The mystery of how coral reefs thrive in "ocean deserts" has been solved, scientists say.
Reefs are among Earth's most vibrant ecosystems, yet they flourish in waters lacking nutrients – a phenomenon known as Darwin's Paradox.
A team found that sponges keep the reef alive – by recycling vast amounts of organic matter to feed snails, crabs and other creatures.
Writing in Science, they hope their findings will aid conservation.
Sponges recycle nearly ten times as much matter as bacteria, and produce as much nutrition as all the corals and algae in a reef combined, the scientists calculate.
They are the "unsung heroes" of the reef community, said lead author Jasper de Goeij, an aquatic ecologist at the University of Amsterdam.
"Up until now no-one has really paid sponges much attention. They look nice, but everybody was more interested in corals and fish," he told BBC News. Read more