Coral reefs are the “rainforests” of the sea. They support a tremendous diversity of species, including top predators like sharks, rays, eels, and sea turtles. Predators play an important role in reef communities by controlling the population and behavior of prey animals (especially herbivores) living farther down on the food chain.
What They Eat
Predators at the top of the reef food chain feed on other animals living in the reef community—often for short periods at night. Many stalk, ambush, or use speed to pursue their prey—and have sharp pointed or blade-like teeth, adapted for seizing and holding prey and for piercing and tearing flesh.
Where They Live
Coral reefs grow in shallow, warm water, usually near land. Small predators inhabit holes and crevices in the reef’s structure. Larger predators live in the open ocean, on the ocean’s floor, or near shore, and only patrol the reef to feed. In the Atlantic Ocean, coral reefs can be found off the coast of Florida to the Caribbean, and down to Brazil.
What They Do
The coral reef is an intricately balanced system where all plants and animals fill a special niche and serve a specific function. Top predators keep reef communities healthy by preventing population explosions of species farther down the food chain. Many also act as scavengers and eat weak organisms.
How They’re Doing
Reefs and their complex communities are under threat due to a variety of natural and human disturbances including coastal development, destructive fishing practices, pollution, climate change, and invasive species. All seven species of sea turtles are currently endangered, as are dozens of species of sharks and other large predatory fishes. The U.S. Fish and Wildlife Service also lists two species of corals, Elkhorn and Staghorn, as endangered.
Shark Reef displays many of the predatory fish and sharks found patrolling coral reefs. Because these fish and sharks would prey on many of the smaller coral reef fish species, they are displayed in a separate exhibit. Southern stingrays, a green moray eel, and two sea turtles also share this exciting exhibit.
Sandtiger sharks are found in the shallow, coastal tropical waters of all oceans except the central and eastern Pacific. They dwell on the bottom and near the surface, and have been found at depths of nearly 4,000 ft. Adult sharks are 4-8 feet long, have hunch backs, narrow snouts, and a golden-brown sheen. Some have large reddish or brownish spots scattered on their bodies. With their toothy grin and large eyes, these sharks have a ferocious appearance.
This nocturnal hunter feeds on bony fish, small sharks and rays, octopus, and large crustaceans. Awl-shaped, dagger-like teeth are excellent for grasping and eating prey whole. Sandtiger sharks often feed cooperatively, which makes them socially unique among sharks.
Sandtiger sharks are often found in groups of a few dozen, hovering in caves or near reefs or shipwrecks. This shark has an interesting method of buoyancy control — it swallows air at the surface and holds it in its stomach to maintain neutral buoyancy while hunting for prey. Sandtigers migrate, coming toward shore during the summer and moving southward or to deeper waters in the winter.
Female sandtiger sharks are ovoviviparous (producing living young from eggs that hatch within the body). This species is unique because of the intra-uterine cannibalism that occurs–only one embryo survives. Young are 3 feet long at birth and have sharp, functional teeth.
Sandtiger sharks are considered a vulnerable species. In the 1960s these sharks were almost wiped out due to spearfishing, over-collecting, being fished for their livers, which are rich in vitamin A, and for shark fin soup. They are still trophy hunted for their jaws, liver, and valuable flesh. Scientists believe declining shark numbers is leading to an increase in the number of groupers, resulting in a decline of parrot fish and thus leading to more algae overgrowing and killing coral reefs.
Southern stingrays inhabit temperate waters of bays and estuaries from New Jersey to Brazil, as well as the Gulf of Mexico. Like most rays, they have a flat, disc-shaped body, wing-like pectoral fins, no distinct head, eyes on top of their head, and a mouth underneath. Southern stingrays are uniformly brown in color, with lighter shading underneath.
Rays feed on a wide variety of bottom organisms, such as crustaceans (shrimp and crab), mollusks (snails and shellfish), and worms. They crush their food with strong plates in their mouths and expel sand through their spiracles (just behind their eyes). Some rays will “mine” the sediment using a stream of water to dislodge prey.
Stingrays are ocean floor prowlers. When sensing prey underneath, they drop to the ocean floor—trapping it with their bodies. These graceful gliders like to hide underneath the sand with only their eyes, spiracle, and tail poking out, and will use their large pectoral fins to loosen and scoop food out of the sand.
