The common perception of sharks involves large, open-ocean predators. However, the diverse world of sharks includes hundreds of species with specialized feeding habits. Many species have developed a diet centered on hard-shelled organisms, a strategy known as durophagy. This specialized niche confirms that many sharks consume crabs and other invertebrates as a regular food source. These crustacean-loving sharks typically inhabit the ocean floor, where they locate and process their heavily armored prey.
Sharks That Prey on Crabs
The Bonnethead shark, a smaller member of the hammerhead family, is one of the most dedicated crab consumers. Studies show that crabs, particularly the blue crab (Callinectes sapidus), often constitute between 85% and 97% of their total diet by volume in some regions. This dietary preference makes them specialists in estuarine and coastal waters where crustacean populations are abundant.
Nurse sharks are slow-moving, bottom-dwelling species that rely heavily on crabs and other benthic invertebrates. They are nocturnal hunters, foraging along the seafloor and coral reefs. Their diet consists largely of crustaceans, including various species of crabs, shrimp, and spiny lobsters.
Smoothhound sharks, a group of slender, bottom-dwelling sharks, are well-documented crustacean feeders. Found in both the Atlantic and Mediterranean, they frequently consume crabs and lobsters. This reflects an opportunistic feeding strategy tied to the availability of armored prey on the substrate.
Adaptations for Hard-Shelled Prey
Sharks that consume armored prey possess distinct anatomical features enabling them to crush tough exoskeletons. Unlike the serrated teeth of sharks that target soft-bodied fish, the teeth of durophagous sharks are designed for grinding. Bonnethead and Nurse sharks feature rows of flat, plate-like teeth, referred to as molariform teeth, which function like a crushing pavement.
These crushing teeth are supported by powerful jaw musculature that generates the force necessary to break through the hard outer shell of a crab. The jaw structure is more robust and less flexible compared to sharks that rely on slicing for prey capture. For the Bonnethead shark, crushing prey involves a distinct mechanical action, utilizing a powerful second jaw-closing phase to process the crab before swallowing.
A secondary adaptation is the use of suction feeding to capture and ingest prey hidden in the substrate. Nurse sharks, for instance, rapidly expand their mouths to create a vacuum, effectively “slurping” crabs and other invertebrates out of sand or crevices. This combination of specialized dentition and strong suction allows these sharks to exploit a food source inaccessible to many other marine predators.
Broader Crustacean and Mollusk Diets
While crabs are a primary food source for many specialized sharks, their diet extends to a wider array of hard-shelled invertebrates. This broader feeding habit is characteristic of their benthic lifestyle, where they target organisms dwelling on or within the seafloor. For the Nurse shark, this includes shelled mollusks like conchs and sea snails, which are extracted using the sharkâs crushing force or suction.
Smoothhound sharks, often found on soft, muddy bottoms, consume cephalopods and bivalves in addition to crustaceans. This adaptability ensures they maintain a consistent food supply as prey availability changes. The dietary scope demonstrates that for these species, consuming hard-shelled prey is a comprehensive feeding strategy. The consumption of these armored animals places durophagous sharks in an important ecological role, helping to regulate the populations of bottom-dwelling invertebrates.