Harmful Algal Bloom

Algae bloom in Lake Winnipeg in the Canadian province of Manitoba, with Reindeer Island visible in the lower-right part of the image. Image: contains modified Copernicus Sentinel data (2017), processed by ESA, CC BY-SA 3.0 IGO.


Harmful algal blooms (HABs) are proliferations of certain noxious and/or toxic micro- and macroalgae and cyanobacteria, regardless of their concentration, with negative impacts on aquatic ecosystems, and human health and wellbeing. HABs are naturally occurring phenomena that are also facilitated by anthropogenic pressures (including eutrophication, habitat modification and introduction of exogenous HAB organisms). HABs constitute a complex global problem that might increase in severity and frequency, and be expanded in biogeographic range, in our changing planet (GlobalHAB).

Facts and figures

Harmful algal blooms occur when colonies of algae grow out of control and produce toxic or harmful effects on people, fish, shellfish, marine mammals and birds. HABs occur naturally, but human activities that disturb ecosystems seem to play a role in their more frequent occurrence and intensity. Increased nutrient loadings and pollution, food web alterations, introduced species, water flow modifications and climate change all play a role. Studies show that many algal species flourish when wind and water currents are favorable. In other cases, HABs may be linked to “overfeeding.” This occurs when nutrients (mainly phosphorus and nitrogen) from sources such as lawns and agriculture flow into bays, rivers, and the sea, and build up at a rate that “overfeeds” the algae that exist normally in the environment. Some HABs appear in the aftermath of natural phenomena like sluggish water circulation, unusually high water temperatures, and extreme weather events like hurricanes, floods, and drought (NOAA).

HABs are natural processes that occur in all aquatic systems and cause worldwide problems with significant economic, socio-cultural, and human health consequences. There is considerable concern that some HABs and/or their associated impacts may be increasing and expanding globally due to a combination of natural and human-driven forcing, including climate change. In the past two decades, improvements in scientific understanding of the complex processes involved in HAB dynamics have contributed to better management of the risks associated with some harmful events (GlobalHAB).

