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September / October 2006 Cover


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Green crab

 


A Balancing Act
A leading UMaine marine scientist says better management is needed to save the world's oceans that are drastically out of sync

About the Photo: Invasive species like the green crab are just one of many problems facing the health of marine ecosystems and the sustainability of marine fisheries. By feeding on native shellfish and other organisms, and competing with native crabs and lobsters for food and shelter, green crabs and their imported brethren have been a scourge along both coasts of North America.
 

Sidebar

Lost World
More than 20 years ago, in an attempt to assess the ecological impacts of the cod's disappearance in the Gulf of Maine, Bob Steneck spent months monitoring predator-prey interactions along an undersea mountain known as Cashes Ledge.

Sidebar

Dynamics of Diversity
From microscopic mudworms to 100-pound cod, all marine organisms are part of a complex web of interdependence that forms the foundation for the system's overall health.
 

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In 1982, they were everywhere. Thousands of mushy, globular bodies attached to tens of thousands of tiny, tubular feet, each moving slowly across the ocean floor with clear, instinctual determination. Driven by the urge to eat and defended by a dome of stubby spikes, Maine's population of green sea urchins (Strongylocentrotus droebachiensis) were the miniature versions of so many punk rock buffalo, grazing their way across the Gulf of Maine in seemingly endless, insatiable herds. Fast forward to 2002. In less than 20 years, the gulf's vast, prickly carpet of urchins was reduced by hundreds of millions of animals by overfishing, the survivors sprinkled far and wide along Maine's ragged coast. But the urchins' story is not as simple as it might seem. Like so many other organisms that have been harvested from the waters of the Northeast, the urchin is just another character in a very long and complicated story a story marked by intricate plot twists, shocking irony and a conclusion that is shaping up to be downright terrifying.
 

With more than a quarter-century on the front lines of marine research, Bob Steneck is a man who knows when to fish and when to cut bait. The University of Maine School of Marine Sciences researcher has spent his career unraveling the intricacies of the world's marine ecosystems, and his "big picture" approach to conservation and fisheries management has helped to tie the oceans' many divergent plot lines into a single, unified tale of global turmoil and anthropological excess. From searching for fish bones in 2,000-year-old trash heaps to studying Caribbean corals with the help of high-tech diving gear, Steneck has gathered considerable evidence that suggests that the coming years may be particularly critical for many marine ecosystems as they exist today.

The story is still being written, but Steneck, for one, is bent on creating a happy ending.

"I'm generally an optimist at heart, but there are some serious threats to the world's oceans," Steneck says. "We tend to look at the planet, and in particular the oceans, as this stable, permanent, nurturing source of life, but as science peels back the layers, what we see is a global ocean in trouble."

Pointing to a growing list of health threats to the world's oceans, Steneck describes a common pattern of slow, incremental overload and sudden collapse, suggesting that the Blue Planet's ability to absorb the insults of human misuse have clear limits. The notion of ecological thresholds is at the core of Steneck's assessment of the seas. As pressure on the marine environment continues to grow, these thresholds are being met and surpassed.

A classic example of the threshold phenomenon can be found in the sad tale of the green sea urchin. Prolific and plentiful across the Gulf of Maine, urchins spent decades quietly munching at the Atlantic's undersea salad bar, unaware of the socioeconomic tsunami on the horizon.

As urchin populations in other parts of the world were rapidly depleted by overfishing through the 1970s and '80s, a seemingly insatiable Asian market turned its hungry eyes toward Maine, creating a boom-and-bust fishery that crashed a multimillion urchin population in less than two decades.

Steneck used the urchin story to illustrate the effects of roving bandits in a paper he coauthored with UMaine marine scientist Jim Wilson and others, recently published in the journal Science.

"The urchin story is classic overfishing. Because of the globalization of fisheries, the Japanese were able to deplete the global stock. They could afford to pay top dollar in places like Maine, but they had no stake in the health of our local ecosystem. Harvesters who move into a fishery and deplete the resource without any kind of investment in the ecosystem's long-term health are the definition of the roving bandit," says Steneck, who is based at the Darling Marine Center in Walpole, Maine.

