By now, you've probably heard that at least 90 percent of the Great Barrier Reef has been affected by a global bleaching event. But these "rocks" on the seabed play a key role for life in oceans - and for people, too.
The world's largest coral reef ecosystem is dying at alarming rate - and there are plenty of reasons to care.
The Great Barrier Reef is home to 600 different types of hard and soft corals and thousands of animal species, including threatened species. No other UNESCO World Heritage site boasts such biodiversity.
The reefs provide key protection for the shoreline - without it, surrounding villages would fall into the ocean. Reefs dampen the effect of storms from the open sea and reduce the force of waves, preventing the erosion of shorelines.
But 93 percent of the reef within this rich ecosystem has been affected by coral bleaching - a deadly phenomenon taking place due to environmental changes over the past decades, such as warmer water temperatures and ocean acidification.
With the Great Barrier Reef at risk, the survival of innumerable lives - from anemones to humans - is also in danger. And some experts even believe that unless drastic action is taken, coral reefs could disappear by the end of this century. But there is still hope.
Outstanding rich ecosystem
According to World Wildlife Fund (WWF), coral reefs are home to a quarter of all marine life on the planet. They support more species than any other marine environment, despite covering less than 1 percent of the Earth's surface.
Around 3,000 coral reefs are distributed along the Great Barrier, which covers an area of around 344,000 square kilometers along a wide range of zones: from deep ocean waters to shallow inshore areas.
More than 1,500 species of fish, 3,000 species of mollusk and some 215 species of birds - together with sponges, anemones and marine turtles, among others - live together in the Great Barrier Reef.
The interconnectivity among this diversity of species and habitats make the Great Barrier Reef one of the richest and most complex natural ecosystems on earth - and one of the most significant for biodiversity conservation, according to UNESCO.
'10 cyclones at once'
Coral reefs and their habitats face several threats, among them destructive fishing practices, unsustainable tourism, pollution and climate change.
The ARC Centre of Excellence for Coral Reef Studies points out that the Australian government has long blamed climate change as the biggest threat to the Great Barrier Reef - and to its ecosystem, and the people depending on it.
And the situation is worsening every day. A study presented April 20 by the coral center revealed that 93 percent of the Great Barrier Reef has been affected by coral bleaching.
"We've never seen anything like this scale of bleaching before," said Terry Hughes, coordinator of the National Coral Bleaching Taskforce. "In the northern Great Barrier Reef, it's like 10 cyclones have come ashore all at once."
Coral bleaching is occurring mainly due to warmer sea temperatures - which explains why reefs further south in the southern hemisphere have lower levels of bleaching. According to the researchers, over recent months water temperatures in southern regions have been close to normal summer conditions.
Corals can only survive within a narrow range of ocean temperature. They exist based on symbiosis with algae that grows within their tissues - but as oceans warm, corals expel this algae. This causes coral bleaching - and coral death.
Divided we fall
Coral reefs provide shelter and food to various organisms, which form a complex food web. Coral reef fish, for instance, depend on coral for food. Predatory fish then depend on them. Whales and dolphins are also predators - making survivial a difficult task for them once the fish are gone.
Six of the world's seven species of sea turtle live in the Great Barrier Reef, including the critically endangered Hawksbill turtle. These animals - which are key for healthy marine ecosystems - are also highly dependent on the coral reefs, as they feed mainly from sponges, found in reef crevices.
Humans, too, will suffer the consequences of bleaching coral reefs. Great Barrier Reef tourism generates at least 5 billion Australian dollars a year (around 3 billion euros), and employs nearly 70,000 people, the coral center wrote.
Globally, half a billion people are estimated to benefit from the productivity and protection of coral reefs, according to the United States National Oceanic and Atmospheric Administration.
In addition, coral reefs serve as buffer for human settlements onshore. "A reef dampens the effect of a storm coming in from the open sea, diminishing the force of the waves," said Peter Sale, an expert on coral reef ecology and management. "Without reefs, you get erosion of shorelines and villages falling into the ocean," he told DW.
The future of the reef
This is not the first time scientists have observed coral bleaching at the Great Barrier Reef. Two mass bleaching events already occurred in the area - in 1998 and 2002, Hugues said.
Despite the northern part of the Great Barrier being affected as it never has been before - including the difficult recovery this implies - more modest bleaching observed in elsewhere provides hope for recovery.
"Many of the corals there are more moderately bleached, so we expect that most of them will survive and regain their normal color as temperatures drop over the coming months," Hugues said.
In order to prevent further coral bleaching, the coral center urges a reduction in global carbon emissions and improving the quality of water flowing to the reef. Management of fishing, coastal development, pollution and shipping will determine the future resilience of the Great Barrier Reef, the coral center said.
Sale believes if we start taking better care of the reefs, a future recovery may be possible - and we'd better act now.
"They are the richest ecosystem in the ocean in terms of how many different kinds of plants and animals live there," Sale said. "They are arguably as rich as or richer than the rainforests on land."
"We shouldn't throw away something like that."