitrate: ammonium ratio of the emissions.
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Other measures may also contribute to mitigate the impact of HABs. Some important elements of HAB measures are mentioned below (for a more detailed and complete overview see e.g. Berdalet et al., 2016<ref name=Ber16/> and Wells et al., 2020<ref> Wells, M.L., Karlson, B., Wulff, A., Kudela, R., Trick, C., Asnaghi, V., Berdalet, E., Cochlan, W.,. Davidson, K., De Rijcke, M., Dutkiewicz, S., Hallegraeff, G., Flynn, K.J., Legrand, C., Paerl, H., Slke, J., Suikkanen, S., Thompson, P. and Trainer, V.L. 2020. Future HAB science: Directions and challenges in a changing climate. Harmful Algae 91, 101632</ref>):
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*Development and implementation of new efficient techniques for monitoring HABs and biotoxins and for monitoring marine conditions that are favorable for the development of HABs, in order to improve early warning;
 +
*Management measures for fish and shellfish farms to reduce the release of nutrient-rich waste, for example by installing water treatment and flushing systems;
 +
*Relocation of aquaculture farms to offshore areas where excess N concentrations are less likely to build up;
 +
*Furthering understanding of fundamental aspects of HAB species in terms of toxin production, life cycles and interactions with bacteria in order to develop better targeted measures.
 +
 
 +
Measures to eliminate harmful algae, for example through the use of viruses, grazers or biocides, encounter serious problems due to hazardous side effects. That is why many countries have bans on such measures. Experiments in Korea to remove toxic algae through flocculation using clay particles have reported successful application without harmful side effects<ref>Yu, Z.M., Song, X.X., Cao, X.H. and Liu, Y., 2017. Mitigation of harmful algal blooms using modified clays: theory, mechanisms, and applications. Harmful Algae 69: 48–64</ref>.
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Another, more holistic approach to toxic HAB mitigation, is the restoration of coastal habitats experimented in Puget Sound, USA, with seagrass that harbor algicidal bacteria<ref>Inaba, N., Trainer, V.L., Onishi, Y., Ishii, K., Wyllie-Echeverria, S., Imai, I.and 2017. Algicidal and growth-inhibiting bacteria associated with seagrass and macroalgae beds in Puget Sounds, WA, USA. Harmful Algae 62: 136–147</ref><ref>Inaba, N., Trainer, V.L., Nagain, S., Kojima, S., Sakami, T., Takagi, S. and Imai, I. 2019. Dynamics of seagrass bed microbial communities used to control artificial Chattonella blooms: a microcosm study. Harmful Algae 84: 139–150</ref>; this can be a promising type of measures. 
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==Useful links==
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[http://www.globalhab.info/ Global Harmful Algal Blooms]
  
 
==Related articles==
 
==Related articles==
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* [[Real-time algae monitoring]]
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* [[Possible consequences of eutrophication]]
 
* [[ALGADEC - Detection of toxic algae with a semi-automated nucleic acid biosensor]]
 
* [[ALGADEC - Detection of toxic algae with a semi-automated nucleic acid biosensor]]
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* [[Algal bloom dynamics]]
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* [[Algal bloom]]
 
* [[Eutrophication in coastal environments]]
 
* [[Eutrophication in coastal environments]]
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* [[Algal bloom]]
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* [[Real-time algae monitoring]]
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* [[Algal bloom dynamics]]
 
 
* [[The Ocean as an economic area - a competitive Europe]]
 
* [[The Ocean as an economic area - a competitive Europe]]
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==References==
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<references/>
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{{author
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|AuthorID=120
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|AuthorFullName=Job Dronkers
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|AuthorName=Dronkers J}}
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[[Category:Eutrophication]]

Revision as of 21:15, 9 November 2020

Definition of Harmful Algal Bloom (HAB):
Harmful algal blooms or HABs are algal blooms composed of phytoplankton that naturally produce biotoxins. Harmful algal blooms (HABs) can occur in marine, estuarine, and fresh waters.
The term 'harmful algal bloom' is sometimes used to designate any phytoplankton bloom event that causes 'negative' impacts on the marine ecosystem, for example oxygen depletion or sunlight shading.
This is the common definition for Harmful Algal Bloom (HAB), other definitions can be discussed in the article


This article deals with toxic algal blooms: effects, environmental conditions, factors that promote HABs and management measures.


