Green crabs are an invasive species native to regions of Western Europe and Africa. What’s an invasive species you ask? The National Oceanic and Atmospheric Association defines an invasive species as “an organism that causes ecological or economic harm in a new environment where it is not native”.

Green crabs are commonly considered one of the “world’s worst invasive species” and their populations and range are expected to increase with climate change. As of today, the crab has successfully invaded every continent except Antarctica.

Introduction: Green crabs were likely transported from Europe in the ballasts of ships, arriving in eastern North America in the mid 1800s. However, in the late 20th century these eastern populations began to flourish and soon researchers began finding the crab in Japan, western North America, and southern Australia, Africa, and South America. With a larval life cycle, baby green crabs can drift considerable distances from the parent’s population, allowing the species to quickly establish in new territory. Modern shipping practices have exacerbated their spread and populations will likely increase with climate change.

Biology: Considering a single female green crab can produce 185,000 eggs in a single year, populations can expand rapidly and early detection is key. The crab can live up to seven years and tolerates a wide range of salinities and temperatures.

Green crabs have the potential to destroy some of the world’s most vulnerable ecosystems and valuable fisheries:

Shellfish: Green crabs eat a wide variety of shellfish, preying on oyster, clam, mussel, lobster, and crab populations across the world. Since the late 20th century, green crabs have decimated New England soft-shell clam, mussel, and oyster populations. A single green crab can eat over 40 juvenile soft-shell clams in a single day.

Eelgrass: While foraging for food green crabs “slice” through eelgrass, destroying the plant. Eelgrass provides nursery habitat for juvenile fish and shellfish and in turn serves as a feeding ground for many migratory bird species and sea turtles.

Lobsters & Native Crab: Green crabs compete with native crab and lobster populations for food and shelter. As a ferocious predator, green crabs have also been known to eat juvenile lobster and crab.

Despite their name, green crabs come in all colors of the rainbow and can be multi-hued. If you see a crab with “five points” on each side of the face, it’s likely a green crab.

Green crabs can be found pretty much anywhere along the coast of New England: from tide pools, to salt-marshes, to even scuttling across the beach.

Additional Resources:

Seadrift Lagoon Green Crab Project

Washington Sea Grant Green Crab Team

Eat the Invaders

References:

Agonistic interactions between the invasive green crab, Carcinus maenas (Linnaeus) and juvenile American lobster, Homarus americanus

A global invader at home: population structure of the green crab, Carcinus maenas, in Europe

Introduction, dispersal and potential impacts of the green crab Carcinus maenas in San Francisco Bay, California

Predicting the impact of introduced marine species: Lessons from the multiple invasions of the European green crab Carcinus maenas

Spread and potential impact of the recently introduced European green crab, Carcinus maenas, in central California

‘Highly Aggressive’ Green Crabs From Canada Menace Maine’s Coast