Chlorophyll in transitional, coastal and marine waters in Europe (Indicator)

Key messages: Monitoring chlorophyll-a levels is key for assessing coastal and marine water quality. 95% of monitoring stations in Europe’s seas revealed no significant trend. Between 1980 and 2021, the number of locations with decreasing trends exceeded the number of locations with increasing trends in all sea regions. These findings highlight the ongoing risks of eutrophication for Europe’s seas.

Measurements of the mean concentrations of chlorophyll-a in the sea reflect natural differences between low, medium and high levels of biological productivity.

Although chlorophyll-a is not harmful, elevated levels can indicate excessive nutrient enrichment, either from anthropogenic or natural sources. Such excesses can lead to eutrophication, reducing biodiversity, degrading ecosystems, enabling harmful algae blooms and causing oxygen deficiency in bottom waters.

Given this, monitoring chlorophyll-a is key to tracking coastal and marine water quality. A total of 150 locations out of 264 monitored in Europe’s seas between 1980-2021 showed that conditions were improving in the Kattegat Strait and around north-western Ireland. The remaining 114 locations showed chlorophyll-a levels were increasing (see Figure).

Trends in chlorophyll-a levels vary across locations in Europe’s seas. No significant trends were observed in 82.5-97.1% of the locations depending on the marine region. Increases in chlorophyll-a levels are still observed in several locations in all regions except the Black Sea, where a limited number of observations were available.

Please consult the relevant indicators and signals below for a more comprehensive overview on the topic.

Zero Pollution Action Plan 2030 target or policy objectives

Reduce nutrient losses by 50% .
Minimise human-caused eutrophication to achieve good environmental status (EU, 2008).

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Ecosystems

Zero pollution monitoring assessment

Nutrients in Europe's transitional, coastal and marine waters (Indicator)

Marine waters affected by eutrophication (Indicator)

Hazardous substances in marine organisms in European seas (Indicator)

References and footnotes

EU, 2008, Directive 2008/56/EC of the European Parliament and of the Council of 17 June 2008 establishing a framework for community action in the field of marine environmental policy (Marine Strategy Framework Directive) (OJ L 164, 25.6.2008, p. 19-40)
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