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Planet Earth

Seafloor Food Source Identified

These tiny life-forms may explain how animals at the bottom of the ocean get enough to eat

By Megan Mansell WilliamsOctober 24, 2005 5:00 AM

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Among the ocean’s bizarre life-forms are tiny, tail-beating larvaceans. Resembling tadpoles no larger than a tube of lipstick, these drifting creatures weave self-made mucus into elaborate filters up to three feet across. The filters (called houses because the animal lives inside) let bite-size food in but keep out larger, suspended gunk. Even so, the filters clog every 24 hours or so, and the animals ditch them and start anew.

These abandoned houses, known as sinkers, may help solve a long-standing biological mystery: How do animals at the bottom of the ocean get enough to eat? For years, scientists have been unable to reconcile the nutritional requirements of crustaceans, sea cucumbers, snails, and tube worms nearly a mile beneath the surface with the amount of nourishment—microscopic organisms and other organic matter—that rains down from above. To measure the food, oceanographers put funnel-like sediment traps just above the seafloor to capture this falling debris. But because sinkers land randomly and can disintegrate on contact, sediment traps are unlikely to catch them.

Kim Reisenbichler, Bruce Robison, and Rob Sherlock, biologists from the Monterey Bay Aquarium Research Institute, collected more than 100 intact sinkers as they were still dropping and determined how much organic carbon each contained. They then analyzed 10 years of underwater video to estimate the number of sinkers that hit the ocean floor. From this, they calculated that sinkers contribute 7.6 grams of carbon per square meter of seafloor each year, an uncanny match to a food deficit found in a study using sediment traps.

“This is a pretty big contribution from what would be considered an obscure animal,” says Reisenbichler. He thinks sinkers may be important worldwide and that other unpredictable sources of sustenance will turn up in the future. “This is just one piece of the puzzle,” Reisenbichler says. “There are probably many other pieces yet to be discovered."

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