Effects of harmful algal blooms

The toxins produced by harmful algal blooms (HABs) have direct negative impacts on human health and on many marine organisms. Marine HABs further impact on other aspects of human wellbeing, including human commercial and recreational uses of the coastal and marine environments, such as fishing, aquaculture and tourism, and non-market, passive uses of the ocean, such as preferences for particular ecological states.

Most algal toxins are neurotoxins, which can affect the nervous, digestive, respiratory, hepatic, dermatological or cardiac systems. Consumption of toxins bio-accumulated in shellfish produces shellfish poisoning (PS) syndromes such as [1] Amnesic SP, Azaspirazid SP, Diarrhetic SP, Neurotoxic SP and Paralytic SP. Toxins in fish can produce Ciguatera Fish Poisoning.

Beach visitors can experience serious health problems when respiring aerosols containing algal biotoxins[2][3]. Toxic HABs have recently emerged as a potential risk for the contamination of drinking water supplied by desalination systems[4][5][6].


Socio-economic costs cannot easily be quantified, but they are considerable[1] . Estimates are in the order of US$100 million per year in the United States, mainly related to aquaculture losses. A much higher estimate of about US $ 1 billion per year was estimated for Europe, mainly due to losses related to (not necessarily toxic) algal blooms affecting the attractiveness of beaches for coastal tourists[7].

The greatest direct effect of HABs concerns aquaculture. Aquaculture has experienced tremendous growth in recent decades and has become a food source on which much of the world's population depends. As the growth of aquaculture is expected to continue, harmful algal blooms are an increasing threat. The paradox is that the waste from fish and shellfish farms itself promotes conditions for the development of HABs[8].


Conditions favouring the development of harmful algal blooms

HABs are natural phenomena, but these events can be favoured by anthropogenic pressures in coastal areas. It is not known exactly how toxin producing algae develop. What is known, however, is that most toxic algae belong to the class of flagellates and cyanobacteria. Environmental conditions favorable for the development of flagellates and cyanobacteria therefore create the greatest risk for the development of HABs. Among the algae of the diatom class there are also toxic species, but these are rarer than among the flagellates. The following is known about the shift from conditions favorable for the development of diatoms to conditions favorable for the development of flagellates and cyanobacteria:

  1. Higher temperatures. The optimal growth of diatoms occurs at relatively low temperatures compared to flagellates and cyanobacteria[9]. Experiments show that the occurrence of HABs increases with temperature[10]. Warmer waters are thought to favor smaller-sized cells as they are more efficient in harvesting light and nutrients and maintaining their position in the euphotic zoneCite error: Closing </ref> missing for <ref> tag.
  2. A high ratio of dissolved nitrogen N versus phosphorus P. This has several causes: (a) Very small cells, such as picocyanobacteria, have a lower requirement for P due to the smaller need for structural components in the cell[11]; (b) Many dinoflagellates are mixotrophic [12][13], which means that they can ingest organic material and thus correct an imbalance in the stoichiometric N:P ratio[14][15][16]; (c) Harmful algae can release excess N via toxins [17]. Many cyanobacteria and marine dinoflagellate HABs are more toxic when N is in stoichiometric excess over P. In the dinoflagellate Alexandrium tamarense, saxitoxin production has been shown to increase by three- to fourfold under P deficiency[18].
  3. Increasing proportions of N in the form of ammonium and urea (CO(NH2)2). Causes: (a) Diatoms grow better on nitrate (NO3-) whereas flagellates and cyanobacteria prefer ammonium (NH4+) [19]; (b) Mixotrophic dinoflagellates can use urea as food source[20].
  4. Enhancement of stratified conditions. Causes are: (a) Larger phytoplankton sinks more easily out of the photic zone, thus smaller plankton dominates [21]; (b) Many harmful dinoflagellates are mixotrophs which can swim to the pycnocline to capture organic prey[22].
  5. Retention of Si in reservoirs behind river dams. Diatoms require Si for growth; Si limitation favours non-Si species such as flagellates and cyanobacteria[23][24].


