Teeming with wildlife, coral reefs take the top spot for being the most diverse marine ecosystem in the world. In fact, over a quarter of all marine organisms greatly depend on these reefs for food and shelter. That’s an amazing feat considering coral reefs make up less than one percent of the Earth’s surface. Due to its impressive biodiversity, these underwater structures are often called the ‘rainforests’ of the sea. Read on to learn 50 fun facts about the vibrant underwater world of coral reefs.
Fact 1: Coral reefs are neither plants or rocks, they’re animals.
- Due to their hardened appearance, they were initially thought to be rocks, but unlike rocks, corals are very much alive.
- Their attachment to the seafloor gives them plant-like characteristics, but unlike plants, they don’t make their own food.
Fact 2: Coral reefs are closely related to jellyfish and anemones.
- They are made up of thousands of tiny, soft bodied organisms called polyps.
- A single polyp attaches itself to a submerged rock on the seafloor, divides or buds, and multiplies into millions of clones creating a colony forming a single coral.
Fact 3: It takes around 10,000 years for a coral reef to form.
- The average growth rate of massive corals is only about 0.3 to 2 centimeters per year, while branching corals on the other hand grow to about 10 centimeters annually.
- Some of the existing coral reefs on Earth are over 50 million years old.
Fact 4: Coral reefs mainly rely on photosynthesis to survive.
- Microscopic algae called ‘zooxanthellae’ reside within the cells of the coral’s digestive cavity and are responsible for photosynthetic activities.
- 90% of a single polyp’s energy comes from its symbiotic relationship with the zooxanthellae, while the other 10% comes from hunting via tentacles at night.
Fact 5: Coral reefs support over 25% of all marine organisms.
- The reefs’ incredible biodiversity rivals that of the tropical rain forests of New Guinea and the Amazon.
- They serve as nurseries for large fish species, keeping juvenile fish safe from predators until they’re large enough to venture into deeper waters.
Fact 6: The coral reef’s vibrant colors come from microscopic algae.
- Individual coral polyps actually have translucent bodies.
- In every square inch of coral, millions of zooxanthellae reside and produce colorful pigments giving the coral its beautiful colour.
Fact 7: Hundreds of millions of people rely on coral reefs for protection and for their livelihood everyday.
- Coral reefs provide shoreline protection from storm damage, as well as food, tourism based jobs and even the development of new medicines.
- They contribute to about 375 billion U.S dollars to the U.S economy per year.
Fact 8: Coral reefs can only grow at a maximum depth of 150 feet.
- The corals’ photosynthetic ability is only limited to the ocean’s sunlit zones or Euphotic zones.
- Coral reef biomes require a constant temperature of 70 to 85 degrees Fahrenheit.
Fact 9: Corals are generally found in tropical waters.
- Tropical waters are located near or right at the equator where they are easily warmed up by the sun.
- Sunlight of course is an important requirement for the zooxanthellae’s photosynthesis to take place and for corals to grow.
Fact 10: There are 3 types of coral reefs: Fringing, Barrier reefs and Atolls.
- Barrier reefs are often found further out at sea, while Fringing reefs are relatively close to the shore.
- Since Atolls are usually large structures commonly found on the rim of a lagoon, they are often mistaken for islands.
Fact 11: Coral reefs are the most biodiverse marine ecosystem in the planet and are home to around 4,000 species of fish.
- Around, 800 hard coral species and hundreds more other species depend on coral reefs for food and shelter.
- The coral reef’s variety of life is so impeccable that there are usually more fish species inhabiting a two-acre area of healthy coral reef, than there are types of birds throughout the whole of North America.
Fact 12: Coral reefs improve the quality of water.
- They act as filters that trap floating debris, promoting cleaner surrounding waters.
- Interestingly, coral reefs grow larger in waters with strong currents and wave patterns, where nutrients are more readily available for the thriving ecosystem.
Fact 13: Coral reefs help stabilize the sea bed, enabling marine plants to survive.
- Seagrass, seaweed and other marine plants prevent the ocean bed from being eroded and lessen the effects of storm damage.
