Carcinus maenas

Distinguished from the closely related Carcinus aestuarii by three undulations between the eyes that protrude beyond the eye margin (C. aestuarii lacks bumps and carapace extends forward smoothly). Male gonopods curve outward in C. maenas but are straight and parallel in C. aestuarii. Five short teeth behind each eye characteristic of C. maenas.

Carapace up to 60 mm long and 90 mm wide in native range, reaching 100 mm in some invaded areas. Carapace features five short teeth behind each eye and three distinct undulations between the eyes that protrude beyond the eye margin. Coloration highly variable: green, brown, grey, or red. Red coloration develops in individuals that delay moulting. Juveniles display greater patterning than adults.

Protected and semi-protected marine and estuarine habitats with mud, sand, or rock substrates; submerged aquatic vegetation; emergent marsh. Soft bottoms preferred. Cannot tolerate wave-swept open shores. Found in wave-protected sheltered bays, estuaries, and harbors. Euryhaline as adults (4–52 ‰ salinity); early life stages more restricted. Temperature tolerance 0–30 °C for adults; larvae require 12–27 °C.

Native: northeast Atlantic Ocean, Baltic Sea, European and North African coasts from Iceland and Central Norway southward, east to Baltic Sea. Introduced: Atlantic and Pacific coasts of North America (first observed Massachusetts 1817; California 1989), Australia (late 1800s), South Africa (1983), South America (Patagonia by 2003), Argentina (San Matías Gulf). Isolated appearances in Brazil, Panama, Hawaii, Madagascar, Red Sea, Pakistan, Sri Lanka, Myanmar without established populations.

Reproductive activity peaks May to July in some populations, but egg-bearing females present nearly year-round in recently established populations. Larvae develop offshore; juveniles settle in intertidal zone. Activity primarily diurnal but tide-dependent.

Omnivorous predator feeding on bivalve molluscs (clams, oysters, mussels—up to 40 clams per day), polychaete worms, and small crustaceans including conspecifics up to own size. Soft-shell clam (Mya arenaria) preferred prey. Preys on young of bivalves and fish. Feeding rates reduced in colder water.

Females produce over 400,000 eggs. Larval development occurs offshore in multiple stages before final moult to juvenile in intertidal zone. Young crabs inhabit seaweeds and seagrasses until adulthood. Extended reproductive period with nearly year-round egg-bearing females observed in some invaded populations.

Primarily diurnal with activity modulated by tides; can be active at any time. Uses habitat-specific camouflage: mudflat crabs match substrate color, rock pool crabs use disruptive coloration. Red color morph individuals more aggressive and dominant in contests over food, but less tolerant of low salinity and hypoxia. Higher temperatures disrupt established dominance hierarchies based on size and color morph.

Predator with documented impacts on native bivalve populations, including decline of native clams (Nutricola spp.) in California and destruction of soft-shell clam fisheries in eastern North America. Competes with native crabs for resources and shelter. Consumes Zostera marina, affecting habitat for Dungeness crab and juvenile salmon. Preys on young of commercially important species including oysters and Dungeness crab.

Major economic and ecological threat as invasive species; implicated in fisheries declines and habitat damage. Subject to control efforts including trapping and bounties. Small-scale fishery in native range (~1200 tonnes annually, mainly France and UK). Culinary use in native range for soups and sauces; soft-shell preparation adapted from Mediterranean methods in New England. Experimental products include green crab stock, empanadas, patties, and distilled spirits. Genome sequenced 2025 for invasion biology research.

• Carcinus aestuariiMediterranean green crab; distinguished by smooth carapace lacking undulations between eyes, and straight parallel male gonopods versus curved gonopods in C. maenas. Also invasive in some regions.
• Hemigrapsus oregonensisNative Pacific shore crab; competes with C. maenas for shelter on west coast of North America.
• Callinectes sapidusNative blue crab in eastern North America; appears to limit C. maenas populations through predation or competition, with negative correlation between species abundances.

• invasive species
• marine crab
• estuarine
• predator
• fisheries pest
• phenotypic plasticity
• global invader

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• PopulationDynamics of Green Crabs (Carcinus maenas) -- A Review
• Figure 2: Standard agonistic behaviors of the shore crab Carcinus maenas .
• PopulationDynamics of Green Crabs (Carcinus maenas) -- A Review
• Supplemental Information 2: Tissue distribution of neuropeptides and neuropeptide GPCRs in various tissues of Carcinus maenas .
• Fluctuations in native and invasive populations of the European green crab, Carcinus maenas: Habitat preferences, diet, and ecological interactions
• Moving northwards: Invasive Green Crab ( Carcinus maenas ) Expands into the Southwestern Atlantic
• Alteration of camouflage and behaviour in two marine invertebrates, Sepia officinalis and Carcinus maenas, by antidepressant medication
• Behaviour of Sacculinized Shore Crabs (Carcinus maenas Pennant)
• Figure 1: Global distribution of European green crab ( Carcinus maenas ) and sampling locations for green crab populations used in this study.