Crabs

Crabs are crustaceans within the order Decapoda, and they encompass a diverse group of species characterized by a broad, usually oval carapace and two large front claws. Most crabs are aquatic, inhabiting oceans, seas, estuaries, and coastal wetlands, though some species spend portions of their lives in freshwater or brackish habitats. They typically have a hard exoskeleton and a flexible abdomen tucked beneath the thorax; they grow by molting.

Crabs vary greatly in size and form, from small fiddler crabs with a single enlarged claw to large commercial species such as the blue crab, Dungeness crab, and king crabs. They occupy a wide range of environments, including sandy shores, mud flats, seagrass beds, reefs, and mangroves. Many are burrowers or walkers, and some have adapted to swimming with flattened hind legs.

Ecology and behavior: Crabs are omnivorous scavengers and opportunistic feeders, consuming detritus, algae, invertebrates, and small fish. They often play important ecological roles as predators and prey, and many species are active at night. Reproduction involves females brooding fertilized eggs under their abdomen; after several developmental stages in the larval phase, the young crabs emerge as juveniles and gradually reach adult form.

Human use and conservation: Crabs are commercially important in many regions, with species such as the blue crab and Dungeness crab harvested for food. Harvests are managed through size limits, quotas, seasonal closures, and habitat protection to maintain populations, though overexploitation, habitat degradation, and climate change pose ongoing threats to some species.