The nurse shark, Ginglymostoma cirratum, is a common, slow-moving species often found resting on the seafloor in warm, shallow coastal waters. Characterized by its docile nature, this shark is a specialized benthic predator. It utilizes unique behaviors and physical traits centered on a specific suction feeding strategy.
Primary Components of the Nurse Shark Diet
The diet of the nurse shark is heavily dominated by benthic organisms. These sharks are specialist feeders, primarily targeting prey that is stationary, slow-moving, or hidden within the substrate. Their preference is for hard-shelled invertebrates, which they are uniquely equipped to process.
Crustaceans form a significant portion of their meals, including crabs, shrimp, and spiny lobsters. They also consume various mollusks, such as clams, oysters, and squid, which they extract from their protective shells. Sea urchins and other echinoderms are also regular prey items, demonstrating the shark’s ability to handle spiny or armored food sources.
While invertebrates are the main focus, nurse sharks also prey on small fish and rays that rest on the bottom at night. They rarely pursue fast-moving, mid-water (pelagic) fish, instead taking advantage of those that are sleeping or sheltering in crevices. Stomach contents occasionally include algae or coral fragments, which are likely ingested accidentally due to the method they use to capture their primary prey.
Unique Hunting and Suction Feeding Techniques
The nurse shark’s foraging strategy is distinct from the bite-and-tear methods of larger shark species, relying on a slow, methodical approach and a powerful vacuum mechanism. They are primarily nocturnal feeders, becoming most active after sunset when many of their prey items are resting or emerge from cover.
The primary mechanism for capturing food is an extreme form of suction feeding. The shark approaches its prey and rapidly expands its pharynx and buccopharyngeal cavity, which generates a powerful, negative pressure vacuum. This force effectively “hoovers” the prey directly into the mouth, often pulling it out of sand, coral crevices, or rock holes where it may be hiding.
The power of this suction is substantial and has been observed to be strong enough to dismember smaller prey or extract conchs from their shells. Since the effective suction distance is limited to about three centimeters in front of the mouth, the shark must stalk and position itself directly over the target. This constraint often leads the nurse shark to forage close to the substrate, sometimes even using its pectoral fins to maneuver itself into a favorable position.
Physical Adaptations for Bottom Feeding
The nurse shark possesses a suite of anatomical features perfectly suited for its bottom-feeding, suction-based diet. Its mouth is small, subterminal, and positioned on the underside of its broad head, which enables it to feed directly on the ocean floor. The small, laterally enclosed gape is designed for creating the necessary vacuum seal rather than taking large, aggressive bites.
Two prominent sensory organs, called barbels, hang near the nostrils and play a crucial role in locating hidden prey. These fleshy, whisker-like appendages are brushed along the sand or substrate to detect chemical cues from invertebrates buried out of sight. This chemical detection is supplemented by electroreception, which allows the shark to sense the faint electrical fields generated by living organisms.
The jaws of the nurse shark are robust, and its mouth contains multiple rows of small, pointed teeth. These teeth are specialized for crushing and holding, rather than tearing, making them ideal for breaking the hard exoskeletons of crabs and the shells of mollusks. The muscular pharynx and specialized jaw structure allow for the rapid expansion required to generate the highest subambient pressures reported for an aquatic-feeding vertebrate.