Photo by Mark Wunsch

Oceanographers Carl Richter and Essam Saadallah use CaveCam to photograph hidden life (inset).

It all started five years ago, when a yacht off the coast of Israel broke loose from its moorings. “People were running all around the beach, shouting,” says oceanographer Claudio Richter of Germany’s University of Bremen. “We dove in and found that a chunk of reef coral had broken apart — and there were all these colorful sponges inside.” Richter and colleagues knew they were on the verge of solving a crucial mystery: What eats the very tiniest planktons in a coral reef?

In this murder case, there are no obvious suspects: the organisms lounging on the reef’s surface aren’t able to strain itty-bitty plankton out of the water. That’s why turning up filter-feeding sponges (creatures resembling splotches of paint on a painter’s palette) was so important. The researchers were not content to merely finger an unseen enemy — they wanted to prove that the innards of the reef housed a host of hungry sponges.

So Richter and Mark Wunsch, also of the University of Bremen, developed a device called the CaveCam: a camera mounted on a probe and fitted with a spherical lens to minimize distortion from the water. The scientists used CaveCam to examine crevices in reefs throughout the Red Sea. The device turned up vast quantities of sponges — enough to account for the lack of tiny munchables around the reef. The scientists looked at water before and after it entered the reef and found that after just a 5-minute journey past squadrons of sponges, 60 percent of the plankton had been eaten.

Richter and colleagues now intend to use CaveCam to see what plants and animals might be lurking in coral crevices throughout the world.