For scuba divers interested in tropical biodiversity, coral reefs were always the place to go. But a new study has found that tropical waters can also harbor kelp forests, traditionally thought of as the marine biodiversity hot spots of cooler temperate zones. The discovery suggests that kelp forests may be more resilient to climate change than previously believed.
"This is a revolutionary new view of marine biogeography. The idea that kelp forests occur extensively in all latitudes is simply staggering," says marine biologist James Estes of the University of California, Santa Cruz.
Kelp forests are marine communities that provide shelter and food for thousands of species as diverse as the tiny sluglike nudibranch and the inquisitive sea otter. Until now, scientists thought kelp forests could not develop in the tropics because kelp depend heavily on cool, nutrient-rich waters. Conservationists worried that kelp forests were threatened as the surface temperatures of the oceans go up.
To explore the kelp forests' future, ecologists Michael Graham of Moss Landing Marine Laboratories in Moss Landing, California, and Brian Kinlan of the University of California, Santa Barbara, developed a mathematical model to determine whether some tropical regions might provide the light, nutrients, and low temperatures that kelp forests need to survive. The model predicted more than 23,000 square kilometers of cooler tropical waters around the world, where sunlight and nutrients were still intense enough for kelp to flourish. Most were at deeper levels than those where reefs are found. With a team of research divers, they then surveyed a predicted kelp-rich area in the Galápagos.
As the researchers report online this week in the Proceedings of the National Academy of Sciences, their model was correct: They found a kelp forest. "I dropped down 20 meters, and it was like traveling from the tropics to California," says Graham. "There were abalone, sea hares, decorator crabs, and sheepshead fish, ... all just below the Galápagos environment where iguanas were swimming overhead."
The newly discovered forests haven't been properly studied for biodiversity yet, but they may host populations as diverse as those in their temperate counterparts, the researchers say. That's good news, they suggest: As temperatures rise, kelp forests may simply go deeper, and they might take the animals they shelter with them.
But some are less optimistic. "Just because kelp forests can exist at depth doesn't mean that global warming will not put these ecosystems at increased risk," says biologist Allison Alberts of the San Diego Zoo's center for Conservation and Research for Endangered Species in California. "The kelps may adapt, but the species dwelling in them may not."