Dr. Rita Mehta, a UCSC biologist studying animal physiology, behavior, and evolutional morphology, has provided some of the most significant research findings on moray eels. After discovering a unique feature of their physiology, Dr. Mehta now considers how this feature contributes to their eating habits and role within their ecosystems.
The moray eel in a nutshell
Moray eels encompass over 200 species of eels, with a wide variety of sizes and colors. Morays are known for their serpentine like body and large head, with a long snout and big piercing eyes. Their coloring ranges from black to orange to green with a spectrum of speckled, spotted, or striped patterns. Some species also have camouflaging abilities.
While morays can live in marine or brackish waters, they prefer warm-watered coral reefs. Their diet consists of fish, mollusks (like octopus), and hard-shelled invertebrates (like crabs). Like fishhooks, their small sharp front teeth are pointed backward to keep their prey from escaping while hunting.
Most fish have what are called pharyngeal jaws, a set of jaws located in the throat, which, in addition to the normal set of jaws in the mouth, helps them wrangle their prey. Using a suction-like method, fish suck prey into the oral cavity of the mouth; water sucked in with the prey carries it to the pharyngeal jaws in the throat, which then grab and pin down prey for digestion.
While similarly equipped with a second set of jaws in the throat, moray eels are a little different. They have what are called raptorial pharyngeal jaws, which play a more active role in pinning down prey. Moral eels catch their prey with the sharp recurved teeth of their first set of jaws, before launching their pharyngeal jaws from the throat into the oral cavity to hook the prey and reel it backwards. This feeding method relies on elongated muscles, which expand and contract with the launching method to control the jaw set.
According to Dr. Mehta, “This is the first described case of a vertebrate using a second set of jaws to both restrain and transport prey.” Hitherto, the existence of these jaw types were only found in a select few species of invertebrates, illuminating a novel feeding regime for species worldwide.
Eels, with their elongate bodies, (a shape they share with snakes, meaning their internal muscles and bones are lengthened) survive in the twisted spaces of coral reefs. Their shape allows them to hide from predators in the coral, but also allows them to explore tight crevices for food. In doing so, they can corner prey, stick their head in, and snatch the prey out by launching their pharyngeal jaws forward.
When it comes to larger prey, morays also use what is called a ratcheting technique, which Dr. Mehta describes as walking their jaws over prey to creep it into their throat. For this process, the first set of jaws unlock, separating into two halves that can move freely from one another. As the prey is guided through the eel’s mouth, the pharyngeal jaws then take over, dragging the prey the rest of way into the throat. Despite the use of the raptorial pharyngeal jaws, the ratcheting technique is not unique to the moral eel - their terrestrial counterparts, snakes, are known for this technique as well.
The combination of these two feeding systems in the moray eel - the raptorial pharyngeal jaw and the ratcheting technique - not only illuminates a new feeding dynamic for aquatic vertebrates, it also promotes new questions concerning the morphology and adaptability of this jaw system.
Where to go from here
As they are the only known aquatic vertebrates to use the second jaw set in the launching/retracting manner, there are many unknowns. Moray eels are keystone species, which means the play a crucial role in maintaining their ecosystem’s equilibrium. When these ecosystems are thrown out of balance, insight into how the moray eels feed could be crucial in restabilizing the ecosystem and protecting other species up and down the food chain.
Thus, questions like - what other species have this feeding system? How can we find them? What other fish can provide similarly enlightening findings? What other differences are there between moray eels and other species? – have arisen while studying these creatures. Dr. Rita Mehta and her team at Mehta Labs, through the UCSC Longmore Marine Center, hope to answer these questions and more.
Distribution and habitat associations of the California moray (Gymnothorax mordax) within Two Harbors, Santa Catalina Island, California
Elongation of the Body in Eels
Morphological and Functional Innovation: Raptorial jaws help moray eels swallow large prey