Caprella mutica

Reliably distinguished from similar species by setose first and second pereonites in males (smooth in Caprella acanthogaster) and elongated oval gill shape (linear in C. acanthogaster). Males exhibit considerable morphological variation.

Shallow protected marine waters, infralittoral and littoral zones to 0.7–13 m depth. Native populations on floating macroalgae (Sargassum, Laminaria, etc.), hydrozoans, bryozoans, marine plants. Introduced populations predominantly synanthropic on artificial structures: submerged ropes, fishing nets, pilings, docks, buoys, aquaculture equipment, oil platforms, ship hulls, offshore wind farms. Poor swimmer; clings to substrates in upright posture, moving by undulating inchworm-like locomotion using posterior pereopods and gnathopods.

Native: Sea of Japan (Peter the Great Gulf, Primorsky Krai, Russia; Hokkaido and surrounding regions, Japan). Introduced: North America (west coast from California to Alaska, British Columbia; east coast from Connecticut to Maine, New Brunswick, Quebec), Europe (Netherlands, Belgium, Norway, Germany, Scotland, England, Wales, Ireland, France, Denmark), New Zealand (Timaru, Lyttelton, Marlborough Sounds, Wellington Harbour), South America (northern Chile, Coquimbo, with predicted expansion southward).

Reproduces year-round with peak in summer months (March–July). Populations peak August–September, declining sharply in winter.

Omnivorous opportunistic feeder with flexible feeding modes: detritivore, grazer, scavenger, filter feeder, predator. Captures particles by waving body with antennae extended, using comb-like setae on second antennae; scrapes food with antennae; strikes prey with large gnathopods. Diet includes algae (planktonic and macroalgae), dinoflagellates, hydrozoans, bryozoans, diatoms, copepods, brine shrimps, other amphipods, suspended organic particles, fish feed, decaying organic matter; engages in cannibalism on dead or dying conspecifics.

Direct development without planktonic larval stage; hatchlings resemble miniature adults. Juveniles emerge from brood pouch at 1.3–1.8 mm, moult at 5.0–11.0 day intervals. Sexual differentiation at fifth instar; maturity at seventh instar (21–46 days post-hatching, up to six months in late summer wild populations). Females produce first brood at Instar VII at ~8.5 mm body length, average two sequential broods at 20.2 day intervals; brood size increases from ~11 to ~26 hatchlings, maximum 82. Eggs incubated 30–40 days in brood pouch. Laboratory lifespan: males 68.8 days, females 82 days.

Males highly aggressive; engage in 'boxing matches' using second gnathopods with lethal outcomes possible; compete for access to females. Males detect female moult status by antennal contact; amplexus lasts 10–15 minutes, followed by brief male defense period. Females become aggressive post-mating, driving off males and protecting brood. Reluctant to release substrate grip; changes color to match environment (mechanism unknown).

Prey for fish, crabs, nudibranchs, starfish, nemertean worms, sea anemones, hydrozoans; provides link between plankton and larger predators. High polyunsaturated fatty acid and carotenoid content makes valuable food source. Invasive populations compete aggressively with native caprellids, displacing species such as Caprella linearis and Pseudoprotella phasma from limited habitat; may alter native community structure through competition and predation.

Major biofouling organism on aquaculture equipment, ship hulls, and marine infrastructure; potential economic costs from removal. Accidentally introduced globally through shipping ballast water, hull fouling, and oyster aquaculture (particularly with Pacific oyster Crassostrea gigas shipments). Investigated as potential marine fish feed resource due to rapid growth and nutritional value. No effective control measures known; management focuses on native species preservation rather than eradication.

• Caprella acanthogasterNative to East Asian waters; distinguished by smooth (not setose) first and second pereonites and linear (not oval) gill shape; C. mutica was initially misidentified as this species
• Caprella linearisNative European caprellid; smaller and competitively inferior; displaced by C. mutica in laboratory and field conditions in the North Sea
• Pseudoprotella phasmaNative European caprellid; ecologically similar; displaced from artificial habitat patches by C. mutica in competition experiments

• invasive species
• marine amphipod
• skeleton shrimp
• biofouling
• sexual dimorphism
• global spread
• competition
• aquaculture pest

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• longhorned beetles | Beetles In The Bush | Page 10
• On the path to cosmopolitanism: the continuing geographic expansion of Caprella mutica (Crustacea, Amphipoda)
• Mitochondrial DNA reveals multiple Northern Hemisphere introductions of Caprella mutica (Crustacea, Amphipoda)
• Survivorship, growth and reproduction of the non-native Caprella mutica Schurin, 1935 (Crustacea: Amphipoda)
• Distribution of the invasive Caprella mutica Schurin, 1935 and native Caprella linearis (Linnaeus, 1767) on artificial hard substrates in the North Sea: separation by habitat
• Rearing Method for Caprella Mutica (Malacostraca: Amphipoda) in an Exhibition Tank in the Port of Nagoya Public Aquarium, with Notes on Reproductive Biology
• Caprella mutica in the Southern Hemisphere: Atlantic origins distribution, and reproduction of an alien marine amphipod in New Zealand
• Competition between the non-native amphipod Caprella mutica and two native species of caprellids Pseudoprotella phasma and Caprella linearis
• Seasonal population dynamics of the non-native Caprella mutica (Crustacea, Amphipoda) on the west coast of Scotland
• Environmental tolerance of Caprella mutica: Implications for its distribution as a marine non-native species
• Distribution of the introduced amphipod, Caprella mutica Schurin, 1935 (Amphipoda: Caprellida: Caprellidae) on the west coast of Scotland and a review of its global distribution