title: River bank burrowing by invasive crayfish: Spatial distribution, biophysical controls and biogeomorphic significance.
abstract: Invasive species generate significant global environmental and economic costs and represent a particularly potent threat to freshwater systems. The biogeomorphic impacts of invasive aquatic and riparian species on river processes and landforms remain largely unquantified, but have the potential to generate significant sediment management issues within invaded catchments. Several species of invasive (non-native) crayfish are known to burrow into river banks and visual evidence of river bank damage is generating public concern and media attention. Despite this, there is a paucity of understanding of burrow distribution, biophysical controls and the potential significance of this problem beyond a small number of local studies at heavily impacted sites. This paper presents the first multi-catchment analysis of this phenomenon, combining existing data on biophysical river properties and invasive crayfish observations with purpose-designed field surveys across 103 river reaches to derive key trends. Crayfish burrows were observed on the majority of reaches, but burrowing tended to be patchy in spatial distribution, concentrated in a small proportion (<10%) of the length of rivers surveyed. Burrow distribution was better explained by local bank biophysical properties than by reach-scale properties, and burrowed banks were more likely to be characterised by cohesive bank material, steeper bank profiles with large areas of bare bank face, often on outer bend locations. Burrow excavation alone has delivered a considerable amount of sediment to invaded river systems in the surveyed sites (3tkm(-1) impacted bank) and this represents a minimum contribution and certainly an underestimate of the absolute yield (submerged burrows were not recorded). Furthermore, burrowing was associated with bank profiles that were either actively eroding or exposed to fluvial action and/or mass failure processes, providing the first quantitative evidence that invasive crayfish may cause or accelerate river bank instability and erosion in invaded catchments beyond the scale of individual burrows.
authors.affiliation: School of Geography, Queen Mary University of London, UK.
authors.forename: Matej
authors.initials: M
authors.lastname: Faller
authors.affiliation: School of Geography, Queen Mary University of London, UK. Electronic address: g.l.harvey@qmul.ac.uk.
authors.forename: Gemma L
authors.initials: GL
authors.lastname: Harvey
authors.affiliation: School of Geography, Queen Mary University of London, UK.
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Henshaw
authors.affiliation: Department of Civil, Environmental and Mechanical Engineering, University of Trento, Trento, Italy.
authors.forename: Walter
authors.initials: W
authors.lastname: Bertoldi
authors.affiliation: Sustainable Agro-ecosystems and Bioresources Department, Fondazione E. Mach, IASMA Research and Innovation Centre, San Michele all' Adige, Trentino, Italy.
authors.forename: Maria Cristina
authors.initials: MC
authors.lastname: Bruno
authors.affiliation: Environment Agency, Wallingford, England, UK.
authors.forename: Judy
authors.initials: J
authors.lastname: England
mesh_terms: D000818:Animals; D003400:Astacoidea / Q000502:physiology*; D017753:Ecosystem; D004739:England; D019015:Geologic Sediments / Q000032:analysis*; D058865:Introduced Species; D045483:Rivers
keywords: Bank erosion; Biogeomorphology; Ecosystem engineer; Invasive species; Sediment dynamics; Signal crayfish