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You are here: Home / Data and maps / Indicators / Chlorophyll in transitional, coastal and marine waters / Chlorophyll in transitional, coastal and marine waters (CSI 023) - Assessment published Mar 2013

Chlorophyll in transitional, coastal and marine waters (CSI 023) - Assessment published Mar 2013

Indicator Assessmentexpired Created 21 May 2012 Published 26 Mar 2013 Last modified 03 Mar 2015, 11:58 AM
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This content has been archived on 03 Mar 2015, reason: Other (New version data-and-maps/indicators/chlorophyll-in-transitional-coastal-and-2/assessment was published)

Generic metadata


Water Water (Primary topic)

Coasts and seas Coasts and seas

soer2010 | thematic assessments | water | coastal water | chlorophyll-a | marine and coastal | ecosystems | coastal ecosystems
DPSIR: State
Typology: Descriptive indicator (Type A - What is happening to the environment and to humans?)
Indicator codes
  • CSI 023
Temporal coverage:
Geographic coverage:
Albania, Belgium, Bosnia and Herzegovina, Bulgaria, Croatia, Cyprus, Denmark, Estonia, Finland, France, Germany, Greece, Ireland, Italy, Latvia, Lithuania, Malta, Montenegro, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovenia, Spain, Sweden, Turkey, United Kingdom

Key policy question: Is eutrophication in European surface waters decreasing?

Key messages

  • In 2010, the highest summer chlorophyll-a concentrations were observed in coastal areas and estuaries where nutrient concentrations are also generally high (see CSI 021 Nutrients in transitional, coastal and marine waters). These include the Gulf of Riga, Gulf of Gdansk, Gulf of Finland and along the German coast in the Baltic Sea, coastal areas in Belgium and The Netherlands in the Greater North Sea and in few locations along the coast of Ireland and France in the Celtic Seas and Bay of Biscay, respectively. High chlorophyll concentrations were also observed along the Gulf of Lions and in Montenegro coastal waters in the Mediterranean Sea, and along Romanian coastal waters in the Black Sea. Low summer chlorophyll concentrations were mainly observed in the Kattegat and open sea stations in the Greater North Sea, and in open sea stations in southern Baltic Sea. 
  • Between 1985 to 2010, decreasing chlorophyll concentrations (showed in 8% of all the stations in the European seas reported to the EEA) were predominantly found along the southern coast of the Greater North Sea, along the Finnish coast in the Bothnian Bay in the Baltic Sea and in a few stations in the Western Mediterranean Sea and Adriatic Sea. In the Black Sea, it was not possible to make an overall assessment due to the lack of time series data. Increasing concentrations (observed in 5% of the reported stations) were generally observed in coastal locations in the Northern Baltic Sea but also in the open sea stations outside the north of the Celtic Seas. Most stations (87%) however showed no changes over time.

Chlorophyll-a concentrations in European seas in 2010

Note: The map shows Chlorophyll-a concentrations in European coastal and open seas in 2010. The class boundaries “high”, “moderate” and “low” concentration are determined by the 80/20 percentiles of the data set in each sea (sub)region. The low category refers to values within the lowest 20th percentile and the high category refers to values within the upper 20th percentile of concentrations.

Data source:
Downloads and more info

Observed change in chlorophyll-a concentrations in coastal and open waters of the Baltic, North East Atlantic and Mediterranean Sea, 1985-2010

Note: The map shows stations with a statistically significant decrease (green), increase (red) or no trend (yellow) within the period 1985-2010. Selected stations must have at least data in the period from 2007 to present and at least 5 years data in all. Note that the open sea stations around Faroe Islands are included under Celtic Seas.

Data source:
Downloads and more info

Key assessment

Baltic Sea

In 2010, the highest measured summer chlorophyll-a concentrations (>12.2 µg/l) were found in German  waters along the Mecklenburg coast and the Gulf of Gdansk, and in a few locations in the Gulf of Riga and Finalnd. Low concentrations were predominantly observed in the open waters of the southern Baltic Sea (Figure 1).

