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Rock Crab

Cancer irroratus

The rock crab is a hardy crustacean commonly found in shallow waters along the North Atlantic coasts, particularly in bays with sandy or muddy bottoms, as well as along rocky slopes and ledges. With its broad, reddish-brown carapace covered in fine granules, the rock crab blends seamlessly into its surroundings, making it well-suited for life in rocky and intertidal zones.

Rock crabs are opportunistic feeders, using their powerful, yet slow-moving, front claws to capture live prey such as mussels, barnacles, smaller crabs, and marine worms. They are also known scavengers, feeding on dead animals that they find along the seafloor. Their strong claws are ideal for breaking open hard-shelled prey, but their size and weight can make them less nimble than other crab species.

As with all crabs, the rock crab must molt its exoskeleton as it grows, a process known as moulting. This occurs because a crab’s hard outer shell does not expand, so it must shed it and grow a new, larger one. For female rock crabs, this typically happens in the fall, ensuring they are soft-shelled and vulnerable during mating. Males, on the other hand, molt during the winter months after mating, providing protection to the female while she is still soft. After mating, the female carries fertilized eggs under her abdomen for almost a year before they hatch. In the fall, you might spot the females carrying bright orange-red eggs, a beautiful sight that marks the ongoing life cycle of these crabs.

Fun Fact!

Rock crabs’ slow and powerful claws are an interesting adaptation for their feeding and defense. The larger claw is particularly useful for capturing and manipulating prey, while the smaller claw plays a more delicate role in tasks like grooming. Additionally, their molting process ensures they can continue to grow and protect themselves throughout their life.

Habitat & Range

Rock crabs are found in the shallow waters of the North Atlantic, particularly in bays with sandy or muddy bottoms, and along rocky shores and ledges. They thrive in colder, northern habitats where they can find plenty of shelter.

Lifespan & Growth

Rock crabs can live for 3-5 years, growing to a carapace width of up to 15 cm. They molt several times as they grow, shedding their exoskeletons and gradually increasing in size.

Role in Ecosystem

As both predators and scavengers, rock crabs play a vital role in recycling nutrients in the marine ecosystem. They help control populations of smaller invertebrates and provide food for larger marine predators, including fish, seabirds, and other crustaceans.

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