Coral reefs provide homes to nearly 25% of all marine fish species (an estimated 4,000 coral reef fish species worldwide).
- Fun Facts
- Behind the Scenes
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Where at the Zoo
Elkhorn & Staghorn coral
10 coral species endemic to Galapagos Islands
Where in the World
Central America & Caribbean
Coral reefs are among the world’s most diverse ecosystems, second only to tropical rainforests. Large numbers of different types of fish are able to live and thrive close together here, because each has adapted its own unique way to feed, live, and reproduce in this complex, interconnected environment.
What They Eat
The diets of reef fishes are highly specialized. Each species has developed special physical adaptations or unique feeding strategies in order to compete successfully for food. Depending on the species, they may feed on algae, living coral, plankton, other fishes-even the parasites of larger fishes.
Where They Live
Corals thrive in warm, clear, shallow water (usually near land). Most reef-building corals need temperatures between 70º F and 85º F to survive, so many reef fishes are found in warm, tropical waters near the equator. Habitats of fish species living in a reef community can be divided by territory, diet, and time of day.
What They Do
Coral reefs provide food, nursery areas, and safe havens from predators to an amazing variety of animal and plant species. During the day, the reef is dominated by the colorful, plant-eating fishes (herbivores). At night, these fishes hide among the corals to escape falling prey to the reef’s abundance of carnivores.
How They’re Doing
Coral reef fishes depend on healthy corals to survive. With 25% of coral reefs already destroyed, some scientists estimate that the remaining reefs may disappear completely by the year 2030. Temperature changes, run-off pollution, sedimentation, and harmful fishing and recreation practices destroy reefs.
Where at the Zoo
Elkhorn & Staghorn coral
10 coral species endemic to Galapagos Islands
Where in the World
Central America & Caribbean
Remoras hitch piggyback rides on sharks and hang on with suctions cup discs on their heads. Remoras keep the shark’s skin free of parasites and in return get to eat bits of leftover food.
A coral colony is like an enormous limestone condominium, getting its bright color from algae tenants. Algae make sugary food for coral from seawater and sun and recycle waste products into oxygen and food.
Coral reefs are like underwater rainforests:
- Both are wondrous, complex ecosystems.
- They shelter the most diverse collection of plants and animals on earth.
- Combined, they house the greatest density of species on the planet.
- Reefs and tropical rain forests both occur in warm climates.
- Creatures that reside in them depend on each other to live.
- People living nearby need them to survive.
- They are being destroyed at phenomenal rates.
- People are their worst enemy.
Corals and sponges are animals. Most earn their names from something they resemble on land.
- Elkhorn coral looks like horns or antlers.
- Brain coral is dome-shaped with irregular surface patterns.
- Table coral looks like you could set it for dinner.
- Tube sponges resemble smoke stacks.
- Chalice sponges are shaped like a short-stemmed wine glass.
At the Minnesota Zoo, our spectacular floor to ceiling underwater viewing windows on the Tropics Trail allow you to get a close-up look at a variety of fish species without ever getting wet! Watch our aquarium staff scuba dive with the sharks and tropical fish for a feeding. The divers are equipped with special two-way microphones to talk about the exhibit and answer your questions. Coral Reef fishes are fed daily at 10:30 .m., and Coral Reef sharks are fed daily at 3:00 p.m.
The Minnesota Zoo’s Coral Reef exhibit contains 82,500 gallons of water. Based on a 70 gallon bathtub, it holds enough water to fill about 1,178 bathtubs! The tank is 24 ft. x 60 ft. and averages 12 ft. in depth. The window space is 55 ft. long and made from 6-inch thick acrylic (plastic). The water temperature is a balmy 75º F.
Although the “corals” and “sponges” in this reef are artificial (cast or carved), you can also see “farm raised” corals (live corals cultivated artificially), in Discovery Bay.
Coral reefs are fragile, living ecosystems that are increasingly under pressure due to pollution, disease, and habitat destruction. Not only do they provide habitat for many endangered marine species, but several coral species themselves are now currently listed as threatened or endangered.
Natural threats to coral reefs include hurricanes, typhoons, El Niño, and invasive species. Human threats to corals include destructive fishing practices, coastal development, pollution, and rising global temperatures.
