June 1: World Reef Day

The Threatened Rainforests of the Seas

Every year on June 1, World Reef Day draws our attention to one of the most spectacular natural wonders of our planet: coral reefs. This international day of action is meant to remind us of the extraordinary beauty and diversity these underwater worlds hold—and how acutely they are threatened.

From Stone Flowers to Living Architects

For centuries, people puzzled over the true nature of corals. As late as the 18th century, they were considered “stone flowers”—a romantic but completely false notion. It wasn’t until 1790 that the Italian zoologist Luigi Ferdinando Marsigli proved that they are in fact animals: tiny polyps from the phylum Cnidaria, related to jellyfish and sea anemones.

These unassuming builders accomplish amazing feats. Each polyp, no larger than a pinhead, filters plankton from the seawater while continuously secreting calcium carbonate. Since the polyps live in gigantic colonies of millions of individuals, massive calcium carbonate structures form over millennia—submarine mountains that rank among the largest structures on Earth created by living organisms.

Biodiversity Hotspots

Coral reefs cover less than one percent of the seafloor but are home to about 25 percent of all known marine species. These “rainforests of the seas” are home to over 4,000 species of fish, countless invertebrates, sea turtles, and marine mammals. A single reef can harbor more biodiversity than an entire tropical rainforest.
But reefs are far more than just habitats. They act as natural breakwaters and protect coasts from erosion and storm surges—a protective barrier of vital importance to over 500 million people. They also feed millions of people and generate billions in revenue annually through fishing and tourism.

The Silent Catastrophe

Today, these wonders of nature face their greatest threat: climate change. Even a temperature rise of just one to two degrees Celsius triggers what is known as coral bleaching. In this process, the stressed corals expel their symbiotic algae, which provide them not only with color but also with nutrients. Without these partners, the corals literally starve to death.

The figures are alarming: Since the 1980s, 50 percent of the world’s coral reefs have already disappeared. The Great Barrier Reef off the coast of Australia, the world’s largest reef, experienced the most severe bleaching event ever recorded between 2016 and 2017—more than half of the corals died.

But climate change is not the only threat. Pollution, overfishing, coastal development, and the increasing acidity of the oceans due to absorbed CO₂ are putting additional strain on the reefs. Scientists warn: Without drastic measures, virtually all coral reefs could be gone by 2050.

A race against time

World Reef Day reminds us that there is still time to act—though not much left. Marine biologists and conservationists around the world are working feverishly on solutions: from breeding heat-resistant coral varieties in laboratories to reintroducing healthy corals into damaged reefs.

But the key ultimately lies in the fight against climate change. Only by drastically reducing CO₂ emissions can we limit global warming and give the reefs a chance to survive. At the same time, local conservation measures are crucial: stopping overfishing, reducing plastic waste and chemicals, and promoting sustainable tourism.

Every World Reef Day is both a celebration of the beauty of these underwater worlds and a wake-up call. Coral reefs are indicators of the health of our oceans—and thus of the future of our entire planet. Their survival depends on our actions, and time is running out. What appears today to be a local environmental problem is in reality a global crisis that concerns us all.

The reefs have survived for millions of years—but whether they survive the Anthropocene, the age of humans, will be decided by “all of us” in the coming decades.