Impacts of Habitat Management on Larvae of the Damselfly Coenagrion mercuriale (Coenagrionidae, Odonata)—A Laboratory Study

Habitat management of small lotic waterbodies is essential to maintain flow and the quality of the habitats. For this purpose, aquatic plants are typically removed by authorities. This is done in a more or less disruptive manner, depending on the risk of interference with the bed. Since small lotic waterbodies are biodiversity-rich habitats, the effects of habitat management on macroinvertebrates need to be analyzed. In particular, we analyzed aquatic plant preferences, tolerance to sediment burial, and thanatosis to derive recommendations for current habitat management. A habitat choice experiment with larvae of the threatened damselfly Coenagrion mercuriale was conducted to identify preferences between four different aquatic plants, namely Callitriche spp., Elodea canadensis, Phragmites australis, and Veronica beccabunga, which are all typical C. mercuriale larval habitats. We aimed to investigate if specific aquatic plants should be avoided when removing aquatic vegetation during habitat management. In addition, we analyzed two further habitat management scenarios on larvae of C. mercuriale: fine sediment burial and thanatosis (reflex immobilization), which can both be induced by management machines. ... mehrThe habitat choice experiment showed no significant preferences for specific aquatic plants except for the direct comparison of V. beccabunga and Callitriche spp. We found that the majority of the larvae were tolerant to sediment burial of 1 cm; tolerance to thicker layers was rare. On absorbent paper, thanatosis duration differed between in-water and out-of-water. Larvae out-of-water stayed in thanatosis for longer, increasing the risk of predation when being removed with aquatic plants during management. The present study shows that different habitat management activities have impacts on C. mercuriale larvae. These impacts should be considered when choosing and performing appropriate management activities in small lotic waterbodies.