Sea Critters’ Feces Clean Air, Study Says

The fast-sinking feces of an obscure sea creature play a significant role in removing the greenhouse gas carbon dioxide from the atmosphere, according to a new study.

Salp -- transparent, jellylike animals about the size of a human thumb -- are filter-feeders that spend their lives vacuuming up phytoplankton from the ocean’s surface.

The phytoplankton assimilates carbon dioxide from the air and water as it grows. After salp eat the phytoplankton, they excrete the gas trapped in dense fecal pellets that quickly sink to the ocean floor. There in the deep, the carbon dioxide cannot reenter the atmosphere.

A team led by marine biologists Laurence P. Madin of Woods Hole Oceanographic Institution and Patricia M. Kremer of the University of Connecticut found a “hot spot” off New England where huge swarms of a particular salp species, Salpa aspera, had been observed on four occasions over the last 30 years.

In the May issue of Deep Sea Research, the team describes a swarm they encountered in 2002 that covered about 38,600 square miles -- larger than Indiana.

Studying the rates at which the salp ate and defecated, the team calculated the swarm could be dropping as much as 4,000 tons of carbon dioxide to the ocean floor each day.

For comparison, an SUV can emit about 7 tons of carbon dioxide each year.

Madin said that though salp were not going to solve global warming, further study of other hot spots would help scientists better understand salp’s contribution to the carbon gas cycle.

The team is studying another closely related species of salp off Antarctica.

Swarms there are thought to be the largest in the world and may be expanding as temperatures rise.