Rhine-Westphalia

Status and conservation of Coenagrion mercuriale in North Rhine-Westphalia Christian Cocking, Thomas Hiibner & Kirsten Rohr Introduction France, with its main distribution area in south- The Southern Damselfly (Coenagrion mercuriale) western Europe (Dukstra & Lewington, 2006). occurs in meadow brooks, ditches and lime fens Several localities are known further north, in rich in vegetation. The species is threatened Belgium (De Knijf et al., 2006) and in southern all over Europe. It is indicated as a species of England. The northern limit of its distribution community interest in Appendix II of the Habitats runs through northern Germany; there are single Directive of the EU and listed as ‘near threatened’ populations in the federal states of Brandenburg in the IUCN Red List of threatened species. In and Niedersachsen. In the Netherlands, only recent years, a network of protected areas has two records are certain, the last one a larva been designated in order to ensure this species found near Winterswijk in 1929 (NVL, 2002). occurrence in North Rhine- Westphalia (NRW). In Germany, NRW is the stronghold for this C. The species present and status, the structure of mercuriate and there are chances for succesful its habitat in NRW are described, as well as the conservation. conservation measures needed. C. mercuriale (figure 1) is an Atlanto- Distribution in North Rhine-Westphalia Mediterranean species. It is quite common in To our present knowledge, there are about North Africa, the Iberian peninsula, Italy and twelve populations of C. mercuriate in North Figure 1. Male Coenagrion mercuriale (Photo:R. Ketelaar). Brachytron 12:11-17, 2010 11 Figure 2. The distribution of Coenagrionmercuriale in NRW and the Netherlands (1995-2003). Rhine-Westphalia. Most of them are located in while at the edge of villages, it runs through the Westphalian lowland, on the floodplain of the meadows. Some stretches are in forested rivers Ems and Lippe (figure 2). All populations, areas. except the one at Thielenbruch near Cologne, are situated below an altitude of 100 m above Talgräben of the river Ems sea level (Cocking et al., 2007). Two populations The presence of populations of C. mercuriale in are especially interesting because these are well the Ems valley has been known since the late studied. They are presented in more detail in the 1980s. Regular, but non-systematic, research following paragraphs. has been carried out in recent years. A more detailed research into its present status was Emmerbach carried out in 2005. South of Münster, near Davensberg, there is a Due to this investigation, the parts of the ditches population which was known by Vornefeld as with the highest concentrations of C. mercu- early as 1939 (Gries & Oonk 1975). Mapping riale are now known (figure 3). One of these projects between 2003 and 2006 brought to lies in the northern valley ditch and is about light that, with more than 500 individuals this is 10 km long. Another one of about 15 km long probably one of the largest populations in NRW. is present in the southern valley ditch. Both of C. mercuriale is present along the Emmerbach these populations are however interrupted by (figure 4), occupying about 15 km, spread out stretches of water that are unsuitable for C. over a stretch of 36 km in total. This slow-flowing mercuriale, either because they are shaded, brook has been changed much by human or because the flow velocity is too low for the activity. There are no meanders or eroded necessary plant communities to occur. banks along the water course. The stream bed The Ems alluvial plain, including the valley is sandy-loamy, the stream bank contains a lot ditches, was completely canalised in the 1930s. of pebbles. The brook runs mostly through an The ditches lie at the northern and southern intensively cultivated, agricultural landscape edge of the alluvial plain, running in western dominated by fields of maize and other grains, direction. Fed by seepage, they drain the alluvial 12 plain. The light, sandy soil, and the constant soil but at present there are clearly fewer individuals. moisture level make the Ems alluvial plain and Near Thielenbruch medium to large populations its surroundings ideal for growing maize and can be found in the ditches of Tiefenriede, in other grains. The water level in the valley ditches Minden-Lubbecke (known thanks to Clausen is regulated by dams and small weirs. There are since 1980) and Dattelner Muhlenbach. There meanders. no plunge pools or are two other small populations, one in the The areas with the largest populations of C. Loddenbach, in the district of Gutersloh, and mercuriale are characterised by a comparatively the other in an affluent of the Eltingmuhlenbach, flow high rate, a sandy substrate low in detritus, in Steinfurt. Besides these populations, some and submerged and emergent, herb-rich single records or temporary populations are vegetation. known in NRW. In the district of Steinfurt, a single dead individual was found in a spiderweb. Other locations In the