Excessive growth of plankton algae increases the amount of organic matter settling to the bottom. Harmful algal blooms may cause discoloration of the water, foam formation, oxygen depletion, death of benthic fauna and wild or caged fish, or shellfish poisoning of humans. Increased growth and dominance of fast growing filamentous macroalgae in shallow sheltered areas is yet another effect of nutrient overload which will change the coastal ecosystem, increase the risk of local oxygen depletion and reduce biodiversity and nurseries for fish.

More on algal blooms in particular and on eutrophication in general in the EEA report Eutrophication in Europe's coastal waters. The structure of the report generally follows the DPSIR assessment framework, where D = driving forces, P = pressures, S = state, I = impacts and R = responses. The DPSIR framework for marine eutrophication is illustrated in Figure 1. Driving forces and source apportionment are not main topics and are only briefly mentioned in this report, which concentrates on pressures, state, impacts and responses.

Other reports from EEA on algal blooms and eutrophication:

• Remote sensing's contribution to evaluating eutrophication in marine and coastal waters
• State and pressure of the marine and coastal Mediterranean environment
• Nutrients in European ecosystems
• Environmental signals 2002: Chapter 11 - Inland and coastal waters
• Europe's environment: the third assessment: Chapter 8 - Water

• Chlorophyll-a concentrations in European marine waters

Other sources for information on algal bloom

Several institutions in Europe are involved in the monitoring and assessment of eutrophication using satellite images and can supply more detailed information on specific areas.

Figure 2: Satellite image on algal bloom in Danish and German waters
Source: DMI, image enhanced by PhD. Peter Viskum Jørgensen, DMI.
Note: The image is made by the Aqua-satellites MODIS-instrument (Moderate-Resolution Imaging Spectroradiometer) on Thursday 7 August 2003 at 14:00. The algae are visible as the white and green colored strings in the water.

Links:

• Daily updated satellite images on Norway: http://www.nersc.no/Decide-HAB/
• Weekly info on health risks (norwegian): http://algeinfo.imr.no/
• Annual maps: http://www.ifremer.fr/envlit/documentation/dossiers/ciem/aciem-c1.htm
• Baltic Sea Portal - Less cyanobacteria in sea areas: http://www2.fimr.fi/en/itamerikanta/levatiedotus/uutisarkisto/278.html
• Baltic Sea Portal - Map with blue-green algal blooms: http://www2.fimr.fi/en/itamerikanta/levatiedotus/levakartat.html