European regional assessment: Vulnerable (VU)
EU 27 regional assessment: Vulnerable (VU)

Coenagrion mercuriale is a near-endemic species for Europe and the majority of the populations are found in France. Here the species has an inferred decline of 25%. The decline is even worse in Spain and Portugal where the species decreased by nearly 80 %. On the other hand, the much smaller number of populations present in the UK, Belgium and Germany seems to remain stable or even increase in the case of Germany (Bowler et al. 2021). But the total number of populations remains very low and therefore the species is still assessed as Endangered in Germany. As the overwhelming number of populations are found in southwestern Europe, it is inferred that a decline of at least 30% has occurred over the last 10 years.

The severe decline in Spain and Portugal, and to a lesser extent also in France, might be caused by the desiccation of small streams due to rainfall deficit, increased water extraction for agricultural use and change of land use adjacent to the streams (conversion of meadows to arable fields). It is expected that future summer drying of small brooks due to global warming and more frequent long summer drought periods will result in a further decrease of the species over large areas in the next decades. Despite the fact that this species is listed in Annexes II and IV of the EU Habitats Directive and that Natura 2000 sites are designated to ensure its favourable conservation status, there are no indications that above mentioned threats will decrease. Therefore C. mercuriale is assessed as Vulnerable (A2ac+3c) for Europe and the EU27 Member States.

Coenagrion mercuriale is a near-endemic species for western Europe. Although the species occurs from southern Iberia to northern Germany and from the UK to Austria, the majority of the localities are found in France and to a lesser extent also in Spain and Portugal (Boudot and Prentice 2015). The species is extinct in the Netherlands where it has been always very rare with only a handful of records.

In has been erroneously recorded from Albania, Bulgaria, Hungary, Macedonia, Romania, Slovakia, Slovenia, and the Republic of Moldova. In nearly all those cases, the observations pertain to its very closely related sister species Coenagrion ornatum which inhabits the same habitat.

Outside Europe, subpopulations also occur in the Maghreb.

In Europe, the species is rather common in France. It is more scattered in Spain and Portugal, rare in Germany, and very rare in the United Kingdom, Belgium, Liechtenstein, Switzerland, Luxembourg, and Austria. The majority of subpopulations are found in France. Here the species has an inferred decline of 25%. The decline is even worse in Spain and Portugal where the species has decreased by nearly 80%. On the other hand, the much smaller number of subpopulations present in the UK, Belgium and Germany seems to remain stable, or in the case of Germany even shows a slight increase (Bowler et al. 2021). But the total number of subpopulations still remains very low and therefore the species is still assessed as Endangered in Germany. As the overwhelming number of subpopulations are found in southwestern Europe, a decline of at least 30% has occurred over the last 10 years.

C. mercuriale is found at unshaded, small streams and irrigation ditches characterised by rich aquatic and riparian vegetation. The species also occurs in seepage streams in peat and marshlands. The water of the small streams is generally more or less calcareous, shallow and slow-flowing, and most patches of organic detritus are present. The vegetation near the banks often consists of low herbs and grasses and is frequently used for hay production or grazing. It is one of the few species that is mainly found in agricultural areas (Boudot and Prentice 2015).

The main threats include water extraction, swamp and soil drainage, water table lowering through irrigation, meadow destruction and conversion towards other agricultural management, and water pollution. All modern intensive agricultural practices lead to the extirpation of the species. Drought in relation to global warming, forest closure and plantation of trees on river banks, poor management of bankside vegetation and the large scale of clearance of the ditches are also major threats.

Flourishing subpopulations still occur in many countries, but their survival is definitely incompatible with modern intensive agricultural practices and forest closure. Although the species remains widespread in France, most of the populations at the periphery of its main area have been lost and a continuous decline is observed in areas where agriculture shifts from grasslands to irrigated ploughed fields, the worst situation being reached with maize (a crop that is irrigated throughout the summer months) and rice cultivation.

The species is not utilised.

This species is included in the Annexes II and IV of the European Habitats Directive and in Appendix II of the Bern Convention (EEA 2023). The EU Directive states that member states of the EU27 must take the necessary measures so that the conservation status of the species is favourable. As a consequence, several action programs and actions were taken, often funded through EU LIFE projects. Main conservation measures include halting water pollution through wastewater treatment, and the management of watercourses that keeps the vegetation open. Intensification of agriculture should be avoided.