Coral reefs provide some of the most fascinating and colorful aquatic life in the world’s oceans. Although coral reefs may look like rocks or plants at first glance, they are sea creatures, just like the fish and sharks that surround them.

Here are eight coral reef facts to help you understand more about these beautiful sea creatures.

Coral Reefs are Related to Jellyfish and Sea Anemones

jellyfish swimming in water

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Corals may look like static sculptures at first glance, but they are living creatures resembling polyps. Coral reefs, jellyfish, and sea anemones are part of the same class of sea creatures, Anthozoa, in the Cnidaria phylum. A coral reef isn’t one organism. Coral reefs are communities of connected entities.

Separate corals that join with one another to form a reef, or colony, of polyps, joined by calcium carbonate. Coral reefs are usually comprised of clustered polyps from stony corals.  

A polyp is a sea creature with a body shaped like a vase. There’s an open mouth at one end, and that end is surrounded by tentacles. You may have seen the tentacles on polyps move and snatch small sea creatures.

The tentacles have nematocysts, or stinging cells, that snatch up edible organisms. Polyps have digestive organs, as well as reproductive tissues.

A pedal disc holds a solitary polyp's aboral end to the substrate. The colonies of polyps you're used to seeing in underwater documentaries are connected polyps.

Corals have a mineral skeleton, which sea anemones lack. The exoskeletons protect the coral against harmful elements. Coral reefs prosper in clear, warm, and shallow water.  

Coral Reefs Help the Economy 

Coral reefs have a monetary worth of between 30 and 172 billion dollars. The reefs provide tourism jobs, shoreline protection, food and medicine for people in many parts of the world. Diving tours, hotels, bars, restaurants and fishing trips near coral reefs bring in millions of tourism dollars yearly.

Commercial U.S. fisheries earn more than $100 million a year from operating near coral reefs. Half of the fisheries managed by the federal government need coral reefs and their habitats for at least some of their growth.

Corals and Algae Have a Symbiotic Relationship

Corals are aquatic animals, but they do require photosynthesis to stay alive.  Zooxanthellae (microscopic algae) live in the tissues of reef-building corals. Coral gives the algae the compounds it needs for photosynthesis, and the algae produce oxygen so the coral can rid itself of waste products.

Zooxanthellae produce amino acids, glucose, and glycerol, which coral uses to make calcium carbonate, fats, protein, and carbohydrates.  The beautiful colors you see in most stony coral also come from zooxanthellae.

Bleached, or stark white coral, is a result of physical stress. Corals shed their algal cells and turn white due to excessive stress. Bleached coral will die if they don't get zooxanthellae for a long time.

Reef coral reacts to its environment like plants due to their interaction with zooxanthellae. Coral must live in clear water since algal cells require light for photosynthesis.

Corals Eat Plastics People Have Thrown in the Ocean

A 2017 study showed that corals eat microplastics in the ocean, mistaking them for food. Researchers discovered that coral like the taste of the plastics. The corals in the experiments liked unfettered microplastics, not ones covered with bacteria.

Humans have made plastics that are tasty to coral reefs. Corals don’t have eyes, so they use their tongues, or chemosensors, to decide what to eat. According to a Duke University study, coral will eat raw plastic, not coated plastic or sand.

Although chowing down on plastic is a danger to coral, it’s not as bad as acid in the ocean, coral bleaching and extensive fishing.  

Overfishing, pollution and new species invading coral-heavy waters pose a threat to coral reefs. Many reefs have been destroyed while others have been seriously damaged.

Coral Reefs Provide a Home for Ocean Creatures

One of the most interesting coral reef facts shows that these sea creatures house and protect thousands of other ocean-dwelling species. Coral reefs provide food and shelter for fish. Reefs give fish a place to mate and reproduce. Young fish hide safely in the coral reefs until they’re ready to venture into the ocean.

Coral reefs have more biodiversity than tropical rainforests, and they are believed to have the highest biodiversity on earth. Coral reefs occupy slightly less than one percent of the ocean floor but contain more than a quarter of marine life.  

Diverse ecosystems can deal better with climate disturbances and outside forces. Humans also receive greater benefits from biodiversity than from regions with few species.