"The collapse of the urchin fishery was marked by a cascade of ecological and socioeconomic effects. We can see the effects of surpassing the economic thresholds in the fishery: processors and distributors pull out, harvesters go out of business, but the effects of surpassing the ecological threshold are unknown.

"We don't know the implications of targeting the Gulf of Maine's most significant herbivore. But we do know that there is more seaweed sprouting in the Gulf of Maine than there's been in decades."

The prequel to the urchin story adds yet another twist to the tale: the urchin's preharvest heyday itself was due, at least in part, to yet another case of overfishing. For millennia, the Gulf of Maine was ruled by the mighty cod. The powerful carnivore's mustached mouth gobbled untold thousands of crabs, lobsters, shrimp and, of course, urchins during its tenure as dominant predator. But cod proved to be too tasty for its own good, quickly becoming the target of an international race to capture the most fish.

Humankind's appetite for salted cod, dried cod, boiled cod and cod chowder inspired a race for more traps, bigger nets, more powerful boats and so on. The technological onslaught proved too much, putting cod and other groundfish on Maine's long list of collapsed fisheries. As the cod population dwindled, the urchin population mushroomed. And now, kelp and other algae are taking advantage of their freedom from the urchin's hungry herbivory.

With their big-brained ability to find new ways to exploit marine resources, humans have proven again and again their knack for surpassing ecological thresholds and upsetting the natural balance beneath the waves. Steneck hopes to stabilize our relationship with the sea by finding new ways to fish that work more harmoniously with natural processes.

"Following the evidence drawn from marine research over the years is like watching an episode of CSI: The science is very good at telling us what made the victim die," says Steneck. "What we are learning is that the role of consumers, or predators, in marine ecosystems is much more significant than it had been considered in the past.

"Loss of large predators from the system has a much greater impact than nutrient run-off or invasive species or any of the other factors threatening ecosystem health. One could argue it is the biggest issue facing fisheries management."

Steneck maintains that marine ecosystems are structured by their large predators, and that the lack of large predators due to overfishing can cause the populations of other organisms within the system to fluctuate uncontrollably. After nearly 400 years of intense groundfishing in the Gulf of Maine, declines in the cod population led to increases in the number of shrimp, lobster, urchins and other prey species.

While some might argue that an increase in lobsters or other species humans find tasty is a good thing, the population swings of prey species represent a system out of balance, and it is that balance that is so important to maintaining healthy ecosystems and sustainable fisheries.

Worldwide, many marine species once abundant are now rare, and dramatic increases in populations are often the precursor to disease outbreaks. In Maine, where fishermen once split their efforts between several different species throughout the year, fully 80 percent of the state's fisheries income now comes from a single species: the American lobster.

To put that into perspective, there are more than 50 other marine species that split the remaining 20 percent of Maine's commercial fisheries income. Sales of bloodworms for fish bait contribute more to the state economy than cod.

"We need to manage our fisheries in a way that will bring back the dominant predators to restore diversity. A diversified ecosystem can support diversified fisheries, and that is the only way to maintain sustainable harvests," Steneck says.

With 80 percent of Maine's fishing economy riding on lobster, a disease outbreak could devastate the state's socioeconomic fabric. That's what happened in Rhode Island, where lobster shell disease collapsed the industry. Fishermen know the danger of depending too much on one species, says Steneck, who advocates broad changes in how fisheries are managed.

"When I first began doing research and working with fishermen, there was open hostility between managers, fishermen and scientists. Just in the past five years, fishermen have gone from being in denial to openly admitting there's a problem."

Steneck hopes to reinvent fishing by changing the way we look at harvesting and management. Almost all commercial fishing has aimed at capturing the biggest individuals of the target species, leaving smaller, younger animals to replenish the stock. But to increase a fishery population, it isn't enough to increase mesh sizes or minimum lengths, Steneck contends.

As part of the natural process, predators take the bite-size and injured, often leaving the biggest, healthiest, reproductive animals. Steneck says it's important to do the same in fisheries management by preserving the largest and smallest of the species.

"If we could change our focus to target the intermediate-size animals, our fisheries would be more sustainable and the ecosystem would benefit," says Steneck.

By David Munson
September-October, 2006

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