The lowly sponge credited with keeping world's coral reefs alive

AMSTERDAM, Netherlands, Oct. 7 (UPI) -- The mystery of how coral reefs, among Earth's most vibrant ecosystems, flourish in waters lacking nutrients is down to lowly sponges, European scientists say.

Sponges keep reefs healthy by recycling vast amounts of organic matter to feed snails, crabs and other creatures vital to the ecosystems, they said.

Sponges are filter feeders living in crevices of a reef, taking in plankton and organic matter released into the sea by corals.

By recycling nearly 10 times as much matter as bacteria and creating as much nutrition as all the other creatures in a reef combined, sponges are the "unsung heroes" of the ocean communities, Jasper de Goeij, an aquatic ecologist at the University of Amsterdam, said.

"Up until now no one has really paid sponges much attention," de Goeji told BBC News. "hey look nice, but everybody was more interested in corals and fish."

Waters around most coral reefs are lacking nitrogen and phosphorus, the building blocks of life, a fact first noticed by Charles Darwin during his 5-year voyage on the Beagle beginning in 1851.

That lack should hamper their growth, and the fact coral reefs thrive in such waters has been known as "Darwin's paradox."

The answer to the paradox, it appears, is as simple as the simple sponge, scientists said.

Sponges are big players in a reef's survival, and "they deserve credit for their role," de Goeji said.

"If you want a reef which is colorful and biodiverse, you need a 'sponge loop' to maintain it."