Things the Zoo's Done/Doing
Eco-Corps is a grassroots level conservation effort based on the island of Viti Levu in Fiji. The group’s mission is to conserve Fiji’s natural and cultural resources through research, education, and sustainable development programs in local communities. Their four major conservation areas include: marine and terrestrial biodiversity surveys, the development of an underwater park, community education, and wastewater management.
In January 2007, Melanie Sorenson, Education Interpretive Naturalist at the Minnesota Zoo, spent four weeks in Fiji working with Eco-Corps. While there she assisted in the development of a snorkeling trail and a reef walk tour. She also worked with local villagers helping record flora and fauna and developed a training book for local guides and tourists and interpretive graphics, pamphlets, and field sheets for these projects.
The Minnesota Zoo’s Ulysses S. Seal Conservation Grant Program provided Melanie with financial support to cover some of her travel and lodging costs and to purchase supplies for this program.
Learn more about this conservation project:
Minnesota Zoo’s Coral Reef exhibit was designed and constructed with reef conservation in mind. To protect living reef communities, the exhibit was made from artificial corals, either carved or cast from lifelike molds. Reef fishes were collected carefully by hand, and the reef community was not harmed in any way by our methods.
Coral reefs support an amazing diversity of life. Corals that build reefs are actually primitive animals that use energy produced by algae for food. Since algae need strong sunlight, reefs are only found in clear, shallow waters near the equator. The rock-like reef structure is the calcium carbonate skeletons of many generations of corals.
An individual coral animal is called a polyp. Like its relatives the jellyfish and anemones, these tiny animals are armed with stinging tentacles that capture food as it floats by. Reef-building polyps (hard corals), make external limestone skeletons from minerals in the seas. Microscopic algae living inside polyps use coral waste and sunlight to photosynthesize food.
Some corals live alone, and others live and grow in groups called colonies. A reef begins when a drifting polyp finds a resting place in warm, shallow water and begins to “bud”, or produce new polyps. Tiny skeletons fuse, eventually creating the common skeleton of the reef. As old polyps die, each succeeding generation builds its home upon the foundation of skeletons left by the past. Over time, multiplying polyps build colonies in many shapes. They can look like mushrooms, tables, antlers, or even brains. Factors that affect the way in which a colony grows include the depth of water, amount of sunlight, water movement, and temperature.
Despite their plant-like appearance, sponges are primitive animals with bodies like water canal systems. They feed by drawing seawater through the tiny holes in their surface. Particles from the water are trapped inside the bodies and absorbed directly into the their cells.
Like corals, sponges come in a variety of shapes. Upright, branched forms tend to live in calmer waters. Large, cone-shaped forms often grow in the sandy patches of lagoons. Sponges play host to numerous small animals, which live inside their bodies and siphon off food particles as water is drawn into the sponge.
Coral Reef Fishes
Life teems in the coral reef, sustained by the food found there and protected by the reef’s stony structure. Of the many species of marine animals that call the reef home, perhaps none is more colorful and diverse than the fishes. Scientists don’t know exactly how many species of coral reef fishes exist, but there are probably at least as many species as there are different ways to feed, reproduce, and hide among the cracks and crevices in the reef. Several of the most interesting species, including those mentioned below, can be seen in our Coral Reef Exhibit at the Minnesota Zoo.
Feeding Strategies and Diet
To compete successfully for food, coral reef fishes need to be highly specialized. Each species has evolved physical adaptations, or unique feeding strategies.
Reef fishes may pick, scrape, grind, crush, grasp, and tear to get their food. Their mouth, teeth, and jaws are shaped to match their feeding style. Parrotfish have beak-like mouth parts for scraping and biting algae from coral surfaces. Wrasses use their protruding teeth to nibble at coral, worms, and crustaceans. With large canine teeth in both jaws, snappers feed mostly on crustaceans like shrimp and crabs.
Some fish species mimic the color and swimming patterns of non-predator species to trick unsuspecting prey. Hawfish hunt for prey by ambush. Because they have the ability to blend in with their surroundings by changing their body color or patterns, they may go unnoticed by prey until it’s too late.
