But for those of us who aren’t scientists, we may ask ourselves what is coral, and why is it important? We asked our Aquarists, who are working with academic institutions and aquariums across the world on Project Coral.
What is coral?
Did you know that coral is an animal and not a plant? The majority of corals are sessile, attaching themselves to the ocean floor so they are unable to move.
Most of the structures that we call coral are made up of hundreds of tiny creatures called polyps that grow together to form a colony. As they grow, they take up minerals from the water to build a hard skeleton – made of calcium carbonate which is similar to limestone. This builds the 3D structure that we call a coral reef.
There are over 2,000 identified species of coral, all with different characteristics of colour, size, shape and structure.
What does coral eat?
Most corals have a type of algae living inside them, in their tissue (called Zooxanthellae).
This algae uses energy from the sun to carry out photosynthesis – like plants on land – and this supplies the coral with up to 80% of its food. However, corals can also use their tentacles to catch plankton as a food source.
Where do corals live?
Corals can be found all over the world, forming coral reefs such as the Great Barrier Reef in Australia; the New Caledonia Barrier Reef in the South Pacific and the Florida Reef in the Atlantic.
Reef-building corals all need specific conditions to thrive, relying on a symbiotic relationship with algae. We usually think of corals in warm, clear and shallow water. However, there are also some cold water corals, including at home in the UK. Cold water coral reefs which sit around 400 metres beneath the surface, can be found near Scotland, such as the Mingulay Reef Complex in the Outer Hebrides.
How does coral reproduce?
Corals have two main ways of reproducing – spawning or brooding which is known as sexual reproduction. Or cloning themselves, known as asexual reproduction.
In asexual reproduction corals clone themselves, producing other polyps to build the colony. If a colony breaks, which may happen when a storm occurs, the individual coral pieces can also attach to new surfaces and survive to form multiple new colonies.
In sexual reproduction, when the conditions are most favourable, a phenomenon called broadcast spawning occurs. Over the course of days or weeks, a range of coral species will release their reproductive cells simultaneously – these look like tiny round balls in the water. The cells merge and fertilise to form larvae before finding a hard surface to attach to. This form of reproduction allows for genetic diversity and repopulates coral reefs.
As well as these amazing mass spawning events, some species can produce larvae internally, which they release into the water once developed. These species are called brooders.
Does coral breathe?
Sort of. Like all living beings, coral uses oxygen for its respiration and produces carbon dioxide. The algae that live within them then uses this energy in the photosynthesis process.
How long does coral live?
Some coral reefs have existed for thousands of years, however individual coral colonies can live for a few hundred years.
Different types of coral grow at different rates. Some branching corals can grow 10cm per year.
Does coral feel and think?
Fundamentally, corals are non-sentient and reactive beings without brains, eyes nor a nervous system.
However, coral is complex in other ways. They are also able to detect changes in their environment, such as daylength and temperature, which trigger mass spawning events.
What is coral most closely related to?
Corals fall into the category of Cnidaria, a group that includes jellyfish and anemones. All of these animals have stinging tentacles.
How do coral reefs form and how long does it take?
Coral reefs begin when coral larvae attach to rocks underwater along the edges of land. As the corals grow, reef structures begin to form in several different ways.
Fringing reefs are the most common type of reef and the fastest to form, taking roughly 10,000 years to grow. These are reefs that are close to the shore. They are usually narrow and in shallower lagoons.
Barrier reefs and atoll reefs take considerably longer to form. The timespan is dependent on their size, but can range from roughly 100,000 years to 30 million years.
The Great Barrier Reef as we know it developed during the last period of sea level rise which began around 10,000 years ago.
Why is coral important?
While coral may appear unassuming, it plays a vital role in marine ecosystems.
Coral reefs make up 0.1% of the ocean, but around 25% of sea life needs coral reefs for survival. This wide variety of marine life depends on coral reefs for food, refuge and reproduction, creating diverse ecosystems.
1 billion people around the world rely on coral reefs for food, income from tourism and coastal protection. Their 3D structure protects the shoreline from storms, waves, flooding and other natural phenomena, aiding humanity and protecting communities across the world.
Another interesting virtue of coral is that it possesses great potential in the medical field. Medicines and drugs are being innovated through compounds discovered in coral reefs which may help research in certain cancers and other diseases. It is believed that coral reefs still have a lot of undiscovered potential in this field and continuing research could unlock further importance in coral.
What is coral bleaching? Why does it happen?
When the conditions change in a coral’s environment, such as temperature, lighting or nutrients, they may expel the algae living in their tissues, causing them to turn white.
This is a process known as coral bleaching. When a coral bleaches, it loses its main source of food, however it does not die straight away. If conditions regulate quickly the algae can return, but if the extreme conditions persist, the coral will likely die.
This means that the climate emergency and the human activity that has caused it has a direct impact on corals and the ecosystems they live in. A warming planet means a warming ocean, and even small changes can prompt a bleaching event.
What are we doing to help coral?
Coral reefs are under threat. Human activities like pollution, fishing and the climate emergency mean we are losing coral reefs at an alarming rate.
Understanding coral reproduction and how reefs naturally rebuild themselves is key insight into how we can help preserve and restore coral reefs. This is why Project Coral at the Horniman is key.
In the wild, most corals reproduce over one or two nights a year during a mass spawning event. This means opportunities to study coral reproduction have been limited.
Project Coral is changing that. Replicating those environmental conditions in a laboratory setting means we can now induce corals to spawn more than once per year. Sharing the Horniman’s research with other institutions means we can open new avenues of research into coral reproduction, across multiple coral species around the world.