- Consequently, marine plants also serve as nesting grounds for fish, dugongs, manatees and other species.
Fact 14: Coral reefs can help treat cancer and other diseases.
- Recently, scientists have found out that many parts of a coral reef can be harvested to develop new medications for various diseases.
- According to the National Oceanic & Atmospheric Administration (NOAA), coral reefs have now become vital sources of new medicines for treating cancer, human bacterial infections, arthritis, heart disease, Alzheimer’s, and viruses.
Fact 15: 93% of Carbon dioxide in the atmosphere is absorbed by coral reefs, marine algae and vegetation.
- Enhanced global warming is caused by the increase in carbon dioxide concentration in the Earth’s atmosphere.
- The corals’ zooxanthellae algae remove carbon dioxide from the air through photosynthesis.
- Subsequently, large quantities of carbon dioxide are deposited to the ocean floor in the form of limestone excreted by coral polyps.
Fact 16: Climate change poses a major threat to coral reefs, with 1% of the world’s coral reefs dying each year.
- Greenhouse gases, derived from human activities, increase water temperature making mass bleaching and infectious diseases more prevalent.
- It also encourages rising sea levels, increased frequency of tropical storms and alteration of the world’s ocean circulation patterns, dramatically affecting coral reefs worldwide.
- Over the last 30-70 years 80% of coral in the Caribbean have been destroyed and 50% in Indonesia and the Pacific.
Fact 17: Ocean acidification alters the ocean chemistry, and a drop of just 0.3 in water pH is enough to reduce the corals’ calcification rates.
- Too much carbon dioxide, absorbed from the atmosphere, increases the pH of the oceans leading to ocean acidification and rising water temperature.
- This stresses coral reefs, causing them to evict their borders (zooxanthellae), leading to coral bleaching and eventual death.
Fact 18: The microscopic algae found in corals are not plants, they’re animals.
- There are different types of algae found on earth, from the microscopic ones to the larger ones with leaf like appendages that can reach several feet in length.
- Microscopic benthic diatoms typically live in coral reef ecosystems and are responsible for a living coral reef’s dense biomass.
Fact 19: Barrier reefs protect shorelines from storm waves. The coasts of Queensland, Australia, Fiji, Vanua Levu and Taveuni are all protected by barrier reefs.
- These reefs form a barrier that break apart strong waves, so they don’t hit the shore at full force and wash out the shoreline.
- This ensures the protection and survival of various types of animal and plant life.
Fact 20: Australia’s Great Barrier Reef is the largest reef system on Earth. It covers a whopping 133,000 square mile area, making it visible from outer space.
- The reef system is located in the Coral sea, off the coast of Queensland, Australia.
- It’s made up of over 1,050 islands, 2,900 individual reefs and stretches out to 1,400 miles or 2,600 kilometers in length.
Fact 21: The Great Barrier Reef is one of the “Seven natural wonders of the world”.
- Corals reefs may have existed for 500 million years, but the Great Barrier Reef is relatively young—It’s only 500,000 years old.
- The reef system is responsible for supporting a wide array of marine species and was selected as a World Heritage Site in 1981.
Fact 22: The Great Barrier Reef is equal in size to half of Texas.
- It covers an area greater than the size of the United Kingdom, Holland and Switzerland all combined.
- The reef system however is roughly the same size as Italy, Malaysia, Germany and Japan.
Fact 23: Half of the Great Barrier Reef is dead.
- 30% of the reef system’s corals died in 2016 because of mass coral bleaching, and another 20% was wiped out in 2017.
- This devastating blow has led to a large portion of the ecosystem, along the reef’s Northern coast, to become barren with only a slim chance of recovery.
Fact 24: The Mesoamerican Barrier Reef is the second largest reef system in the world. It stretches for over 550 miles.
- It stretches from Cancun to the Honduras.
- It also brings in a lot of tourism to Mexico, attracting more than 150,000 tourists per year.
Fact 25: The Red Sea coral reefs are very resilient, even in extreme temperatures!
