The Wide-Ranging Diet of Crabs: A Look at What These Crustaceans Love to Eat

With over 6500 species spanning aquatic environments across the globe crabs comprise an extremely diverse group of crustaceans. Their habitats range from the deep ocean floor to intertidal zones to freshwater rivers and streams. With such diversity comes an equally diverse crab diet. While crabs are largely opportunistic omnivores, different species have adapted to feast on a wide array of food sources.

Small Fish and Crustaceans

Many crabs are adept at hunting down smaller marine animals to satisfy their primarily carnivorous diets Species like blue crabs, snow crabs, and king crabs eagerly consume small fish when the opportunity arises. Usually slow moving, crabs rely on their strong pincers and keen sense of smell to capture unsuspecting fish on the seafloor Crabs also feed on other, smaller crustaceans like shrimp, krill, crayfish, and juvenile crabs. The abundant protein and essential nutrients in marine animal flesh aid growth and reproduction in crabs.

Carrion and Decaying Matter

In addition to active hunting, crabs play an important role as scavengers in their ecosystems. Using specialized sensory organs, crabs can detect chemicals released by decaying animals. They flock to carrion to pick apart the remains of fish, whales, and other dead sea creatures. Crabs are able to utilize nutrients from aging organic matter that may be unpalatable to other species. Their diverse diet of both live prey and detritus helps recycle nutrients back into the food chain.

Algae and Plant Matter

While most recognized as predators and scavengers, some crab species have a more herbivorous diet. Terrestrial crabs in tropical climates often feed on leaf litter and fallen fruit. Marine crabs like fiddler crabs consume algae, marsh grass, and other aquatic plants. Algae provides crabs with fiber, minerals, and essential fatty acids. Many crabs change their diet preferences as they develop, relying more on plant matter as juveniles before adopting a more carnivorous adult diet.

A Diet Dictated by Size and Habitat

Crabs inhabit environments from the deep sea to intertidal zones to land, so diet varies enormously based on habitat and food availability. Tiny pea crabs measure just a few millimeters across, dining on similarly sized zooplankton and phytoplankton. Giant spider crabs and Japanese spider crabs have leg spans over 10 feet, capable of capturing large fish and other sizable prey. Deep sea king crabs subsist on whatever food particles drift down to their inhospitable environment miles underwater.

A crab’s diet also depends heavily on its size and life stage. Minute larvae survive on algae, plankton, and particulate organic matter. Once crabs molt into their juvenile form, they transition to larger prey like worms, smaller crustaceans, and mollusks. As crabs grow in size, their diet expands to include more substantial sources of protein like fish, carrion, and vegetation.

Hunting Strategies

Crabs employ an array of tactics to hunt down food. With poor eyesight, most rely on their highly sensitive sense of smell to locate prey. Crabs use antennae and mouthparts to detect chemicals that signal food is near. Species like coconut crabs and land hermit crabs will also rely on touch, tasting the air to identify scents.

Other crabs are more active hunters, creeping along the seafloor feeling for hidden animals with their walking legs. Large species can use their oversized claws to capture and crush prey. Tiny pea crabs will stealthily pick at leftovers from the meals of larger animals.

Regardless of their diverse habitats and characteristics, all crabs are resourceful feeders, using their environmental adaptations to take advantage of any nutrients they can find. Their flexible eating habits and ability to consume a wide variety of food sources have allowed crabs to thrive in aquatic and terrestrial environments across the globe.