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Mucus balloons solve an ocean mystery

Click here for a high resolution photograph.

Some tadpole-sized ocean animals live in houses made of almost the very same stuff that leaks out of your nose when you have a cold. As researchers have just discovered, these mucus houses help solve the mystery of how creatures at the bottom of the ocean get enough food.

The house-building animals, called giant larvaceans are, in some ways, spiders of the sea. Every day or so they spin themselves a delicate, balloon-like house out of a substance that's very much like the mucus in our own bodies, according to Bruce Robison of the Monterey Bay Aquarium Research Institute.

Click here for a high resolution photograph.

Once they are abandoned, the houses, which are called "sinkers," fall to the seafloor. The sinkers can be about three feet across, and they work as filters while the giant larvacean lives inside. Large particles are trapped outside the sinkers and the smaller particles float in for the larvacean to eat. Larvaceans belong to a family of other filter-feeding animals known as "tunicates."

Lots of other small animals settle on the outside of the sinkers. Once the sinker gets too clogged for particles to float in, the larvacean abandons it and makes a new one. As the sinker drops to the seafloor, the other animals go along for the ride.

Click here for a high resolution photograph.

Robison and his colleagues have discovered that these other animals clinging to the fallen sinkers provide a major food source for the life living at the bottom of the ocean. The researchers describe their findings in the 10 June 2005 issue of the journal Science.

For years, scientists have puzzled over the question of how deep-sea life gets enough food, since most of the ocean's plants and animals live much closer to the surface. They had studied other types of particles falling to the seafloor, but there just wasn't enough to make up a full food supply.

Robison thinks that nobody appreciated the importance of the sinkers because these objects are so fragile that they would break apart before researchers could collect them in nets or other traps.

"The sinkers were apparent in older photos, but they just looked like snotty stuff down there. Nobody knew what they were looking at," he said.

Robison's team used underwater vehicles to monitor the numbers of sinkers off the coast of Monterey Bay, California. Over a period of ten years, they tracked how often larvaceans built new sinkers and how quickly the old ones dropped to the seafloor.

Finally, they had enough information to figure out that there are enough sinkers landing on the seafloor every day to provide an important food supply.