Hemigrapsus

Pronunciation

How to pronounce Hemigrapsus: //ˌhɛmɪˈɡræpsəs//

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Summary

Hemigrapsus sanguineus, the Japanese shore crab, is an invasive species originating from East Asia. Notable for its morphological characteristics, it has spread to various regions, affecting local crab populations and ecosystems due to its opportunistic predatory behavior and adaptability.

Physical Characteristics

Squarish carapace, 2 inches (50 mm) wide, with three teeth along the forward sides; alternating light and dark bands on pereiopods; males have a bulb-like structure at the base of the movable finger on their claws; three spines on each side of the carapace. Adult sizes range from 35–42 mm in width.

Identification Tips

Look for three spines on each side of the carapace and alternating light and dark bands on the pereiopods. Males can be identified by the bulb-like structure at the base of the movable finger on their claws.

Habitat

Rocky shores interspersed with large rocks; can also inhabit oyster reefs and salt marshes.

Distribution

Native to coastal waters of the northwestern Pacific Ocean from Peter the Great Bay in southern Russia to Hong Kong. Introduced to North America (from New Jersey, 1988) and Europe (first reported in France in 1999) with sightings extending to the UK, Sweden, and Australia.

Diet

Opportunistic omnivore, primarily consuming small invertebrates such as mussels, snails, and amphipods. Shows a broad diet but prefers to eat other animals over algae.

Life Cycle

Females produce 3–4 broods per year with up to 50,000 eggs at a time. The eggs hatch into zoea larvae, progressing through four zoea stages and one megalopa stage within 16–25 days before settling into benthic adults after metamorphosis.

Reproduction

Females can produce multiple broods per year with thousands of eggs in each brood; eggs typically hatch in late summer or fall.

Predators

Native crustacean-eating fish and possibly other native crabs.

Ecosystem Role

As an invasive species, H. sanguineus may out-compete native crab species and alter local ecosystems, but also serves as a food source for native predators.

Tags

• crustacean
• invasive species
• Japanese shore crab
• Hemigrapsus sanguineus
• ecology