Breeding season for stingrays is from late spring to early summer. After a gestation period of 5 months, females give birth to 3-5 pups. Development is ovoviviparous (pups hatch from their egg capsules while inside the mother’s uterus and are born soon after).
Sea turtles are air-breathing reptiles found in the tropical and temperate waters of the world’s oceans. They can be found in different areas of the ocean at different times of the year. In the fall and winter, they disperse to their favorite feeding grounds-often near reefs. In the early spring and summer, females may leave the water and return to their home beach to nest. There are seven species of sea turtles, ranging in weight from 100 to 1,000 pounds, with lifespans as long as 100 years.
Sea turtles’ diets vary depending on the species. Kemp’s Ridley sea turtles are carnivores, feeding on crabs, mollusks, jellyfish, mussels, and fish. Green sea turtles are carnivorous until age one, and then become herbivores, feeding primarily on sea grasses.
Streamlined bodies and flippers make these large animals powerful swimmers and divers-some species routinely diving to depths greater than 1,000 feet and staying underwater for several hours. Unlike their freshwater relatives, sea turtles have a special gland that rids their bodies of excess salts. The gland empties in the turtles eyes, which makes it look like it is “crying” when it comes ashore. These tears help keep the eyes free of sand while the females dig nests. Because they are unable to pull their heads and limbs into their shells for protection, sea turtles rely on camouflage, speed, and protective shelter to avoid predators.
Many sea turtles nest along the southeast coast of the United States. Small numbers of green sea turtles nest on the Atlantic coast of Florida. Most species are solitary nesters. Females come to shore every 3-5 years to nest 3-6 times in a season. After digging a nest with her flippers, she will lay about 100 ping pong ball-sized eggs. After 60 days, hatchlings will emerge from the nest and make a mad dash to the ocean. Precious few will reach maturity (20-30 years). Kemp’s ridley turtles gather in large numbers to nest. These events are called an “arribada” and take place on a small strip of beach at Rancho Nuevo, Mexico.
Most species of sea turtles are considered either critically endangered or endangered. Their populations have declined due to commercial harvest of turtle meat, eggs, skins for leather, and shells for ornaments and jewelry. They die from ingesting marine debris, such as plastic bags, or get caught in nets as bycatch and drown. Currently, several programs and preserves have been established worldwide to help protect sea turtles and their habitats. Due to their endangered status, only injured seas turtles may be exhibited at zoos.
Green Moray Eels
Moray eels are found in tropical reefs and shallows from New Jersey to Brazil, including Bermuda and the Gulf of Mexico. Nocturnal and shy by nature, green morays often hide in crevices and holes in corals. Their long, snake-like bodies have no scales, just leathery skin, and their dorsal, caudal, and tail fins are joined together to create one long fin down their back and up their belly. They often anchor their tails between rocks while they hide during the day. Moray eels can reach up to 8 feet in length.
Moray eels have large mouths and sharp teeth. They feed on fish and crustaceans, especially crabs, and use their long, slender bodies to enter holes and crevices in search of hidden prey.
Habits and Adaptations
Eels are secretive and employ stealth as a primary hunting technique. Despite warning predators with a large open mouth and sharp teeth, morays are not aggressive and do not usually bite unless provoked. They are not poisonous, however the bacteria in their mouths can cause serious infections. Moray eels begin adult life as males, then later change to females (sex reversal). Because of their secretive nature, little is known about their spawning habits.
Cobia can be found on the western coast of the Atlantic from Massachusetts to Argentina, often in open waters. They prefer water temperatures between 68°-86°F and often seek shelter in harbors and around wrecks and reefs. Cobias have broad, flat heads and long, streamlined bodies. They are not very strong swimmers. They are dark brown to silver, paler on the sides, with two narrow dark bands extending from the snout to base of tail fin.
Cobia are opportunistic carnivores, feeding primarily on crabs, squid, and other fish. They are voracious eaters, and often engulf their prey whole. They frequently follow large animals like sea turtles, sharks, and rays to scavenge leftovers.
Related to remoras, cobia often swim near sharks’ tails.