Causes for an increase in HABs

Although no quantitative estimates can be given, there is strong evidence that the occurrence of harmful algal blooms has increased during the past decades. The causes for an increase in HABs are related to the furtherance of the above mentioned conditions favorable for their development. Probable causes are:

  1. Increase of nitrogen-rich effluents and atmospheric emissions to the sea. The main cause is the increasing use of fertilizers, which contain a much higher proportion of nitrogen than phosphorus (about a factor of 3, see Fig. 1)[25]. Only about half of the fertilizer nutrients used in agriculture is taken up by crops; the remainder is stored in the soil and released to the sea. Other N-rich sources are the widespread and expanding fish and shellfish farms, that release N mainly in chemically reduced form (e.g., ammonium, dissolved organic N, DON)[26].
  2. Fertilizer effluents and emissions produce a shift from nitrate to ammonium and urea that favours HABs[17][20].
  3. Effects of climate change: (a) Rising seawater temperatures; (b) Intensification of sea water stratification; (c) Increase in peak river discharges and corresponding increase in nitrogen supply in coastal waters[27]; (d) Increase in nutrient concentrations associated with intensification upwelling events[28].
  4. Spreading of harmful algae species across the oceans by increased transport of algae with ship ballast water[1].


File:NPfertlizerUse.jpg
Fig. 1. N and P content of global fertilizer use. From Glibert and Burford, 2017[25]


Measures for reducing the risk of HABs

The factors that promote the occurrence of HABs are expected to become more important in the future. This holds in the first place for global warming and for eutrophication, in particular the nitrogen component of eutrophication. Efforts to combat harmful algal blooms are vital, but simple solutions do not exist. It is widely recognized that action is needed to halt global climate change and to reduce nitrogen emissions from agriculture. To this end, agreements have been made and initiatives have been developed at various administrative levels. Important international frameworks have been set up for climate policy that will eventually reverse the trend of global warming. A comparable encompassing agreement has not yet been established for agricultural emissions, although in Europe the Nitrates Directive has been in force since 1991. This directive has contributed to a reduction in N emissions from European agriculture[29] - however, without special focus on the nitrate: ammonium ratio of the emissions. Other measures may also contribute to mitigate the impact of HABs. Some important elements of HAB measures are mentioned below (for a more detailed and complete overview see e.g. Berdalet et al., 2016[1] and Wells et al., 2020[30]):

  • Development and implementation of new efficient techniques for monitoring HABs and biotoxins and for monitoring marine conditions that are favorable for the development of HABs, in order to improve early warning;
  • Management measures for fish and shellfish farms to reduce the release of nutrient-rich waste, for example by installing water treatment and flushing systems;
  • Relocation of aquaculture farms to offshore areas where excess N concentrations are less likely to build up;
  • Furthering understanding of fundamental aspects of HAB species in terms of toxin production, life cycles and interactions with bacteria in order to develop better targeted measures.

Measures to eliminate harmful algae, for example through the use of viruses, grazers or biocides, encounter serious problems due to hazardous side effects. That is why many countries have bans on such measures. Experiments in Korea to remove toxic algae through flocculation using clay particles have reported successful application without harmful side effects[31]. Another, more holistic approach to toxic HAB mitigation, is the restoration of coastal habitats experimented in Puget Sound, USA, with seagrass that harbor algicidal bacteria[32][33]; this can be a promising type of measures.


