Carcinus maenas

This crab lives in the sea.

It can be green, brown, or even red. Red crabs are very strong.

These crabs love to eat. They eat worms and small clams. One crab can eat 40 clams in one day!

This crab moves to new lands. It can hide on big ships. It can also ride on seaweed.

It can live in very cold water. It can also live where the water is not very salty.

These crabs are found in many places. They are now in places like America and Australia. They are very good at finding new homes.

The European green crab is a tough animal. It is native to Europe and North Africa.

These crabs come in many colors. They can be green, brown, grey, or red. Red crabs are very strong and aggressive. However, they do not like water that is not very salty.

This crab is a great traveler. It can move to new places by hiding on ships. It can also ride on seaweed or move with ocean currents. Because of this, it is an invasive species. An invasive species is an animal that moves into a new area and can cause problems.

Green crabs love to eat. They eat worms and small creatures. They also eat clams. One crab can eat up to 40 clams in one day! This can hurt local fishing. They eat many young clams and oysters.

In some places, people try to stop them. Some crabs use camouflage to hide. They match the color of the mud or rocks. This helps them stay safe from predators.

The European green crab is a very hardy living thing. It is native to the North-east Atlantic Ocean and the Baltic Sea. It also comes from the coasts of North Africa.

These crabs are famous for being a widespread invasive species. This means they move into new places where they do not belong. They are even listed among the 100 worst invasive species in the world.

Because they are so good at moving, they can change entire ocean habitats.

These crabs have many ways to travel to new homes. They can hitch a ride on the hulls of large ships. They might hide in packing materials like seaweed used for shipping. They can even move by riding on ocean currents as larvae.

Once they arrive, they find many places to live. They like soft bottoms made of mud, sand, or rock. They are also euryhaline, which means they can live in water with different salt levels. This helps them survive in estuaries where the salt level changes.

Scientists have studied these crabs for a long time. The first time they were seen in North America was in Massachusetts in 1817. They spread very fast along the Pacific Coast later on. In 1993, they began to expand their range in California. By 1999, they had reached all the way to British Columbia.

In 2025, scientists even mapped their complete genome. This helps researchers understand how they are so successful at invading new lands.

There are many specific facts about how they look and act. A crab's shell, called a carapace, can be up to 80 millimeters wide.

Their color can be green, brown, grey, or even red. Red crabs are often stronger and more aggressive than green ones.

They are also very hungry predators. One single crab can eat up to 40 clams in just one day.

This eating can hurt local fisheries by taking food from other animals.

Learning about these crabs helps us understand how nature stays in balance. In some places, native crabs like the blue crab help control them.

Other animals, like native rock crabs, also try to eat them. People also try to help by trapping the crabs to keep their numbers down.

Even though they are hard to stop, humans work to protect local sea life. Understanding these small creatures helps us protect the big oceans we all share.

The European green crab, known scientifically as *Carcinus maenas*, is a highly successful marine crustacean. It is native to the North-east Atlantic Ocean and the Baltic Sea, as well as the coasts of North Africa.

While it is a common part of its home ecosystem, it is also recognized as one of the world's 100 worst invasive alien species. This means that when it moves into new environments, it can cause significant damage to local wildlife and industries. Because it can survive in so many different places, it has become a global concern for marine biologists and fisheries managers alike.

To understand why this crab is such a successful invader, we must look at its biology. The crab possesses a hard shell called a carapace, which can reach a width of 80 millimeters.

A key feature of its anatomy is the presence of five short teeth along the rim of the carapace behind each eye. Additionally, there are three undulations, or bumps, located between the eyes. These bumps are a vital way for scientists to distinguish *C. maenas* from a similar species, *Carcinus aestuarii*. In *C. aestuarii*, the carapace lacks these bumps and extends further forward past the eyes.

The color of the crab is not always green, despite its common name. It can appear in shades of brown, grey, or red. This color variation is partly due to genetics, but local environmental factors play a massive role. For instance, crabs that delay the process of moulting, or shedding their old shells, often become red. These red individuals tend to be stronger and more aggressive than their green counterparts. However, they are also less able to tolerate environmental stresses like hypoxia, which is a lack of oxygen, or low salinity.

*Carcinus maenas* is also an incredibly hardy animal due to its euryhaline nature. This term means it can tolerate a wide range of salinity, from 4 to 52 parts per thousand. This allows the crab to thrive in estuaries, where fresh water and salt water mix. It can also survive a wide range of temperatures, allowing it to live in very cold climates under winter ice.

The crabs spread to new locations through several mechanisms. They can hitch rides on ship hulls or hide in seaweed used as packing material. They also move via ocean currents as larvae or by being transported in bivalves used for aquaculture.

The history of its invasion shows how rapidly it can move. It was first observed on the east coast of North America in Massachusetts in 1817. On the Pacific Coast, the species was found in San Francisco Bay in 1989. It began a rapid northward expansion in 1993, reaching British Columbia by 1999. This allowed the species to extend its total range by 1,000 kilometers in just ten years.

In Australia, it was likely introduced as early as the 1850s and has since spread across many coastal regions.

As a predator, the green crab has a massive impact on marine food webs. It is a diurnal hunter, meaning it is mostly active during the day, though its activity also follows the tides. The crab eats a variety of organisms, including worms, small crustaceans, and many types of mollusks. A single crab can eat up to 40 clams in one day.

This voracious appetite can devastate local fisheries. For example, it preys heavily on soft-shell clams, scallops, and northern quahogs. It can even compete with native Dungeness crabs for food and habitat.

Efforts to control these populations vary by location. In some areas, native species provide natural checks. In eastern North America, the native blue crab can help control green crab numbers. On the West Coast, native rock crabs, such as *Cancer productus*, also prey on them.

Humans also use active methods, such as trapping or declaring disasters to request emergency funding. Scientists have even studied the parasitic barnacle *Sacculina carcini* as a potential biological control. However, using such a parasite is risky because it might also infect native species like the Dungeness crab.