Jacks & Pompanos
Jacks and Pompanos are similar in behavior and physiology.
Jacks are primarily found hunting near coral reefs. They live in the tropical and temperate waters of the Atlantic Ocean, along the eastern coast of the U.S. and south to Brazil and Uruguay. These fast-swimming fish have large eyes, excellent eyesight, and are one of the largest predators on the reef. Jacks are typically light in color, usually silver with red pigmentation which disappears in dark ocean water. They prefer mid to deep water, but may be found near the surface at dusk and dawn.
These strong-swimming carnivores rely on speed and strength to catch their prey, which includes small fish, copepods, and other ocean animals.
Jacks are often found swimming with sharks, but when roaming the open sea they school as a defense mechanism. Their young are particularly vulnerable to predation, and have developed an interesting strategy to avoid getting eaten. To avoid detection and prevent other predators from approaching, they swim very close to predators in the blind spot right between their eyes. Jacks can also be seen hitching a free ride in the bow wake of their predatory “companions.” Juveniles hide among jellyfish, debris, plants, etc, and have a deeper and sleeker appearance then the adults.
Atlantic Goliath Grouper
Atlantic goliath groupers are found in tropical and subtropical waters of the Atlantic Ocean from North Carolina to Brazil, and throughout the Caribbean and Gulf of Mexico. They are also found along the east coast of Africa from Senegal to Congo. They prefer the sheltered habitats of coral reefs, and especially shady areas such as shipwrecks, rock ledges, and caves. Atlantic goliath grouper have a broad, flat head and mouth, and can grow up to 8 feet long and weigh over 700 pounds.
These hunters are not built for speed over long distances and prefer to ambush prey, rather than pursue it in open water. The diet of these large predators consists mainly of crab, lobster, fish, octopus, and young sea turtles. Most prey is simply engulfed with a snap of the jaws and swallowed whole.
Habits and Adaptations
Atlantic goliath groupers are often spotted or dark in color, allowing them to camouflage with their surroundings. Small groupers may be preyed upon by barracuda, king mackerel, moray eels, and sharks. Full grown goliath groupers are only preyed upon by humans and large sharks. When threatened, an Atlantic goliath grouper will defend its territory with aggressive body language and a distinctly audible rumbling sound. The sound is produced by contracting the swim bladder and can travel great distances underwater. It’s thought that the sound can also be used to communicate with other goliath groupers.
These puffer fish primarily inhabit coral reefs and other warm shallow waters. They can occasionally be found in temperate waters, when swept there by ocean currents. As their name suggests, puffers’ bodies are covered with obvious spines. Usually brown in color, with some yellow on the underside, these stocky, slow swimming fishes have a large head and a “box-shaped” body.
Porcupine fish use their strong beaks to crush coral polyps, mollusks, crustaceans, crabs, and sea urchins. They also feed on small fish, and have developed the ability to feed on animals with stinging cells without suffering any of the harmful affects.
Puffers hide in coral and as their name implies, can puff up two to three times their normal size by sucking air or water into a special chamber in their abdomen. This balloon effect causes them to become more than a mouthful to would-be predators. Puffers employ a number of defenses to avoid getting eaten: they are covered with sharp spines, their internal organs contain an extremely toxic nerve poison, and when cornered they can bury themselves in the sand. They also have tough skin and lack scales.
This important food fish can be found in warm coastal waters, from Massachusetts to Brazil, including Bermuda and the Gulf of Mexico. They have a triangular-shaped head and a notched tail, and are capable of inflicting injuries to unsuspecting fishermen with their well developed teeth. Snappers are named for the characteristic snapping noise they make when they are taken off a line or hook.
Snappers use speed and stealth to catch their prey—usually crustaceans or other fish.
Many snappers have a broken color pattern and are colorful in their natural setting (colors fade in captivity). They use a form of counter-shading as camouflage. Predators approaching from the bottom see a white belly that blends with the bright ocean surface above. Predators approaching from above, such as seabirds, see a dark back that blends in with the ocean depths. Snappers have large eyes that help them see better while hunting at night.