Useful links

Global Harmful Algal Blooms

Related articles


References

  1. ↑ 1.0 1.1 1.2 1.3 Berdalet, E., Fleming, L.E., Gowen, R., Davidson, K., Hess, P., Backer, L.C., Moore, S.K., Hoagland, P. and Enevoldsen, H. 2016. Marine harmful algal blooms, human health and wellbeing: challenges and opportunities in the 21st century. J. Mar. Biol. Assoc. U.K. 96: 61–91
  2. ↑ Fleming L.E., Kirkpatrick B., Backer L.C., Walsh C.J., Nierenberg K., Clark J., Reich A., Hollenbeck J., Benson J., Cheng Y.S., Naar J., Pierce R., Bourdelais A.J., Abraham W.M., Kirkpatrick G., Zaias J., Wanner A., Mendes E., Shalat S., Hoagland P., Stephan W., Bean J., Watkins S., Clarke T., Byrne M. and Baden D.G. 2011. Review of Florida red tide and human health effects. Harmful Algae 20: 224–233
  3. ↑ Berdalet E., Vila M. and Abos-Herrandiz, R. 2015. Expansion of the benthic dinoflagellate Ostreopsis with climate change: health risks assessment and policy strategies for management. Harmful Algal Blooms and Climate Change Scientific Symposium. Goteborg, Sweden, 19–22 May 2015
  4. ↑ Seubert, E.L., Trussell, S., Eagleton, J., Schnetzer, A., Cetinic, I., Lauri, P., Jones, B.H. and Caron, D.A. 2012. Algal toxins and reverse osmosis desalination operations: laboratory bench testing and field monitoring of domoic acid, saxitoxin, brevetoxin and okadaic acid. Water Research 46: 6563–6573
  5. ↑ Berman, T. 2013. Transparent exopolymer particles as critical agents in aquatic biofilm formation: implications for desalination and water treatment, Desalination and Water Treatment 51: 4-6
  6. ↑ Flemming, H.C. and Wingender, J. 2001. Relevance of microbial extracellular polymeric substances (EPSs)--Part I: Structural and ecological aspects. Water Sci Technol. 43(6): 1-8
  7. ↑ Hoagland P. and Scatasta S. (2006) The economic effects of harmful algal blooms. In Graneli E. and Turner J.T. (eds) Ecology of harmful algae. New York, NY: Springer-Verlag, pp. 391–402
  8. ↑ Anderson, D. 2012. HABs in a changing world: a perspective on harmful algal blooms, their impacts, and research and management in a dynamic era of climactic and environmental change. Harmful Algae 2012 (2012). 2014 ; 2012: 3–17 PMID: 26640829; PMCID: PMC4667985
  9. ↑ Anderson, N.J. 2000. Diatoms, temperature and climate change. Eur. J. Phycol. 35: 307–314
  10. ↑ Paerl, H.W. and Scott, J.T. 2010. Throwing fuel on the fire: synergistic effects of excessive nitrogen inputs and global warming on harmful algal blooms. Environ. Sci. Technol. 44: 7756–7758
  11. ↑ Finkel, Z.V., J. Beardall, K.J. Flynn, A. Quiqq, T.A.V. Rees, and J.A. Raven. 2010. Phytoplankton in a changing world: Cell size and elemental stoichiometry. Journal of Plankton Research 32:119–137
  12. ↑ Mitra, A. and Flynn, K.J. 2010. Modelling mixotrophy in harmful algal blooms: more or less the sum of the parts? J. Mar. Syst. 83: 58–169
  13. ↑ Stoecker, D., Tillmann, U. and Graneli, E. 2006. Phagotrophy in harmful algae. In: Graneli, E. and Turner, J. (eds) Ecology of Harmful Algae, Series: Ecological Studies, Vol. 189, Springer Verlag, Heidelberg, pp 177–187
  14. ↑ Burkholder, J.M., Glibert, P.M. and Skelton, H. 2008. Mixotrophy, a major mode of nutrition for harmful algal species in eutrophic waters. Harmful Algae 8: 77–93
  15. ↑ Jeong, H.J., Yoo, Y.D., Kim, J.S., Seong, K.A., Kang, N.S. and Kim, T.H., 2010. Growth, feeding and ecological roles of the mixotrophic and heterotrophic dinoflagellates in marine planktonic food webs. Ocean Sci. J. 45: 65–91
  16. ↑ Flynn, K.J., Stoecker, D.K., Mitra, A., Raven, J.A., Glibert, P.M., Hansen, P.J., Graneli, E. and Burkholder, J.M. 2013. Misuse of the phytoplankton-zooplankton dichotomy: the need to assign organisms as mixotrophs within plankton functional types. J. Plankt. Res 35: 3–11
