Crustaceans, including crabs, shrimp, lobsters, and krill, are defined by their tough, multi-layered exoskeleton. This hard outer shell, composed of chitin and reinforced with calcium salts, functions as both armor and structural support. Despite this defense, these arthropods occupy a central position in global marine and freshwater ecosystems, serving as a high-energy food source for many animals. Accessing the meat inside the shell has driven the evolution of specialized hunting strategies across nearly every class of aquatic and coastal predator.
Primary Aquatic Threats: Predation by Fish
Fish represent the largest and most diverse group of crustacean predators, developing specialized mouthparts and feeding behaviors. Small, planktonic crustaceans, such as copepods and krill, are consumed through massive-scale filtration by species like whale sharks. These tiny organisms are often the primary herbivores in the ocean.
Other fish have evolved powerful crushing jaws to break through the calcified shells of larger prey. Pufferfish possess robust, beak-like dental plates strong enough to crack open hard-shelled crabs and snails. Similarly, triggerfish employ formidable dentition to consume crustaceans and will use jets of water to uncover buried benthic prey.
Suction feeders, such as groupers, rely on stealth and rapid mouth expansion. They generate a vacuum-like force that pulls the prey directly into their throats, where heavy crushing tooth plates process the meal. Bottom-dwelling sharks and rays also consume crustaceans, with species like the cownose ray using specialized dental batteries to grind up hard-shelled invertebrates.
Specialized Shell-Crushers: Marine Mammals and Reptiles
Vertebrates that spend their lives in the water have developed unique anatomical features or techniques to overcome the crustacean’s armor. Baleen whales sustain themselves almost entirely on krill, which are small, shrimp-like crustaceans. These whales gulp enormous volumes of water and push it out through fringed baleen plates, which act like a sieve to trap the dense swarms of planktonic prey.
Among marine mammals, the walrus is an example of specialized benthic feeding. Walruses forage on the seafloor, using sensitive vibrissae to locate buried crustaceans. They use a powerful suction mechanism, rapidly pulling their tongue back to suck the soft parts of the prey directly out of the shell.
Marine reptiles also participate in this predatory guild, most notably sea turtles. The loggerhead sea turtle has powerful jaw muscles and a beak-like jaw structure adapted for crushing the shells of crabs, conchs, and other hard-shelled prey. Their diet depends heavily on the crustaceans and mollusks they encounter on the ocean floor.
Coastal and Aerial Hunters: Birds and Amphibious Mammals
The intertidal zone, where crustaceans are exposed by the ebb and flow of tides, is exploited by aerial and amphibious predators. Shorebirds, such as sandpipers and plovers, have long, thin bills they use to probe deep into mudflats and sand. They extract small, burrowing crustaceans like amphipods and ghost shrimp, relying on tactile sensation to locate hidden prey.
Larger avian predators, including gulls and herons, use forceful methods. Gulls carry large crabs or shellfish high into the air and drop them onto hard surfaces to crack the shell and access the meat inside. Herons and egrets patrol the shallows, using sharp bills to stab at crabs and shrimp.
Amphibious mammals also target this resource, particularly crab species found along coastlines and riverbanks. Raccoons and foxes are opportunistic foragers that hunt crabs in the intertidal zone, often using their paws to flip them over and attack the softer underside. Coastal bear populations, such as brown bears, consume crabs and other shellfish as part of their diet.
The Internal Threat: Invertebrate Predators
Predation on crustaceans is not limited to vertebrates; it is extensive within the invertebrate community. Cephalopods, including octopuses and cuttlefish, are effective hunters of crabs and shrimp. The octopus uses its flexible body to sneak into crevices, often employing the webbing between its arms to trap the prey underneath.
A major threat comes from within the crustacean group, as larger species frequently prey on smaller ones, exhibiting cannibalism. A large crab will readily attack a smaller crab or an individual vulnerable after molting, when its new exoskeleton has not yet hardened. The powerful raptorial appendages of the mantis shrimp are also used to dispatch other crustaceans with a high-velocity strike.
Even echinoderms, like sea stars, are predators of crustaceans. Sea stars move over the seafloor using hundreds of tube feet, which they use to hold fast to prey. Some species consume slow-moving or immobilized crustaceans as part of their benthic diet.