Limiting burrowing activity and overland dispersal of the invasive alien red swamp crayfish Procambarus clarkii by sophisticated design of watercourses

Abstract

Invasive alien crayfish species pose major ecological and hydrological risks globally. The red swamp crayfish (Procambarus clarkii) is one of the most widespread crayfish species worldwide. Its impacts arise from burrowing activities and lead to mobilization of soil nutrients, water safety risks by instability of dikes and erosion of banks. Increased sediment load demands additional dredging of drainage ditches and canals to ensure their water discharge capacity. Sustainable methods for limiting burrowing in banks and dispersal behaviour of crayfish were not yet available. Therefore, a field study was performed to determine whether the number of burrows and overland movement of crayfish were related to a particular bank type. Burrows were counted in three watercourses during a water-level decline. The number of burrows was significantly lower in natural banks than in non-natural and semi-natural banks. The construction of natural-like banks along watercourses may significantly reduce sediment load, erosion and the collapse of banks by burrowing activities of crayfish. An inclination experiment mimicking various types of terrestrial dispersal barriers elucidated that steepness, soil type and vegetation structure of small embankments near watercourses were significant factors for manipulating overland movement of crayfish. Crayfish were taken out of the water for this purpose and placed on small experimental embankments varying in slope and types of vegetation. The lowest frequencies of upward movement were recorded at inclinations of 20° and 30° on bare sandy soil and short and species-poor grassland substrates. This implies that crayfish crawling out of the water will return to the watercourse when encountering such a dispersal barrier. Therefore, a sophisticated design of embankments along watercourses can be a tool to reduce colonization risk of nearby located, hydrologically isolated water bodies with high nature values.