The Dungeness crab (Metacarcinus magister) is a large marine crustacean of significant ecological and economic importance along the Pacific Coast of North America. Its range extends from Alaska down to Santa Barbara, California, inhabiting sandy and muddy bottoms from the intertidal zone to subtidal depths. This species functions both as a predator and an opportunistic scavenger within the benthic community. The crab’s highly diverse dietary habits reflect its adaptability and ability to consume a broad spectrum of available food sources.
Primary Prey and Preferred Food Sources
The Dungeness crab’s diet is highly generalized, but gut content analyses show that certain benthic organisms form the bulk of its meals. Bivalves, such as small clams and mussels, are primary prey items across the crab’s range and life stages. The crab often finds these organisms buried within the sediment, relying on foraging behavior to unearth them.
The diet also includes a variety of smaller crustaceans, specifically shrimp, amphipods, and isopods. Marine worms, particularly polychaetes, are readily consumed when encountered in the substrate.
Dungeness crabs also feed on other invertebrates, including sand dollars and brittle stars. They consume small fish, especially those that are slow-moving or bottom-dwelling. This broad menu highlights the crab’s capacity to exert predatory pressure on multiple levels of the seafloor community.
Feeding Habits and Consumption Strategies
Dungeness crabs locate their meals primarily through chemoreception, using a strong sense of smell and chemical detection to find both live and dead organisms. They are active foragers, searching the substrate and probing the sand and mud with their chelae (claws) to detect buried items. This search behavior allows them to uncover bivalves and worms.
Once prey is secured, the crab uses its powerful, heavy pinching claws to process the food. For hard-shelled organisms like clams, the crab may chip away at the shell or use the force of its claws to crush it entirely. Smaller feeding appendages pass the fragments into the mouth, where they are processed by tooth-like structures in the gastric mill.
The crab is also a capable scavenger, consuming carrion such as dead fish or discarded materials, which supplements its actively hunted diet. Cannibalism, particularly of recently molted or smaller conspecifics, is another consumption strategy observed across all age groups.
Dietary Shifts Between Juvenile and Adult Crabs
The diet of the Dungeness crab changes noticeably as it grows from juvenile to adult, reflecting differences in size, habitat, and physical capability. Juvenile crabs often inhabit sheltered areas like eelgrass beds and estuaries, where they feed on smaller, softer-bodied prey. First-year crabs primarily consume very small bivalves and tiny crustaceans, including their own species.
As the crabs mature, their diet expands to include larger prey, such as various species of shrimp and small fish. This shift may help reduce competition and cannibalism between different age cohorts.
Adult crabs possess much larger and stronger claws, allowing them to tackle harder-shelled and bulkier prey inaccessible to juveniles. The adult diet includes substantial quantities of larger bivalves, crabs, and fish. This progression from small, soft prey to large, hard-shelled organisms reflects a move from the resource-limited estuarine nursery to the richer, deeper subtidal habitats.