Most of the stations (87%) did not show a significant change in chlorophyll concentration in the period 1985-2010. Overall, statistically significant decreasing trends were evident in 7% of the Baltic Sea stations (Figure 2). Chlorophyll concentrations decreased in Finnish coastal areas of the Bothnian Bay and at discrete stations in the Baltic Proper. In contrast, increases were observed in particular in the Gulf of Finland, and at some coastal stations in the Gulf of Bothnia and along the southern Baltic coast. Statistically significant increasing trends were evident in 7% of the Baltic Sea stations (Figure 3). In fact, HELCOM (2009, 2010) recognizes that eutrophication is a problem in large parts of the Baltic marine ecosystem.

Greater North Sea

In 2010, the highest summer chlorophyll-a concentrations (> 8.9 µg/l) were observed along the coast of Belgium and The Netherlands (Figure 1). These areas are also characterized by elevated concentrations of nutrients (see CSI 021) and frequent blooms of Phaeocystis globosa (OSPAR, 2008). According to OSPAR (2010), further actions are needed to improve problem areas like the continental coast of the Greater North Sea. Low chlorophyll concentrations were predominantly observed in the open waters of The Netherlands and in the Kattegat (Figure 1).

The majority of the stations (88%) did not show a statistically significant change in chlorophyll concentration between 1985 and 2010. In 10% of the stations, found in transitional and coastal waters along the continental coast, a statistically significant decreasing trend was observed whereas 2% of the stations (located in the open sea) showed an increasing trend (Figure 2, 3). 

Celtic Sea, Bay of Biscay and the Iberian coast

Generally, chlorophyll concentrations in the Celtic Seas, Bay of Biscay and the Iberian coast were generally low (< 2 µg/l) in 2010, with the exception of a few transitional water stations along the Irish and French coast (Figure 1). OSPAR (2008) has defined small coastal embayments and estuaries within the Celtic Seas and the Bay of Biscay and Iberian Coast as problem areas with respect to eutrophication.

A significantly increasing trend was observed in 15% of the stations, predominantly in open sea stations, whereas no trend was observed in the majority of the other stations (Figure 2, 3). 

Mediterranean Sea

In 2010, only data from France,Croatia and Montenegro were available (Figure 1). The highest summer chlorophyll-a concentrations (> 5 µg/l) were observed in transitional and coastal waters of France and Montenegro. No offshore data of the Mediterranean chlorophyll concentrations have been reported to the EEA for the year 2010. The open waters of the Mediterranean Sea are, however, poor in nutrients and thus summer chlorophyll-a concentrations are also low. 

Only France and Croatia have submitted long enough time series data to estimate trends. In 12% of these Mediterranean stations, significant decreases were observed, while no increases were observed in any of the stations. Significantly decreasing trends were observed in 16% of the French stations, mainly in the Gulf of Lions and in one (5 %) of the Croatian stations (Figure 2, 3). 

Recent regional assessments show that nutrient over-enrichment, possibly leading to eutrophication and hypoxia, occur mainly in developed coastal areas and are among the pressures and impacts that are common to all four subregions in the Mediterranean (Western Mediterranean, Central Mediterranean and Ionian, Adriatic Sea, Eastern Mediterranean) (UNEP/MAP, 2012).The most eutrophic waters in Mediterranean are along the northern coastline, but eutrophication problem has been increasing gradually over the last decades also in the southern shore of the sea (UNEP/MAP 2007). Harmful algal blooms have been observed commonly in the northern coastal areas. These blooms have also consisted of dinoflagellates (e.g. Dinophysis and Alexandrium) potentially causing different types of shellfish poisoning (Koukaras and Nikolaidis 2004, Bravo et al. 2008).

Black Sea

Black Sea data for the year 2010 consisted of a number of coastal measurements along the Romanian coast near the Danube estuary, which showed high to moderate levels of concentration. The time series was too short to perform a trend analysis.


Data sources

More information about this indicator

See this indicator specification for more details.

Contacts and ownership

EEA Contact Info

Constança De Carvalho Belchior


EEA Management Plan

2012 1.5.2 (note: EEA internal system)


Frequency of updates

Updates are scheduled once per year in July-September (Q3)
European Environment Agency (EEA)
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1050 Copenhagen K
Phone: +45 3336 7100