Short description of Caprella mutica, Japanese skeleton shrimp

A large skeleton shrimp up to 49 mm in length; males are larger than females.  There are fine hairs on the first two body segments, large spines on third to seventh body segments in males and orange spots on the females’ brood pouch.

Impact summary: Caprella mutica, Japanese skeleton shrimp

An aggressive species, the Japanese skeleton shrimp may outcompete native skeleton shrimps for food and space, even at low densities.  On the west coast of Scotland, their abundance can reach 300,000 individuals m ^-2. Research suggests the potential for significant impacts on benthic communities. 

Habitat summary: Caprella mutica, Japanese skeleton shrimp

Typically found on a range of natural substrata including hydroids and attached or drifting macro-algae (seaweed), and also artificial substrata such as ropes, buoys, boat hulls and floating pontoons.  Often found associated with areas of human activity; marinas, harbours, aquaculture sites.

Overview table

Environment	Marine
Species status	Non-Native
Native range	China, Mongolia, Hokkaido, Honshu, Kyushu, Nansei-shoto, Shikoku, North Korea, South Korea, Sakhalin, Taiwan
Functional type	Detritivore
Status in England	Non-Native
Status in Scotland	Non-Native
Status in Wales	Non-Native
Location of first record	Lyne of Lorn, near Oban Scotland
Date of first record	2000

Origin

Native to the sub-boreal waters of North-East Asia.  The Japanese skeleton shrimp was first described from Peter the Great Bay, on the Siberian coast of the Sea of Japan in 1935.

First Record

First recorded in the UK in 2000, from a salmon farm near Oban in Scotland.  It is not known how long the Japanese skeleton shrimp had been present at the site prior to identification. 

Pathway and Method

The method of introduction to GB is unknown but is likely to be associated with shipping and aquaculture.  The Japanese skeleton shrimp commonly attaches to algae which in turn are regularly found attached to ships’ hulls. It has also been recorded in ships’ sea chests (the intake area for ballast water), living among colonies of hydroids.  Transport within ballast water or associated with aquaculture products and equipment such as fish farm cages, nets and buoys may also occur. 

Species Status

A rapidly invading species; within 40 years the Japanese skeleton shrimp has spread throughout the Northern hemisphere and has recently been found in New Zealand.    In the UK, its range has extended throughout the North Sea and Celtic Sea coasts and the English Channel in less than 14 years.  Established non-native populations are now found on both coasts of North America, Western Europe and New Zealand. 

Dispersal Mechanisms

Lacking a free swimming planktonic stage the Japanese skeleton shrimp spends its entire life on the substrate surface.  Consequently this species naturally has a limited dispersal potential, typically only a few kilometers per year.  This characteristic is an impediment to natural global dispersal, supporting the theory that introductions are associated with human activity.  On a local and regional scale, dispersal along coasts occurs on drifting algae.

Reproduction

The Japanese skeleton shrimp has a high reproductive capability.  Females produce multiple broods and large brood sizes; the maximum number of hatchlings recorded per female being 82.  The first brood is produced approximately 53 days after hatching at an average body length of 8.5 mm and at a water temperature of 13-14 °C. 

Known Predators/Herbivores

A variety of fish and crabs prey upon the Japanese skeleton shrimp.   

Resistant Stages

None known.

Habitat Occupied in GB

The Japanese skeleton shrimp has been found in high concentrations in marine Special Areas of Conservation (SACs) designated for their biogenic reefs.  It tends to be found in areas of human activity on natural and artificial substrata including hydroids, macro-algae, mooring ropes and buoys, but has yet to be found in natural habitats. 

Native to sub-boreal waters of North-East Asia.  Now widely distributed within the Northern hemisphere and recently found in New Zealand.  In GB the Japanese skeleton shrimp has been recorded from southern and south west England, the west coast of Scotland and the Western Isles.

Environmental Impact

In aquarium trials the Japanese skeleton shrimp has displayed aggressive competitive behavior, displacing native skeleton shrimps from the substrate even at low densities.  While this behavior has not been observed in the wild, Japanese skeleton shrimps have been recorded living in close proximity to native shrimps under the same environmental conditions, suggesting that similar situations may arise.  The wider environmental implications have yet to be confirmed, but it is possible that it will have a significant impact on benthic communities.

Health and Social Impact

None known.

Economic Impact

In the summer months, high densities of Japanese skeleton shrimp have been known to block water intakes on pumps for the feeding systems at caged fish sites and have settled on mussel lines which should have been covered with juvenile mussels.  Economic costs associated with removal of fouling organisms and loss of utility may be incurred.

Identification

Cook, E.J., Jahnke, M., Kerckhof, F., Faasse, M., Boos, K. & Ashton, G. (2007) European expansion of the introduced amphipod Caprella mutica Schurin 1935.  Aquatic Invasions, 2, (4), 411-421.

Oakley, J.  (2006) Caprella mutica. Japanese skeleton shrimp. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. Available from: http://www.marlin.ac.uk/speciesinformation.php?speciesID=2879

Biology, ecology, spread, vectors

Cook, E.J., Jahnke, M., Kerckhof, F., Faasse, M., Boos, K. & Ashton, G. (2007) European expansion of the introduced amphipod Caprella mutica Schurin 1935.  Aquatic Invasions, 2, (4), 411-421.

Frey, M.A., Gartner, H.N., Clarke Murray, C. & Therriault, T.W. (2009) First confirmed records of the non-native amphipod Caprella mutica (Schurin 1935) along the coast of British Columbia, Canada, and the potential for secondary spread via hull fouling. Aquatic Invasions, 4, (3), 495-499.

Shucksmith, R., Cook, E.J., Hughes, D.J. & Burrows, M.T. (2009) Competition between the non-native amphipod Caprella mutica and two native species of caprellids Pseudoprotella phasma and Caprella linearis. Journal of the Marine Biological Association of the United Kingdom, 89, (6), 1125–1132.

Willis, K.J., Cook, E.J., Lozano-Fernandez, M. & Takeuchio, I. (2004) First record of the alien caprellid amphipod, Caprella mutica, for the UK.  Journal of the Marine Biological Association of the United Kingdom, 84, 1027-1028.

Management and impact

Cook, E.J., Jahnke, M., Kerckhof, F., Faasse, M., Boos, K. & Ashton, G. (2007) European expansion of the introduced amphipod Caprella mutica Schurin 1935.  Aquatic Invasions, 2, (4), 411-421.

General

Ashton. G.V. (2006) Distribution and dispersal of the non-native caprellid amphipod, Caprella mutica Schurin, 1935.  Scottish Association for Marine Science [online] Available from: http://www.researchrepository.uhi.ac.uk/bitstream/10215/229/1/Gail%20Ashton%20thesis%20with%20consent.pdf

Schϋckel, U., Schϋckel, S., Beck, M. & Liebezeit, G. (2010) New range expansion of Caprella mutica Schurin, 1935 (Malacostraca: Caprellidae) to the German coast, North Sea.  Aquatic Invasions, 5, Supplement 1. S85-S89.