European regional assessment: Least Concern (LC)
EU 27 regional assessment: Near Threatened (NT)

Euglesa conventus is an Alpine species in western Europe, restricted to Alpine lakes, but found in northern temperate and Arctic areas in the north and present in suitable habitats in the northern part of the range. Specific threats include organic pollution in France and Switzerland, where some subpopulations have been lost. The species may also be impacted by agricultural pollution in Scandinavia. As this species inhabits cold waters in lakes and tarns, their water temperature may be adversely compromised by future climate change. Overall, the species is assessed as Least Concern (LC) at the European level as it is assumed that the species has a wider distribution than known at present in European Russia, and subpopulations are likely to be stable.

In the EU27 Member States, some subpopulations have been lost as a result of pollution in the southern part of its range, and pollution may also impact known Scandinavian subpopulations. There is an absence of data on the population trend in the EU, however, a continuing decline in the number of subpopulations is inferred from the current threats. An assessment of Near Threatened for the EU 27 is applied here on a precautionary basis, as it is suspected that the rate of population decline may approach the threshold (i.e. 30%) for VU under Criterion A3 (A3c) in the next ten years. Although the species can be transported by birds, any rescue effect is considered insignificant. Monitoring is required for this species in the EU.

This species has a holarctic distribution but is restricted to cold water, either in circumpolar areas or at high elevations.

In Europe, it mainly has a relictual distribution in high altitude lakes, hence it has a scattered range, and is localised everywhere. It is listed (Welter-Schultes 2012) as occurring in the Faroe Islands (Denmark), Norway, Sweden, Finland, Lithuania, Poland, Republic of Ireland (Eire), Great Britain (UK), France (mainland), Germany, Switzerland, Austria and mainland Italy mainland. This is a rare species in Britain, having been recorded only from Snowdonia in Wales, Helvelyn in the English Lake District, and a few locations in Scotland. In Italy, there are three localities. In France, the species is present in alpine lakes and in one location in the Vosges. Five localities are situated outside the Alpine area in Germany.

Out of the European region, the species range extends to Siberia east to the Russian Far East, and to the Great Lakes in North America, and has also been recorded for Japan. It is found at high at lower elevations across North America and Eurasia.

There are no population data available for this species. Its population is fragmented (although birds probably play a role in genetic mixing). Some known lake populations have been lost in France (Mouthon 2017) and in Switzerland. In the EU27, the population is declining, but populations are likely to be more stable across its northern distribution.

Euglesa conventus is typically a lacustrine and northern species. In the south of its range, it is a relict species from the Ice Age that occurs in high-altitude alpine lakes only. In the northern part of its range, it is found in the littoral zone of lakes in northern Norway and in the colder parts of deep lakes in southern Norway (Kuiper et al. 1989) and inland areas in Sweden, probably at lower elevations. In Sweden, there are also records from streams and rivers close to lakes.

It is found in the profundal zone (below the range of effective light penetration, down to 300 m) of large lakes. It occurs mostly in cold mountain tarns and lakes and also in deep lochs at lower altitudes (e.g. Loch Ness). It is adapted to a narrow range of environmental conditions and its optimum temperature conditions are 3.86°C-6.85°C (Killeen et al. 2004). It tolerates a lack of calcium.

Apart from global warming, there may be anthropogenic pressure on the environments it occupies in the form of water pollution in touristic places (Mouthon 2017).

The species is sensitive to both sewage and domestic pollution and this has impacted some populations in Switzerland and France. Agricultural pollution (nutrient inputs) may impact the species in Norway where it occurs in agricultural areas. The species' habitat in lakes and tarns is threatened by conversion of the water bodies into reservoirs, but in general it is unlikely that the lakes in which this species lives are under threat from drainage. However, their water temperature may be adversely compromised by future climate change.

This species is not utilised or traded.

No conservation actions targeting this species are currently in place. Several sites in Norway are in protected areas. In some countries in the southern part of the range it is considered to be a species of conservation interest, as these habitats could be compromised by climate change. In Great Britain this species is listed as Vulnerable, based on few locations (unpublished manuscript, M. Seddon and I. Killeen pers. comm. 2009). In France, this species is listed as Vulnerable based on the few locations, the ongoing decline and the current threats (pollution and climate change), and it is also listed as Vulnerable in Poland.

Future conservation measures should focus on protecting the habitats that the species occurs in. Further research should be carried out into the population size and trends, as well as the specific threats facing this species.