Mutualism is a symbiotic relationship between different species in which both individuals benefit from the association. These relationships are extremely common in coral reef communities. One of the best known is between the clownfish (a kind of damsel fish) and the sea anemone. They work together to share food and avoid predators. As juveniles, clownfish incorporate the anemone’s mucus into their own by “rubbing” its tentacles. This fools the anemone into thinking the clownfish is part of itself so it no longer stings it. As adults, the clownfish fight off intruders, such as anemone-eating butterflyfish, and use the anemone’s tentacles to avoid predators. To feed, they share each other’s catch.
Some fish are like carwash attendants. They provide a service by removing parasites from other fish. At reef cleaning stations, large fish line up and signal the cigar-shaped cleaner wrasse that they are ready to be cleaned. Cleaners then hurry all over the fish’s body, eating parasites and food remains. Remoras hitch piggyback rides on sharks and hang on with suction cup discs on their heads. Remoras keep the shark’s skin free of parasites and in return get to eat bits of leftover food.
Time of Day
Large predators like whitetip reef sharks use olfactory and sonar to locate food at night. Whitetips feed on fish, octopus, and crustaceans. They will follow a fish into a hold or crevice and attempt to grab it, or block the hold with their body until the fish tries to leave. Zebra sharks are also thought to be nocturnal. They are bottom feeders, eating mollusks, shrimp, crab, and small fish.
Reef fishes, with the exception of sharks, may lay millions of eggs each spawning season. Due to high mortality rates, most juveniles never reach maturity.
Spawning and eggs
Many species of reef fish, like hawkfish, spawn in pairs or groups all year long-usually at night. Other species, like the Milkfish, mate in conjunction with lunar cycles, spawning only during new or full moons. Butterflyfish release eggs and sperm into the water, and the larvae drift and swim freely for more than a month before finding their way to a home reef. Clownfish spawn and lay eggs near anemones. Their eggs remain attached to the reef and guarded by the males, until hatching after 4-5 days. Zebra sharks lay two or more eggs in brownish-black cases attached to the bottom. Hatchlings are 8-13 inches long and have zebra-like markings.
Whitetip sharks are viviparous (give live birth). Gestation lasts around five months with 1-5 pups being born.
Many coral reef fish species, such as wrasses, parrotfish, and angelfish may start out as one sex (usually female) and change to the other over time. A population consisting largely of breeding females may help increase a species’ numbers and give it a genetic advantage.
Reef communities contain far more carnivores than herbivores. As result, danger lurks around every corner, and to survive, prey fish have adapted some unique ways to protect themselves.
Color and camouflage
Color and pattern help a fish hide, defend a territory, or warn predators that it’s toxic to eat. Schooling fish are often silver in color. By breaking up light patterns, the silvery colorations enhance distortion and confuse prey. Some species, like the butterflyfish, have false eye spots or black bands hiding the eyes. Predators cannot tell the head from the tail and become confused, allowing the fish time to escape. Other species take on the color pattern of toxic fishes even though they are not toxic. Some species of young batfishes even mimic floating debris like leaves, which may be unappealing to predators.
Poisonous stingers and spines
Some fishes have poisonous stingers to protect themselves from predators. Rabbitfish defend themselves with venomous dorsal, anal, and pelvis spines. Tangs (also called surgeonfish) are an important source of seafood on most tropical islands. They use sharp spines on their caudal fin and tail to slash and wound their predators. Angelfish look graceful, but these aggressive reef-dwellers use the short spines emerging from their gill plates for fighting.
Large schools of moving fish often confuse their predators and increase an individual’s chances of survival. Some species, like milkfish, travel in groups called schools for protection. Parrotfish are not well equipped to defend themselves. For protection, they graze among schools of venomous rabbitfish, which are seldom attacked by predators.
By drawing water into a special chamber near the stomach, pufferfish are able to “inflate” themselves two to three times their normal size-possibly too large for a predator to eat. They also have extremely toxic skin and tissues which, if eaten, are often fatal to predators.
Butterflyfish and triggerfish have slender bodies. If threatened, they wedge themselves between coral branches or into narrow crevices and erect fin spines so they are almost impossible to dislodge.