Related content on the Knowledge Portal

Data Source

Screenshot of Global Ocean Chlorophyll
Publishing institution: Copernicus
The Copernicus Marine Environment Monitoring Service provides various products and services for marine applications. These include a global ocean physical analysis and forecast, biogeochemistry analysis and weekly forecast, global ocean waves analysis and forecast and in-situ observations. To the parameters observed belong: temperature, salinity, chlorophyll concentrations and many more.
Publishing institution: National Aeronautics and Space Administration (NASA)
NASA’s Ocean Biology Processing Group (OBPG) provides True Color, Chlorophyll and Sea Surface Temperature for download.
Publishing institution: National Oceanic and Atmospheric Administration (NOAA)
NOAA's Ecoforecasting Map locates site at risk of HABs, names prevalent species at the site and links directly to Alerts and Bulletins (forecasts) for the respective regions. The HABS Data Portal, is the portal for the great lakes (Lake Erie) mapping in-situ data useful in mapping algal blooms in the region. The phytoplancton monitoring network is a webmap which includes current weather radar, sampling locations and oceanographic data (SST,Salinity)
Publishing institution: Intergovernmental Oceanographic Commission (UNESCO/IOC), EOMAP
The World Water Quality Information and Capacity Building Portal (IIWQ) is a webmap that illustrates data on turbidity, chlorophyll-a, total absorption as well as the EOMAP specific harmful algal bloom indicator (HAB indicator). Where access to in-situ data is available station values are presented.
Publishing institution: Intergovernmental Oceanographic Commission (UNESCO/IOC), EOMAP
The World Water Quality Information and Capacity Building Portal (IIWQ) is a webmap that illustrates data on turbidity, chlorophyll-a, total absorption as well as the EOMAP specific harmful algal bloom indicator (HAB indicator). Where access to in-situ data is available station values are presented.
Publishing institution: Regional Organization for the Protection of the Marine Environment (ROPME)
The ROPME has initiated a regional program and special remote sensing unit for routine monitoring of marine and coastal environments in its regional marine area (the Gulf, Sea of Oman and Arabian Sea), which is conventionally, known as ROPME Sea Area. This program relies essentially on processing and utilization of real-time and near-real time satellite data from NASA’s MODIS sensor that is being received through the MODIS Direct Broadcast Receiving Station. This station has been installed at ROPME Secretariat in Al-Jabriya, Kuwait in early 2003 and still operative since that data. The station is being operated and managed by the experts of the Remote Sensing Unit (RSU) and routinely receives satellite data only from MODIS sensor onboard Terra and Aqua satellites. The RSU also provides a guidance and advice to the national focal points and other concerned authorities in case they need further information on status of the marine environment in their territorial waters or...
Publishing institution: Instituto di fomento pesquero (IFOP)
Set of maps developed by the Harmful Algal Studies Center (CREAN) of the Fisheries Development Institute (IFOP), whose purpose is to show the relative abundance of the Alexandrium catenella microalga, with the aim of informing and alerting about the presence of this dinoflagellate harmful. This information is preventive and in no case determines the opening and closing of seafood extraction areas.
Publishing institution: Copernicus
The map indicates chlorophyll-A and sea surface temperatures in the North Atlantic based on data. The products can be downloaded from the CMEMS catalogue using different protocol (ftp, wms...): NEAR REAL TIME (DAILY UPDATED) BASED ON SINGLE SENSOR (OLCI-A) AND MERGED SENSORS (MODIS-A & VIIRS-N): Global level-3 Daily: OCEANCOLOUR_GLO_CHL_L3_NRT_OBSERVATIONS_009_032 Global level-4 Climatology, Monthly, 8-days products and daily-Optimal-Interpolation: OCEANCOLOUR_GLO_CHL_L4_NRT_OBSERVATIONS_009_033 Atlantic level-4 Daily-Optimal-Interpolation: OCEANCOLOUR_ATL_CHL_L4_NRT_OBSERVATIONS_009_037 REPROCESSED TIME-SERIES BASED ON MERGED SENSORS (SeaWifs, MERIS, MODIS-A & VIIRS-N): Global level-3 Daily products: OCEANCOLOUR_GLO_CHL_L3_REP_OBSERVATIONS_009_085 Global level-4 Monthly, 8-days and Daily-Optimal-Interpolation: OCEANCOLOUR_GLO_CHL_L4_REP_OBSERVATIONS_009_082 Atlantic level-4 Daily-Optimal-Interpolation: OCEANCOLOUR_ATL_CHL_L4_REP_OBSERVATIONS_009_098 ACRI-ST ALSO...
Publishing institution: Instituto del mar del Peru (IMARPE)
La productividad del mar peruano es muy sensible a los efectos de El Niño-Oscilación del Sur. Se conoce que en años neutros y fríos (La Niña), la concentración superficial de clorofila-a (indicador de la biomasa del fitoplancton) en las aguas sobre el margen continental, varía entre 1.2 y 6.7 mg/m3, mientras que en años cálidos (El Niño) este rango tiende a reducirse a 1.2 - 2.6 mg/m3. Por ello, en IMARPE, complementariamente, se monitorea la clorofila-a superficial con la información que provee el sensor MODIS (Moderate Resolution Imaging Spectroradiometer, en inglés) con una resolución temporal diaria y espacial de 4 km.
Publishing institution: Intergovernmental Oceanographic Commission (UNESCO/IOC)
The Harmful Algal Information System, HAIS, will when fully established consist of access to information on harmful algal events, harmful algae monitoring and management systems worldwide, current use of taxonomic names of harmful algae, and information on biogeography of harmful algal species. Supplementary components are an expert directory and a bibliography. The HAIS System is being built within the "International Oceanographic Data and Information Exchange" (IODE) of the "Intergovernmental Oceanographic Commission" (IOC) of UNESCO, and in cooperation with WoRMS, ICES, PICES, IAEA and ISSHA. HAEDAT Disclaimer: The HAEDAT database contains information based on yearly national reports by ICES and PICES member states. The available information on individual events varies greatly from event to event or country to country. Monitoring intensity, number of monitoring stations, number of samplings, stations, etc. also varies greatly and therefore there is...


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