Beautiful spotted and striped fish swim around coral reefs. These fish eat algae and protect the reefs from being victimized by predators. Sharks and groupers also protect the reefs from being damaged by enemies.

Mollusks, sea squirts and tunicates (salps) eat phytoplankton and help clean and filter the water. Sea sponges provide a home for young fish, crustaceans, and marine worms in their canals. These sea animals also take nutrients from the water and produce waste to feed other species. Fish and sea turtles eat sponges.

Many Medicines are Derived from Coral Reefs

The Chinese people have often used seahorses from coral reefs as a treatment for skin diseases and respiratory problems since the 14th Century. Today, coral reefs are sources of medicines for cancer, Alzheimer's, heart disease, bacterial infections, and other health problems.

AZT, a medicine that slows down the HIV virus and reduces the chance of full-blown AIDs came from a sponge species from coral reefs in the Caribbean. Extracts from reef sponges are also used in the anti-cancer drug, Ara-C.

There are Four Main Types of Coral Reefs

live corals

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There are four basic types of coral reefs found around the world are barrier reefs, fringing reefs, platform reefs, and atolls.

Fringing Reefs

Fringing reefs are the most common reefs in the world. These reefs develop by the coastline of continents and islands. A shallow, narrow lagoon separates them from the shore.

Barrier Reefs

Barrier reefs are formed parallel to the coastline and separated by deep, wide lagoons. The reefs reach the water’s surface at their shallowest point and prevent navigation. Australia’s Great Barrier Reef is the most famous barrier reef in the world.

Some coral reef facts about the Great Barrier Reef:

  • It is one of the Seven Wonders of the World
  • You can see it from outer space
  • It has 1625 fish species
  • It’s the largest living structure on earth
  • It attracts two million visitors each year

The Great Barrier Reef Foundation provides information about the Reef and all of the aquatic life surrounding it. The Foundation is dedicated to preserving reefs in Australia and throughout the world.  

Platform Reefs

A platform or patch reef is located on continental shelves and is sometimes found behind barrier reefs. These reefs may be elongated if they’re located on a sandbank. An elongated reef may be created by the rise and fall of tides. Torres Strait, a reef between New Guinea and Australia, is shaped like a boat and was formed by such currents.

Asymmetrical currents create horseshoe reefs. The Low Islets, in Southeastern Australia, have sand cays on both of its downward wings.


Circular or continuous atolls extend around a lagoon, even though they are not connected with a central island. Atolls may form from fringing reefs around island volcanoes, and the island may erode or disappear below sea level.  

The most famous atolls are located in the Indian Ocean and the South Pacific.  The Cook Islands, the Marshall Islands, and French Polynesia are atolls in the middle of the ocean. Atolls in the Indian Ocean exist around the Cocos Island and the Seychelles. The Maldives has 26 atolls.  

Corals Repro​​​​duce in Several Ways

blue corals

image source: Unspalsh

A coral can be male, female or have characteristics of both sexes. Corals reproduce sexually or asexually. Sexual reproduction starts new colonies and creates diverse-looking corals. Asexual reproduction expands the colony.

Sexual Reproduction

Eggs from one coral reef colony become larva after being fertilized by sperm.  Larvae find a substrate to grow on, and in a few hours to a few weeks, the larvae turn into polyps.

Many stony corals spawn externally, or outside the body — colonies of coral release bundles of eggs and sperm. (There is only one bundle for each polyp.) The bundles float to the surface, and the spawning usually occurs once a year, at night. In some areas, the spawning is meant to affect all species in a particular area.

Certain corals brood eggs into a polyp body, then release sperm in the ocean. Polyps with eggs take in the sinking sperm. The fertilization takes place inside the polyps. Brooder may reproduce several times a year according to the moon’s cycle.

Asexual Reproduction

Asexual reproduction occurs through fragmentation or budding. When a segment of a colony breaks off and becomes a new colony, it’s called fragmentation. An accident, such as damage from fishing equipment or a storm may cause fragmentation.

Budding occurs when a coral polyp may divide into new, identical polyp when it becomes a certain size.