  17. ↑ 17.0 17.1 Glibert, P.M., Wilkerson, F.P., Dugdale, R.C., Raven, J.A., Dupont, C., Leavitt, P.R., Parker, A.E., Burkholder, J.M. and Kana, T.M. 2016. Pluses and minuses of ammonium and nitrate uptake and assimilation by phytoplankton and implications for productivity and community composition, with emphasis on nitrogen-enriched conditions. Limnol. Oceanogr. 61: 165–197
  18. ↑ Graneli, E., and Flynn, K.J. 2006. Chemical and physical factors influencing toxin content. Pp. 229–241 in Ecology of Harmful Algae. E. Graneli, and J.T. Turner, eds, Springer, Heidelberg, Germany
  19. ↑ Glibert, P.M. 2017. Eutrophication, harmful algae and biodiversity - challenging paradigms in a world of complex nutrient changes. Mar. Poll. Bull. 124: 591–606
  20. ↑ 20.0 20.1 Glibert, P.M., Manager, R., Sobota, D.J., Bouwman, L. 2014. The Haber-Bosch-Harmful algal bloom (HB-HAB) link. Environ. Res. Lett. 9, 105001
  21. ↑ Winder, M., Reuter, J.E. and Schladow, S.G. 2009. Lake warming favours small-sized plankton diatom species. Proc. Roy. Soc B 276: 427–435
  22. ↑ Stoecker, D.K., Hansen, P.J., Caron, D.A. and Mitra, A. 2017. Mixotrophy in the marine plankton. Ann. Rev. Mar. Sci. 9: 311–335
  23. ↑ Maavara, T., Dürr, H.H. and Van Cappellen, P. 2014. Worldwide retention of nutrient silicon by river damming: from sparse data set to global estimate. Glob. Biogeochem. Cycl. 28: 842–855
  24. ↑ Maavara, T., Parsons, C.T., Ridenour, C., Stojanovic, S., Dürr, H.H., Powley, H.R. and Van Cappellen, P. 2015. Global phosphorus retention by river damming. Proc. Natl. Acad. Sci. U. S. A. 112, 15603–15608
  25. ↑ 25.0 25.1 Glibert, P.M. and Burford, M.A. 2017. Globally changing nutrient loads and harmful algal blooms: Recent advances, new paradigms, and continuing challenges. Oceanography 30: 58–69
  26. ↑ Bouwman, A.F., Beusen, A.H.W., Glibert, P.M., Overbeck, C., Pawlowski, M., Silveiva, J.H., Mulsow, S., Yu, R. and Zhou, M.J. 2013. Mariculture: significant and expanding cause of coastal nutrient enrichment. Environ. Res. Lett. 8, 044026
  27. ↑ Howarth, R.W., Swaney, D.P., Boyer, E.W., Marino, R., Jaworski, N. and Goodale, C. 2006. The influence of climate on average nitrogen export from large watersheds in the Northeastern United States. Biogeochemistry 79: 163–186
  28. ↑ Goes, J.I., Thoppil, P.G., Gomes, H.D.R. and Fasullo, J.T. 2005. Warming of the Eurasian landmass is making the Arabian Sea more productive. Science 308: 545–547
  29. ↑ Velthof G.L., Lesschen, J.P., Webb, J., Pietrzak, S., Miatkowski, Z., Pinto, M., Kros, J. and Oenema, O. 2014.The impact of the Nitrates Directive on nitrogen emissions from agriculture in the EU-27during 2000–2008. Science of theTotal Environment 468–469: 1225–1233
  30. ↑ Wells, M.L., Karlson, B., Wulff, A., Kudela, R., Trick, C., Asnaghi, V., Berdalet, E., Cochlan, W.,. Davidson, K., De Rijcke, M., Dutkiewicz, S., Hallegraeff, G., Flynn, K.J., Legrand, C., Paerl, H., Slke, J., Suikkanen, S., Thompson, P. and Trainer, V.L. 2020. Future HAB science: Directions and challenges in a changing climate. Harmful Algae 91, 101632
  31. ↑ Yu, Z.M., Song, X.X., Cao, X.H. and Liu, Y., 2017. Mitigation of harmful algal blooms using modified clays: theory, mechanisms, and applications. Harmful Algae 69: 48–64
  32. ↑ Inaba, N., Trainer, V.L., Onishi, Y., Ishii, K., Wyllie-Echeverria, S., Imai, I.and 2017. Algicidal and growth-inhibiting bacteria associated with seagrass and macroalgae beds in Puget Sounds, WA, USA. Harmful Algae 62: 136–147
  33. ↑ Inaba, N., Trainer, V.L., Nagain, S., Kojima, S., Sakami, T., Takagi, S. and Imai, I. 2019. Dynamics of seagrass bed microbial communities used to control artificial Chattonella blooms: a microcosm study. Harmful Algae 84: 139–150


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