Global Study Finds Local Management Key for Kelp Forest Health

In Gulf of Maine, Steneck says the seaweed
provides lobster habitat

WALPOLE, Maine — A half-century of global ocean research indicates local management is key to sustaining kelp forest health.

Kelp — large brown seaweed or alga — provides food or habitat for a number of species, including fish, sea urchins and lobster, says Bob Steneck, a University of Maine oceanographer and one of 37 scientists who took part in the international project.

Lead author Kira Krumhansl, an associate professor at Simon Fraser University in British Columbia, Canada, says understanding regional environments is central to maintaining the dense underwater forests.

“Each region is unique. In fact, each forest is unique,” says Krumhansl. “Managing stressors on local scales has a key role to play in maintaining the health of kelp ecosystems in the face of increasing global pressures.”

The research, published in the “Proceedings of the National Academy of Sciences,” is the largest study of kelp forests ever produced.

Scientists found that while kelp in 38 percent of the analyzed regions showed clear declines, there were regions where kelp has increased (27 percent) and others where no net change was observed (35 percent).

The range of trajectories observed across regions far exceeded a small rate of decline at the global scale (1.8 percent decline per year), according to the study.

Thus, while global factors associated with climate change affect kelp forests, regional effects vary depending on the kelp species, local environmental conditions and other stressors, including the combination of fishing and climate change.

In the Gulf of Maine, kelp forests are dynamic, says Steneck, a professor of marine biology, oceanography and marine policy based at the Darling Marine Center in Walpole, Maine.

In late 1980s, after harvesting of kelp-eating sea urchins ratcheted up in the Gulf of Maine, kelp forests began to flourish. In 2013, Steneck published research on this ecosystem “flip,” or chain reaction involving sea urchins, kelp and Jonah crabs.

Kelp forests, he says, are important to lobsters along the rocky Maine coast.

“They [lobsters] typically don’t like hanging out on a bare ledge that’s like a parking lot with nowhere to hide,” he says. “Kelp is a great habitat for lobster, so keeping track of kelp abundance is important. Fortunately, the coast of Maine is holding its own.”

Kelp also is a commercial crop being cultivated at sites along the Maine coast. Steneck says kelp forests help reduce the amount of carbon dioxide in the ocean so it can locally reduce ocean acidification.

Marine ecologist Andrew Rassweiler at Florida State University says kelp has a unique capacity to recover quickly from disturbances.

“A whole forest of giant kelp can disappear in a season, and it is tempting to overreact to such dramatic change,” he says. “This study presents important context for such changes; kelp can recover just as fast, and all these rapid local dynamics have added up to relative stability at the global scale over recent decades.”

Researchers analyzed a half-century of data contributed by academics, government agencies, volunteers and underwater scientists monitoring 1,138 ecosystem sites in 34 regions around the planet.

Despite amassing a comprehensive database of kelp abundances, data are still lacking from many regions worldwide. The lack of data hinders understanding of how kelp forests around the planet have changed and of their future trajectory, says co-author Jarrett Byrnes, assistant professor of biology-marine ecology at the University of Massachusetts Boston.

While Byrnes expected the study to yield all bad news, he says kelp emerged as a rock star of resilience.

“In many places, it’s managed to hold its own against environmental change. It’s quite exciting,” he says. “What is worrying, though, is that in one-third of the regions of the world we studied, even kelps have not been able to withstand the pressures of a changing world. Their loss may be a sign that we have finally tipped over the edge of a precipice.”

But, for the time being, Steneck says kelp forests along the coast of Maine are doing well and even increasing in places.

E-Edition Extra: View Seaweed Dragging in Norway video and other related links here.