UF professor receives $300,000 grant for marine ecosystem research

February 20, 2007

GAINESVILLE, Fla. — University of Florida zoology professor Brian Silliman likes to say that little guys can have big effects.

He’s talking about small grazers, 1- to 3-inch plant-eating organisms like snails and crabs that can kill off certain kinds of plant communities in marine ecosystems such as salt marshes. The effects of these organisms are most drastic when combined with other natural stressors such as drought, which reduce the ability of a plant’s immune system to fight diseases that attack plant tissue through scars left by the grazers.

Because these creatures kill plants indirectly by facilitating infectious disease, their effect on plant mass is much larger than what they actually eat.

Silliman has now been awarded a $300,000 grant from the Andrew W. Mellon Foundation to continue and greatly expand his research on this phenomenon.

Over the next three years, the grant will allow him to examine the relationships among small grazers, plant life, disease, heat and drought in many plant-dominated marine ecosystems around the globe. In addition to further study of salt marshes, Silliman will examine mangroves, kelp beds and sea grasses.

Before he is finished, he will have worked in Australia, New Zealand, the Netherlands, Argentina and Chile.

Though the facilitation of disease by small grazers has long been studied in agricultural and forest ecosystems, it has been overlooked in marine systems.

“This is the first demonstration in a marine system of this kind of mechanism,” Silliman said of his salt marsh research. His work has challenged a 50-year-old paradigm that only physical factors such as salinity and nutrients affect marsh grass growth.

Ecologists previously thought that the tiny snails in the salt marshes only ate dead grass, but they actually farm fungus on live grass leaves.

The small grazers create razor-like wounds in the grass, which allows growth-suppressing fungus to grow on the injured part of the plant. The grazers then eat the fungus, but the infection eventually can spread and kill the plant, especially when the plant is weakened by drought or heat.

“They had it backwards for nearly 50 years,” Silliman said. The snails weren’t simply attracted to dying patches of grass. They actually helped create them.

Once this phenomenon is better understood, efforts can be made to prevent the loss of plant life from getting out of hand. The most likely remedy would be to protect the small grazers’ predators, which would ensure a natural regulation of the grazer population. In the context of the salt marshes, an example of these predators would be blue crabs, which eat the tiny snails, Silliman said.

Silliman teaches his classes in concentrated four- to six-week chunks to enable his extended overseas research, he said.

“I was overwhelmed and humbled by the prestige of [the grant],” he said. “The foundation has a storied history of supporting ecological research, which goes on to advance theory in the field.”

Silliman’s grant-funded work will begin this spring in South America.