Short description of Crangonyx pseudogracilis, Northern River Crangonyctid

This amphipod shrimp is of bluish-white colour, has well developed black eyes and a length of 4-7 mm. It can be recognised by its distinctive locomotory behaviour as unlike other amphipods, it does not crawl on its side but walks upright like a talitroid.

Impact summary: Crangonyx pseudogracilis, Northern River Crangonyctid

It may replace native species and cause widespread community disturbance, though there is also evidence that it can co-exist with native amphipod species.

Habitat summary: Crangonyx pseudogracilis, Northern River Crangonyctid

This shrimp inhabits a wide variety of aquatic habitats including lakes, permanent and temporary ponds, rivers, streams and even interstitial habitats. It often occupies the most polluted areas of a river where no native freshwater shrimp can be found.

Overview table

Environment	Freshwater
Species status	Non-Native
Native range	Northern America
Functional type	Herbivore
Status in England	Non-Native
Status in Scotland	Non-Native
Status in Wales	Non-Native
Location of first record	London (17, 21)
Date of first record	1935

Origin

North American (USA and Canada).

First Record

1935 in London (Hackney), and 1936 in filter beds at Lea Bridge Waterworks.

Pathway and Method

The means of introduction into GB are unclear but it may have been accidentally introduced on garden(-pond) plants. Introduction into Scotland was probably independent via timber imported from Canada.

Species Status

After its introduction into England in the mid 1930s, it has continuously spread across England and Wales, and is probably still expanding its range. It was probably independently introduced into Scotland, where it was first discovered in 1958 in a timber seasoning pond at Grangemouth. In 1960, it was found in Windermere, and occupied a variety of littoral habitats throughout the entire lake within just 4 years. First discovered on Isle of Man in 1995, where it has spread since. In the mid 1980s, it was first discovered in Northern Ireland and has spread there since. Other European countries invaded by this species include the Netherlands, Belgium, France, Germany and Ireland.

Dispersal Mechanisms

Live specimens have been observed in holding tanks for ornamental aquatic plants, so transfer of such plants may provide an ideal mode of dispersal for the species. Its ability to colonise temporary ponds is probably facilitated by its ability to survive and disperse in shallow groundwater.

Reproduction

Life span of about 2 years, with one female producing up to 8 broods. Sexual maturity is reached at about 60-100 days. Unlike native species, females engage in brood care such as flushing the brood with water and cycling the eggs within the brood pouch. Amelioration of environmental conditions in the brood pouch in situations of high temperatures and low oxygen levels enables this species to maintain a high reproductive output even under adverse and fluctuating environmental conditions.

Known Predators/Herbivores

It is eaten by fish such as Brown trout and some native gammarids such as Gammarus pulex. As all freshwater shrimps, it is also host to a range of parasites.

Resistant Stages

The species' ability to survive for a short time out of the water may have assisted its spread.

Habitat Occupied in GB

It inhabits rivers, canals, ponds, lochs, lakes and reservoirs, and can tolerate saline and/or poor quality water of low oxygen content. It is particularly common in shallow eutrophic waters, often occupying the most polluted areas of a river where no native Gammarus species can be found. Consequently, invasions by this species and subsequent replacement of native amphipods are frequently accompanied by environmental degradation.

The species is established in England, Wales and Scotland. It is also known from Northern Ireland and Ireland, and several other European countries including the Netherlands, Belgium, France and Germany.

Environmental Impact

Observations that it may replace native amphipod species (e.g. Gammarus pulex) have been reported from Loch Lomond and Loch Ness. However, evidence for co-existence with native amphipod species has also been reported from several other British freshwaters.

Health and Social Impact

None known.

Economic Impact

None known.

Identification

Gledhill, T., Sutcliffe, D.W. & Williams, W.D. (1993) British freshwater Malacostraca: a key with ecological notes. Freshwater Biological Association Scientific Publication, 52, 1-172.

Biology, ecology, spread, vectors

Crawford, G.I. (1937) An amphipod, Eucrangonyx gracilis S.I. Smith, new to Britain. Nature, 139, 327.

Dick, J.T.A., Faloon, S.E. & Elwood, R.W. (1998) Active brood care in an amphipod: influences of embryonic development, temperature and oxygen. Animal Behaviour, 56, 663-672.

Garland, E.M. (1981) The colonisation of Windermere by Crangonyx pseudogracilis (Crustacea, Amphipoda) 1961 to 1964. Freshwater Biology Association.

Holland, D.G. (1976) Distribution of Freshwater Malacostraca in Area of Mersey and Weaver River Authority. Freshwater Biology, 6, 265-276.

Hynes, H.B.N. (1955) Distribution of some freshwater Amphipoda in Britain. Verhandlungen der internationalen Vereinigung fuer Limnologie, 12, 620-238.

MacNeil, C., Dick, J.T.A. & Elwood, R.W. (2000) Differential physico-chemical tolerances of amphipod species revealed by field transplantations. Oecologia, 124, 1-7.

Management and impact

Conlan, K.E. (1994) Amphipod crustaceans and environmental disturbance: a review. Journal of Natural History, 28, 519-554.

MacNeil, C., Elwood, R.W. & Dick, J.T.A. (1999) Differential microdistributions and interspecific interactions in coexisting Gammarus and Crangonyx amphipods. Ecography, 22, 415-423.

General