Tarpon are found in shallow tropical and temperate waters along the eastern and western Atlantic coasts. They are also found along the Pacific coast of Panama. Prized as sport fish, they may grow beyond 6.5 feet in length and weight up to 350 pounds.
Juvenile tarpon feed on zooplankton, crustaceans, and insects. Adult tarpon diet includes fish and larger crustaceans, such as crabs and shrimp.
Tarpon are tolerant of a wide range of salinity and oxygen concentrations. When swimming in oxygen-poor water, tarpon can gulp air from the surface. A large female tarpon may lay 12 million eggs, which drift in ocean currents to near-shore areas. Hatchlings are larval, almost transparent, and look more like a clear strip of ribbon than a fish. The eggs and larval young become an intricate part of the plankton that serves as the base of numerous ocean food chains. When they reach about 1.5 inches in length, they metamorphose into tiny versions of their parents complete with prominent silver scales.
Triggerfish usually spend a large portion of their lives near a coral reef-inhabiting areas in coastal waters from New York to Brazil. Small eyes set high on a large, angular head and jaw give them a “bucktoothed” appearance. Their bodies are covered with bony plates instead of scales, and lacks a protective mucous layer. This aggressive species is known for defending their nests and even other triggerfish.
Triggerfish have powerful jaws and teeth that allow them to easily crush hard-shelled prey like crustaceans, mollusks, coral, and sea urchins. They also eat algae and small fish. The Queen triggerfish will blow mouthfuls of water at sea urchins to flip them over and expose their softer underparts.
Triggerfish can watch for predators from all sides by rolling their eyes independently. To defend themselves, they wedge themselves into small holes by erecting their first dorsal spine and pelvic girdle. A second “trigger” spine locks the first spine into an upright position, making it nearly impossible for predators to pull them out of the hole. This species uses color and pattern to confuse their predators. The Queen triggerfish is quite colorful, with a striped face and long tips to the tail fin. Gray triggerfish often have blue spots on the upper portion of the body, and white spots or lines on the lower body half
- The “wingspan” (disc-size) of a southern stingray can reach up to 5 feet.
- Green sea turtles can stay under water for as long as five hours. Their heart rate slows down to conserve oxygen.
- Green moray eels are really blue. Their bodies are coated with a yellow-colored slime that makes them look green. The slime helps protect their skin from the jagged surface of the caves and crevices where they hide.
- Sharks and rays don’t have bones. Their skull, spine, and fin supports are made of cartilage, the same lightweight, flexible material found in the bendable parts of a human’s nose and ears.
Coral reefs are among the most important ecosystems on Earth. They provide shelter to thousands of species of marine fish and invertebrates while also protecting coastlines from erosion and storm damage. Commercial and recreational fishing industries rely on healthy reefs to support strong fish populations. The tourism industry surrounding coral reefs plays a major role in the economy of many countries.
Unfortunately, reefs are dying at an alarming rate. Physical destruction, rising water temperatures, depleted fish populations and coastal pollution have wrecked havoc on this fragile ecosystem. A lot of work is required to stop the loss of reefs and return corals to a healthy population. The Minnesota Zoo has made coral reef restoration a priority in its mission to save wildlife.
Things the Zoo's Done/Doing
In 2017, Christoph Noetzli, aquarist at the Minnesota Zoo, joined SECORE International and traveled to the Caribbean island of Curacao to assist with the ongoing efforts to restore their reefs. SECORE is a global organization that joins coral biologists and public aquarium professionals to research and implement the most efficient strategies in coral reproduction and reef restoration.
While in Curacao, Christoph and fourteen other aquarists from around the world collected coral spawn during multiple night dives. In a ten day period, tens of thousands of coral embryos were created through fertilization in the lab. These embryos then settled on to ceramic tiles and were planted back out on to the reef. This process of spawn capture, fertilization, and outplanting allows for the reef to regrow with healthy and genetically diverse corals.
In 2018, the Minnesota Zoo became became an official sponsor of SECORE International and is proud to support their efforts in restoring coral reefs. SECORE conducts fieldwork in Curacao, St. Croix, Bahamas, Mexico, Philippines, and Guam.
Christoph’s participation in the Curacao workshop was made possible by the Minnesota Zoo’s Ulysses S. Seal Conservation Grant Program.