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

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...
Publishing institution: National Oceans and Coastal Information Management System (OCIMS) South Africa
Webmap of Algal bloom detections, CHl-A from MODIS nFLH, Sea Surface Temperature (Odyssea), Chlorophyll-A from Sentinel OLCI. The HAB Decision Support Tool (DeST) provides a capability for monitoring and assessing risk of HAB events for the South African coastal area to approximately 50km offshore. Risk assessment and monitoring is based on quantified understanding of bloom dynamics (Pitcher & Nelson, 2006), hypoxic impacts (Pitcher et al 2014), and earth observation monitoring capabilities (Bernard et al 2006). Maps of various ocean colour-derived phytoplankton biomass proxies, sea surface temperature, and ocean state (wind, current, sea state) are used to provide information on the presence and movement of blooms, and extracted time series of these data provide a "virtual buoy" capability giving a multi-parameter risk index.
Publishing institution: National Oceanic and Atmospheric Administration (NOAA)
HABSOS combines in-situ measurements, with oceanographic and meteorological data. When clicking on metadata in the website the 15+ integrated data sources can be viewed.

GP-STAR factsheet

Publishing institution: United Nations Office for Outer Space Affairs (UNOOSA)
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Publishing institution: United Nations Office for Outer Space Affairs (UNOOSA)

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Publishing institution: UNITAR Operational Satellite Applications Programme (UNOSAT)

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