district of Soest, one flying animal was There are more populations elsewhere in NRW. observed and a temporary small population was A detailed description of the knowledge ofthese present on the Liese in the district ofWarendorf. populations with notes of their conservation status is given in Gocking et al. (2007). One Although most populations are well studied, it of these populations is in the Tallewiesen is likely that more populations can be found. near Paderborn, where the species is known Recently, there are some indications that the since 1988. The oldest known at population, species might expanding its range, possibly Thielenbruch in Cologne, was described in 1979 due to climatic changes. Extensive research in as a ‘strong, indigenous population'. It still exists, suitable habitats might reveil more populations. Figure 3. Habitat ofCoenagrion mercuriale at Talgraben (Photo: N. Menke). Brachytron 12:11-17, 2010 13 Habitat in North Rhine-Westphalia C. mercuriale mostly inhabits smaller, sunny waters with well-developed submerged and emergent vegetation (see details in Göcking et al. 2007). In Thielenbruch, one population occurs in a lime fen. Other populations are present in dike-systems, like in Tiefenriede and in the Ems valley ditches, but also in canalised flowing waters, such as the Emmerbach, Ortsteinbach and Tallewiesen. The Dattelner Mühlenbach is the only semi-natural meadow brook in the area, and the occurrence of C, mercuriale shows that this species can occur in semi-natural flowing waters in NRW, as long as appropriate structures are present. It is essential that the water never freezes or dries up, but also important that the flow velocity is not too high. Due to the low flow velocity, in some parts of inhabited brooks, communities of macrophytes are present, with floating-leaved species, such 4. Figure The Emmerbach, one of the strongholds of as Nupharlutea and Potamogeton natans. Coenagrionmercuriale in North Rhine-Westphalia(Photo: However, most segments of the brook where C. N. Menke). mercuriale is present are characterised by: • running water with a higher flow velocity and Phalaris arundinacea in the lime fen at rich in oxygen, Thielenbruch is remarkable since these plants • stream bedding poor in detritus occur in all other locations. The species avoids • submerged and emergent vegetation stretches with dense, tall vegetation, such as with Berula erecta, Myosotis palustris, reeds (Phragmites australis). Large numbers of Mentha aquatica, Nasturtium offici- Nuphar lutea with their large floating leaves are nale unfavourablefor the species, because of the high • sunny conditions in the whole brook cover. The presence of submerged vegetation is • highly structured vegetation close to essential, being a habitat requirement for the the water larvae (Müller, 2003, Röhr, 2005). The cover of the submerged vegetation should always be The first three factors seem to be important for more than 10%. An optimum of approximately the larvae. Highly structured vegetation close to 40% can be found in the Ems valley ditches. the water is important for the adults as a hunting A well-developed submerged and emergent and site. Such mating vegetation may be found vegetation with Berula erecta seems to be in in fallow essential. riparian zones, fields, but also in Moreover, submerged Callitriche, , or mown wet meadows, reed beds or extensively in Thielenbruch, Characea , is often found in the grazed meadows. The most important habitat habitat of C. mercuriale. requirement for C. mercuriale is therefore the vegetation structure. In an analysis of the Threats ditches of the Ems valley (Müller, 2003), Muller C. mercuriale is classified in the Red Data observed that in locations with C. mercurials, Books of Germany (1998) and NRW (1998) the emergent vegetation had a cover of 20-60%. as an endangered species. It is mentioned in A vegetation cover of more than 90% is not Appendix II of the FFH-Guidelines. Therefore, tolerated. The Berula absence of erecta special conservation measures must be 14 Figure 5. Tandem Coenagrion mercuriale (Photo R. Ketelaar). implemented for this species, and conservation Conservation areas have to be designated. In NRW, the The most important conservation measure problems for conservation management have is oriented towards the maintenance of already been published (Gocking et al 2007 vegetation. and (www.LANUV.NRW.de) The most important Appropriate management and maintenance threats are: measures help maintain the vegetation structure • Inappropriate maintenance. Maintenance that C. mercuriale (figure 5) requires in its can be too intensive, leaving vegetation habitat: structure. • with no Lack of maintenance is Weeding should only be done if necessary, also too at in a threat, leaving much vegetation most, once 2-3 years; it should only be on the bank, which is unfavourable to C. done in parts. mercurials, especially in combination with • Clearing the stream bed in parts with more shade due to trees.

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