Coral reefs first started appearing on Earth around 500 million years ago. Although coral reefs only occupy about 0.1% of the world’s oceanic area, they are believed to be the ecosystem with the highest biodiversity on the planet, providing a home for approximately 25% of all marine species. When visiting the Two Oceans Aquarium, be sure to stop by our beautiful coral reef exhibit. It is one of the first you will encounter. Also, peer into the amazing zooxanthellae exhibit. Here you will see how corals and zooxanthellae, brightly coloured microscopic algae, live together in a symbiotic relationship of colour and movement.
Fun facts about coral reefs
- Coral reefs are known as the “rainforests of the sea” because of their incredible biodiversity.
- Coral reefs are natural water filters: by consuming particles that don't dissolve in water, corals prevent pollutants from dirtying the ocean.
- Coral reefs are the largest non-human-made structures on Earth.
- Coral reefs are found in both warm- and cold-water oceans.
- Coral reefs are animals, not plants! They are actually related to jellyfish and anemones.
- They are one of the slowest growing organisms on earth - coral grows an estimated one cm per year.
- They offer protection: coral reefs are natural barriers against tsunamis and hurricanes.
What is a coral reef?Before we can talk about what coral reefs are, we have to talk about the animals that are responsible for building them – corals! There are two types of corals: hard coral and soft coral. Hard corals are responsible for building coral reefs, while soft corals are flexible organisms that mostly resemble plants or trees. Individual corals are known as polyps. Hard coral polyps extract calcium carbonate from seawater and create hard external skeletons. Hard coral polyps live on the exoskeletons of their predecessors and add to these structures as they grow. Combined in a colony, these skeletons form what we know as a coral reef. Coral reefs support a myriad of aquatic life by acting as productive nurseries for many fish species, as well as providing homes and sustenance for other animals.
Habitats and lifestylesIt is estimated that there are around 6 000 species of corals, found in both warm and cold water. They exist in an array of shapes, sizes, and colours. The biggest coral reefs are found in the clear, shallow waters of the tropics. The Great Barrier Reef, the largest reef system in the world, is located off the coast of Australia and stretches across 2 400km. Corals belong to the same phylum as jellies, anemones, hydras, sea pens and blue bottles. Some corals feed by catching small prey, but most are reliant on the algae (zooxanthellae) that live inside the coral polyp’s body and generate energy through photosynthesis. The polyps and the algae have a symbiotic relationship: the algae provide the polyps with energy, and the polyps provide the algae with a home and carbon dioxide. The zooxanthellae also give the coral its vibrant colours.
Why are coral reefs important?Coral reefs are some of the most diverse and valuable ecosystems on Earth, responsible for marine ecosystem health and biodiversity. They provide food, shelter and spawning grounds for fish and other marine animals. It is estimated that coral reefs support around 4 000 fish species, to name a few. Through their symbiotic relationship with zooxanthellae, coral reefs produce a tremendous amount of oxygen which is vital for ocean and planet health. Coral reefs protect coastlines against storms and erosion, as well as provide jobs, food, and medicines. According to the UN, over half a billion people are dependent on reefs for food, work, and coastal protection.
Climate change in coral reefsThe oceans are experiencing an increase in temperature due to climate change. The change in temperature, nutrients, and light stresses the coral, which causes them to expel the algae that live symbiotically within their bodies. This is called “coral bleaching”: although a bleached coral is still alive, the stress can eventually lead to death. With the algae gone, the coral no longer has its primary source of food, and it becomes more vulnerable to disease. Primarily due to rising temperatures, between 30% and 50% of the world’s coral reefs have been lost in the last 40 years, with 14% dying between 2009 and 2018. We can all make a difference by supporting the drive against climate change. Conserving water, supporting ecologically sound and organic farming methods and using less energy can contribute to the preservation of coral reefs.