Myocastor coypus (coypu) burrows undermine the banks of rivers and dykes causing instability (Carter and Leonard, 2002). Feeding on rhizomes and young shoots of marsh plants leads to plant community breakdown and can lead to erosion in coastal habitats (LeBlanc, 1994). Coypu feeding on sea oat rhizomes in Mississippi barrier islands have led to sand dune erosion in these important habitats (GSMFC 2005).
At high densities coypu are able to convert marshland to open water by feeding on plants. Habitat destruction caused by coypu threatens rare marshland species of bird, fish and invertebrates. In Italy coypu have caused breeding whiskered tern (Chlidonias hybrida) to decline by largely destroying the cover of water-lilies Nymphaea in Valli di Argenta a designated IBA (Important Bird Area). The habitats of two national treasure species in Japan - a critically endangered dragon fly (see Libellula angelina in IUCN Red List of Threatened Species) and a fish the vulnerable deep-bodied bitterling (see Acheilognathus longipinnis in IUCN Red List of Threatened Species) (Shirow Tatsuzawa, pers. Comm.) are threatened by coypu.
Coypu also feed on agricultural crops (Carter and Leonard 2002) including sugarcane, alfalfa and root crops (Woods et al. 1992)
Location Specific Impacts:
Agricultural: Coypu are presently regarded as a pest species in Italy due to the damage they cause to rice farms. In a 2003 written communication, Piero Genovesi calculated that between 1996 and 2000, coypu caused 14 million euros in damage, and further losses from each year are projected to rise 9-12 million euros
Agricultural: Coypu cause minor damage to river and pond systems (Tatsuzawa, S., pers. comm., 2004).
Predation: Coypu eat native freshwater mussels. Some native fish species which lay their eggs in these mussels have become locally extinct. Two fish species predicted to be threatened in this manner are the Nippon-Bara-tanago or Japanese rose bitterling (Rhodeus ocellaus kurumeus) and the vulnerable Itasenpara or deepbody bitterling (see Acheilognathus longipinnis in IUCN Red List of Threatened Species), are listed in the Japanese Red Data Book of endangered species. A. longipinnis is endemic to small parts of Honshu and is a Japanese national natural treasure (Tatsuzawa, S., pers. Comm., 2004).
Reduction in native biodiversity: Coypu eat water plants that sustain native insect fauna. This has caused the local extinction of many insects that depend on the natural flora, including some species of dragon fly. One dragon fly species threatened with extinction is the critically endangered or Bekkou-tombo (see Libellula angelina in IUCN Red List of Threatened Species). Bekkou-tombo is related to species of painted grasshawk. It is endemic to Japan and is a Japanese national natural treasure (Tatsuzawa, S., pers. Comm., 2004).
Agricultural: Coypu damages the sugar beet crop in the Netherlands and is therefore being considered a candidate for eradication by European agencies. (Litjens, 1980; in Carter, 2007)
United Kingdom (UK)
Human nuisance: Coypu disrupted drainage systems in East Anglia due to their extensive borrow systems in river banks, and thus caused a flood risk. It also damaged agricultural crops (Gosling and Baker, 1989)
Reduction in native biodiversity: Myocaster coypus destroyed large areas of reedswamp (Gosling and Baker, 1989)
Threat to endangered species: Coypu added to the decline of cowbane Circuta virosa, whicih is now a Nationally Scarce species in Britain. (Gosling and Baker, 1989)