- Situated between the Arabian and Sahara deserts, the Red sea coral reefs are known for their incredible heat tolerance and resilience despite extreme temperature changes.
- The reef system measures 1,200 miles in length and is home to 1,200 fish species, 10% of which are endemic to the area.
Fact 26: Belize’s Great blue hole was named a UNESCO World Heritage Site in 1996.
- This perfectly round coral structure was formed when an ancient cave collapsed.
- The hole is 1,042 feet wide, has a depth of 407 feet, and was first explored by Jacques Cousteau in 1971.
Fact 26: The Philippines is a marine biodiversity hotspot. However, 97% of the country’s reefs are under threat from pollution, overexploitation and destructive fishing practices.
- It’s located at the apex of the coral triangle, the epicenter for marine biodiversity and is considered as the Amazon of the sea.
- The country’s reefs provide livelihood and food security to millions of Filipinos, contributing an estimated amount of 1 billion dollars each year to the Philippine economy.
Fact 27: The Philippines’ Tubbataha reef was formed from multiple volcano eruptions 15 million years ago, and is only reachable by scuba diving boats, leaving from the province of Palawan.
- It’s considered as the best diving spot in the country and was recently nominated as one of the “Seven natural wonders of the world”.
- It’s home to 360 reef fish species, 360 coral species, 11 shark species, 13 species of dolphins and whales, birds and the green sea and hawksbill turtles.
Fact 28: Corals that build reefs are called “hard” or “reef building” corals.
- These hard corals secrete calcium carbonate underneath their bodies which serves as the base for the coral reef community.
- Stony skeletons are not only limited to the reef building corals. Organ pipe corals, blue corals, and the precious red corals have stony skeletons as well.
Fact 29: Soft corals like the Toadstool, Elephant ear, and the Tree coral resemble underwater trees.
- These soft bodied corals lack calcium carbonate skeletons but grow wood-like cores and fleshy rinds for support and protection instead.
- They are also called ahermatypic corals or non-reef building corals, and do not always possess zooxanthellae, allowing them to thrive in cooler and darker parts of the ocean.
Fact 30: There are 2 sub-classes of corals.
- ‘Hexacorallia’ include the hard corals whose polyps feature a sixfold symmetry.
- Blue corals and soft corals fall under ‘Octocorallia’, whose polyps have eightfold symmetry.
Fact 31: All corals are from the Phylum Cnidaria.
- That’s the same taxonomic group as the jellyfish and Nemo’s home which is the sea anemone.
- All Cnidarians have tentacles that contain cnidocytes which are stinging cells that aid them in capturing and subduing their prey.
Fact 32: Corals can reproduce in multiple ways.
- Interestingly, corals can be male or female or both, and they can also reproduce both asexually and sexually.
- Asexual reproduction in corals is important for increasing the coral colony, while sexual reproduction plays an important role in increasing the coral species’ genetic diversity.
Fact 33: Corals can reproduce asexually.
- In Asexual reproduction, polyps and colonies are created that are clones of each other.
- When a coral polyp reaches a certain size, it divides, creating a genetically identical new polyp in a process called Budding.
Fact 34: Corals can reproduce sexually.
- Sexual reproduction occurs in corals when eggs are fertilized by sperm from a neighboring colony, which then develops into a free-swimming larva.
- The 2 types of sexual reproduction in corals are internal and external.
Fact 35: Individual coral polyps are generally very small: sometimes less than half an inch in diameter.
- Most hard or stony corals have teeny tiny polyps with diameters of just 1 to 3 millimeters.
- Mushroom corals have the largest polyps, which can measure up to over 5 inches in diameter.
- As the polyps grow into reefs, they provide structural habitats for thousands of vertebrate and invertebrate species.
Fact 36: Corals just like trees have annual rings.
- Like terrestrial tree trunks, a coral’s cross-section has growth rings that can be used to determine its age.
- Information on factors affecting coral growth including temperature, sunlight, and nutrients can be derived from a coral’s growth rate too.
