This is why coral reefs are so vital for the planet

Beneath the ocean’s surface, colourful islands covered in algae are working hard to help the marine environment.

Although they look more like plants or rocks, corals are animals that are essential for the planet. Their bright, colourful exterior hides numerous complex processes that help build and maintain one of the most important ecosystems in our oceans.

So it’s crucial we preserve the world’s reefs from the increasing threat of warming ocean temperatures, pollution and mass bleachings.

As the chart above shows, more than a quarter of the planet’s reef-building corals are either vulnerable or endangered.

Natural protection

Ocean reefs act as a buffer, protecting shorelines and coastal communities from the impact of big waves, storms and hurricanes as they make landfall. These natural barriers help prevent loss of life, protect property – such as homes, ports and marinas – and guard against shoreline erosion.

But while reefs protect waterfront developments, over time, excessive shoreline construction and dredging, along with sewage and polluted runoff from agriculture can leave them damaged. When coral dies, there is a domino effect that disrupts the marine life that lives on, in or around it.

Living corals make a skeleton underneath themselves, which they leave behind as they grow towards sunlight, creating habitats for marine organisms, like sponges, clams and snails. These smaller organisms attract bigger fish looking for food, which in turn fall prey to even bigger fish and marine mammals.

As a valuable source of nitrogen and other essential nutrients, ocean corals support entire marine food-chains, which depend on them for survival.

They also absorb and store harmful pollutants, such as carbon, in the same way trees remove CO2 emissions from the atmosphere. This process regulates carbon levels in the waters around reef systems, providing an environment for microorganisms to thrive.

Finally, corals recycle matter and nutrients from broken-down elements, generating new life from old in a process that self-perpetuates the reef’s ecosystem.

Bleached white

But such ecosystems are delicately balanced and easily disrupted. Colourful coral formations are highly sensitive to changes in water temperature, light conditions or nutrients, and can eject the algae that live and feed on them – a phenomenon known as bleaching.

Stressed coral turns white, leaving it vulnerable to disease, and if the algae loss occurs over a lengthy period, the reef could eventually die. When the algae disappear, creatures further up the food chain disappear, too.

Climate change makes extreme storms and mass bleachings more frequent and more severe, turning some once-flourishing marine environments into underwater deserts.

Australia’s Great Barrier Reef has declined by 50% since 1985, due to storm damage, coral bleaching and waves of crown-of-thorns starfish suffocating the coral.

Warming ocean waters prevent corals laying down their calcium carbonate skeleton, which inhibits the growth essential for a healthy reef ecosystem.

Besides climate change, destructive or excessive fishing, coastal development and ocean pollution all add to the threat faced by ocean corals.

According to research from the World Resources Institute, more than half of Earth’s reefs could be under threat by 2030, and unless urgent action is taken on a grand-scale, they could disappear completely by mid-century.

Their loss would be devastating for the planet, as well as for the communities that rely on coral reefs for employment and tourism.

The long-term solution lies in addressing the underlying causes of climate change - but this is not a quick-fix.

In the meantime, scientists like Kristen Marhaver, working at the Caribbean Research and Management of Biodiversity (CARMABI) Research Station in the Caribbean, are trying to rebuild reefs by growing baby corals.

She is part of a team trying to uncover the secrets of coral reproduction, which could help regenerate reefs under threat.