For centuries scientists, even Darwin, couldn’t make sense of it: Tropical water contains so few nutrients, you can see right through it. And yet coral reefs are oases that support about a quarter of all known species on Earth.

How could that be?

The answer to this paradox, in part, is sugar.

We tend to think the ocean tastes salty. But shaken, stirred and dissolved in seawater are microscopic morsels of sugars and carbs, known as dissolved organic matter. This dissolved substance makes up most of the organic material in the ocean. And it’s especially abundant around coral reefs.

“Imagine all these sugars dissolved into the ocean: If no one can use them, they might as well not be there,” said Michelle Achlatis, a researcher at the California Academy of Sciences.

But then there’s Cliona orientalis.

This filter-feeding sponge lives on coral reefs in the Indian and Pacific Oceans, straining tiny plankton to eat as it sits in the water. But its filtering cells also sip sugars from seawater.