Specialized Clams Serve as Sea Floor Eco-Engineers

In 2006, marine biologists Craig McClain and Jim Barry used the Monterey Bay Aquarium Research Institute's remotely operated vehicle to place 36 bundles of acacia wood on the sea floor of Monterey Canyon, 3,200 meters below the surface. Five years later, they retrieved the bundles. Now, a new release from the institute details their surprising findings.

Despite the bundles containing exactly the same type of wood and being placed on the seafloor at the same time in close proximity, there were huge differences in the numbers and types of animals from one bundle to another. It seems the biggest predictor of colonization, according to researchers, was the prevalence of wood-boring clams - which they called "ecosystem engineers" that make organic matter in the wood available as nutrients to other animals on the sea floor.

"Like oysters, beavers, and termites, these boring clams alter the landscape and provide new habitat for other species," said McClain, adding that these clams have specialized bacteria that helps them digest cellulose. "Without these wood-boring bivalves, the carbon energy in the wood would not be available to other species."

As the clams eat their way through a sunken log, they create small holes in which other animals can hide, their wood chips and feces provide food for a variety of smaller animals, and the clams themselves provide food for specialized predators.

In addition to an abundance of wood-boring clams, the rate at which a wood fall is colonized makes a big difference to deep-sea organisms living nearby. The faster that a piece of wood is colonized, the more quickly its organic matter is available to the rest of the ecosystem.

These differences in colonization from one bundle to another created a wide variety of habitats and animal communities over a relatively small patch of seafloor, adding to a growing body of evidence that sea floor animal communities often vary considerably over both space and time.

The team's research originally appeared in the journal Biology Letters.