Fact 37: You can find corals at depths of 6,000 meters.
- Deep-sea corals include both stony and soft corals which you can find at underwater peaks called seamounts.
- Since they don’t have microscopic algae living inside their cells, they don’t require sunlight or warm waters to survive.
Fact 38: Crown-of-Thorns sea stars prey on corals and they can grow to 80 cm across, eating 10 square meters of corals each year.
- These type of sea stars are voracious predators found in many parts of the Pacific Ocean.
- When uncontrolled, increased populations of these predators can result in the coral reef being covered with thousands of COT’s that feed on the corals.
Fact 39: Corals are capable of forming symbiotic relationships with other animals.
- In some coral colonies, you’ll find crabs and shrimps living within the coral branches.
- These tiny residents defend their coral homes from predators using their pincers.
Fact 40: The colorful Parrotfish “eats” corals.
- In their search for seaweed, Parrotfishes will usually bite off chunks of corals.
- These herbivores would then excrete the digested coral remains as sand.
Fact 41: Increased ocean acidity can dissolve coral reefs around the world.
- When ocean acidification intensifies, it can break apart existing coral skeletons and dissolve them, threatening the foundation of the reefs.
- Scientist predict that by 2085, theEarth’s oceans will be too acidic for corals to survive, and coral reefs around the globe will start to dissolve.
Fact 42: The Caribbean coral reefs are dying. In fact, the Caribbean has lost 80% of its coral reefs in the past years.
- Average life on the Caribbean reefs has declined to just 8% from a 50% coral reef cover in the 1970s.
- Although coral reefs draw in a lot of tourism, it’s also one of the main causes of reef destruction across the Caribbean.
Fact 43: Coral reefs cover less than 1% of the ocean floor.
- All reefs combined would cover an area of about 110,000 square miles.
- That’s only about the size of Nevada, USA.
Fact 44: There over 2,500 species of corals.
- Around 1,000 are species of reef-building corals.
- The rest are soft corals.
Fact 45: Clownfish are common residents in coral reefs: 28 kinds of them in fact.
- These colorful fishes became a hit all thanks to the animated film “Finding Nemo”.
- Clownfish have white stripes across their bodies, and their bodies can be orange, red, yellow, blue or black.
- Interestingly, all clownfish eggs hatch as males, and when the female alpha in the group dies, the dominant male undergoes a sex change and turns into a female.
Fact 46: There are 52 species of venomous sea snakes living in coral reefs.
- Sea snakes can reach lengths of up to 3 to 5 feet.
- Sea snakes have neurotoxic venoms, and common symptoms of sea snake bites usually begin after the 3-hours.
Fact 47: There are 5 types of reef sharks.
- These are: Blacktip, Gray, Caribbean, Whitetip, and Silvertip reef sharks.
- Reef sharks are smaller than pelagic sharks, reaching only 5 to 10 feet in length, but they are the apex predators on the coral reefs.
Fact 48: Coral reefs are home to 7 types Sea Turtles.
- There are seven species of sea turtles found in the Earth’s oceans: Leatherback, Loggerhead, Hawksbill, Green turtle, Kemp’s Ridley, Olive Ridley, and the Flatback sea turtle.
- Among these 7 species, 6 are listed as endangered of threatened.
Fact 49: The world’s coral reefs are under threat and over a fifth of the world’s coral reefs have already been destroyed or severely damaged.
- Coral reefs face many threats from local sources, including physical damage or destruction, pollution originating from land-based activities, coral harvesting, and overfishing.
- Other climate impacts, such as rising sea levels, increased frequency and intensity of tropical storms, and altered ocean circulation patterns can also affect coral reefs.
Fact 50: Artificial reefs can help rebuild our oceans’ coral reefs.
- Not only do artificial reefs help enhance marine wildlife, they also aim to prevent coastal erosion, by breaking apart waves from shallow areas.
- One unique artificial reef is the Neptune Memorial Reef in Key Biscayne, Florida. It’s an underwater Atlantis built to be like a cemetery.