The marine world is filled with organisms that have developed hard outer coverings for protection, commonly referred to as shellfish, which include mollusks and crustaceans. This heavy armor, however, does not make them immune to predation. The high nutritional content locked inside these shells has driven an evolutionary arms race, resulting in a diverse group of predators that have developed highly specialized tools and techniques to access this food source. These methods range from brute mechanical force to chemical dissolution and even sophisticated tool use.
Shell Crushers: Specialized Fish and Crustaceans
Some of the ocean’s most effective shell predators rely on sheer physical power and specialized anatomy to break through hard casings. Certain fish species are masters of this “durophagy,” the consumption of hard-shelled organisms. The black drum fish, for example, possesses one of the highest bite forces among modern animals and uses powerful, molar-like pharyngeal teeth located in its throat to grind up hard-shelled mollusks.
The black drum’s teeth are highly adapted for resisting wear. Similarly, rays and pufferfish have evolved flattened, plate-like teeth fused into crushing dental batteries designed to pulverize the shells of clams, mussels, and crabs. The cownose ray, for instance, uses these powerful plates to efficiently process its bivalve diet.
Larger crustaceans also participate in this crushing strategy, often preying on their smaller relatives or thin-shelled mollusks. Crabs like the blue crab and green crab use their strong claws, known as chelipeds, to open shellfish. They employ different techniques, such as crushing the entire shell, chipping away at the valve edges, or forcing the two halves of a bivalve apart. These specialized claws allow them to efficiently manipulate and dismantle the protective shell.
Bore and Pry Specialists: Invertebrate Hunters
Invertebrate predators, lacking the crushing force of fish jaws or crab claws, employ distinct chemical and subtle mechanical methods to breach a shell’s defense. Sea stars are famous for their unique prying technique, targeting bivalves like clams and mussels. The sea star uses hundreds of tiny tube feet to secure itself to the two halves of the shell and applies a steady, relentless pull.
This sustained pressure eventually causes the bivalve’s adductor muscles to fatigue. Once a minuscule gap is created, the sea star engages in stomach eversion. The predator pushes its stomach out through its mouth and inserts it into the narrow opening of the shell. Digestive enzymes are then secreted directly onto the soft tissue of the prey, dissolving it externally before the resulting liquid is absorbed and the stomach is retracted.
Other invertebrate specialists, such as predatory marine snails like whelks and moon snails, are known for their precision drilling. When a moon snail finds a buried bivalve, it uses a ribbon-like organ called a radula to bore a near-perfect, circular hole through the shell. This mechanical drilling is aided by acidic secretions that chemically soften the shell material, making the job faster. Once the hole is complete, the snail inserts its proboscis and releases digestive enzymes to liquefy the prey, which it then consumes through the drilled opening.
Marine Mammals and Birds: Force and Finesse
Marine mammals and birds often rely less on specialized internal anatomy and more on learned behaviors or strategic use of their environment to access shellfish. The sea otter is a prime example of an animal that utilizes tools to overcome the shell barrier. Floating on its back, the otter places a rock on its chest and uses it as an anvil, repeatedly striking the shell of a clam or mussel against the hard surface until it breaks.
Walruses, on the other hand, employ a powerful suction feeding mechanism for consuming clams buried in the seafloor. After locating prey with their sensitive whiskers and clearing sediment with jets of water, they seal their powerful lips around the clam. The walrus then quickly pulls its piston-like tongue back into its mouth, creating a powerful vacuum that sucks the soft clam body right out of its shell.
Shorebirds like the American oystercatcher use their strong, wedge-shaped bills with surgical precision. They often search for bivalves that are slightly ajar and, in a swift motion, stab their bill into the gap to sever the adductor muscle that holds the shells closed. Other birds, such as gulls, have been observed carrying hard-shelled prey high into the air and dropping them onto rocks or pavement, relying on gravity and impact to crack the shell open and access the meat inside.