Water world

Large-scale forces shape local ocean life, global study shows

by Wendy Y. Lawton

The project began simply enough, with an idea and dives in the Gulf of Maine and the Caribbean. Now, after 14 years of research that sent him to six continents, Jon Witman's ocean odyssey is over. He swam among sharks in the Palau Islands, survived killer currents in the Galapagos, watched six-foot tuna hunt herring off the coast of Maine.

In the process, the associate professor of biology made an important finding: The variety of species found in a small patch of ocean is powerfully shaped by faraway forces.

Back in 1990, this was an emerging but untested idea in marine ecology. Most scientists believed that the number of species found in a particular stretch of shoreline, lagoon or reef was dictated largely by forces unique to that spot: the amount of competition among species, the intensity of predation, and the occurrence of hurricanes, landslides or other disturbances.

But a new theory was getting tossed around. Regional forces, such as climate change or egg-carrying currents, may also play a central role in local species diversity. After photographing and cataloguing nearly 3,000 species of sponges, corals and other shallow water ocean invertebrates, Witman and his team found that the theory proved true. Species diversity in local areas, no bigger than a half-mile square, was directly proportional to species diversity in that region, which can span thousands of square miles.

Their research, published last month in the Proceedings of the National Academy of Sciences, is the first global study to test this theory of biodiversity with entire communities of interacting species.

Witman, a professor in the Department of Ecology and Evolutionary Biology, called the findings "a wake-up call" for conservation efforts. Governments or nonprofits interested in maintaining biodiversity in the ocean or on land need to create a string of preserves or parks across a broad area in order to maintain biodiversity. Of particular importance, he said, is safeguarding "source areas" that act as wellsprings of eggs, seeds or vital nutrients, or that provide important habitat for critical species.

"As an ecologist, I have always enjoyed thinking on large scales," he said. "But after this project, I've realized that the oceans are even more interconnected than I realized. It has broadened my perspective."

Pulling off a global experiment isn't easy. To get a true snapshot of the diversity of shallow water invertebrates such as mollusks, barnacles and anemones, Witman and his collaborator, Ron Etter of the University of Massachusetts-Boston, knew they would have to get around. They pulled in marine scientist Franz Smith to assist.

Researchers sampled 49 sites in 12 distinct biogeographic regions - the Gulf of Maine, Iceland, the northeast Pacific, the Galapagos Islands, Chilean Patagonia, the Antarctic Peninsula, the eastern Caribbean, southwest Africa, southwest New Zealand, the Seychelles Islands, Norfolk Island and the Palau Islands. Alone or as a team, researchers would dive 30 to 50 feet below the surface. Then theyÕd take 18-by-24 inch photographs of a rock wall covered with the critters. The team shot 18 to 200 of these photo samples at each site.

The work could be difficult.

Smith, who sampled in the Antarctic Peninsula, had to dodge leopard seals and icebergs and brave subzero seas in a drysuit. Warmer climates had hazards, too. In the Palau Islands, the team took samples in a swarm of gray reef sharks circling a body length away. They dubbed the spot "Shark City."

At many sites, Witman struggled with cumbersome photo gear in quick-moving currents that threatened to sweep him out to sea.

And, of course, there was the sheer challenge of studying 1,500 photo samples and identifying more than 3,000 species. Witman spent nearly two years on this task alone, painstakingly examining slides, creating photo libraries and consulting invertebrate experts around the world. He spent summer days in his darkened basement, brought his data on vacation.

"Sometimes you'd wonder, 'Why am I doing this?'" he said.

But working in silent sunlit seas comes with priceless rewards.

In the Galapagos, Witman saw an enormous shadow pass along the rock wall he was photographing. He turned to see a 10-foot manta ray glide by like an otherworldly airplane. He saw sea lions bite the fins of sharks, just for fun. "Pretty cheeky," he said. In Palau, he swam between tiny rock islands blooming with Technicolor sponges and corals and spindly sea whips. The place, his favorite, is called "Wonder Pass."

"I feel privileged to work in the ocean," he said. "And I hope this project will help, in some way, preserve the diversity there."