Study: Ancient excesses tangled sea's food web

DEPLETION: Modern Earth feels effects of overfishing, overhunting by early humans.

By Paul Recer
The Associated Press

Washington — Ancient humans started destroying the abundance of the seas by slaughtering whole species, changing a delicate balance that was tipped further by excesses of the modern age, a study finds.

A cascade of environmental damage that changed the pristine Earth was started thousands of years ago by the destruction of key species, such as sea turtles in the Caribbean, sea cows off the coast of Australia and sea otters near Alaska, researchers say in a study appearing today in the journal Science. The effects of that damage continue.

"There's been a longtime belief that everything was fine until the . . . Europeans showed up," said Karen Bjorndal, a zoology professor at the University of Florida. "Now we've discovered that the start of the environmental problems (in the sea) go way back before that."

"The notion of the native peoples having a benign impact on the environment in their vicinity has been challenged," said Charles Peterson, a professor of marine sciences at the University of North Carolina at Chapel Hill. "The general feeling is that there were dramatic effects locally and not a prudent predation" by ancient humans long before the colonial and industrial eras.

Based on the combined research of 19 scientists on four continents, the study shows that careless and excessive harvesting of food from the sea as early as 10,000 years ago caused changes in the ecosystems and made the environment more easily damaged by the wholesale exploitation of modern man.

James Acheson, a marine scientist at the University of Maine, called the research "a breath of fresh air" in the understanding of marine ecology and how it has been affected by humans.

"They are pointing toward a new way to look at the oceans," Acheson said. "They show that human predation preceded all the other damage" done to the oceans.

In the study, researchers analyzed the effect that the loss of species has had on the intricate food web of coastal areas in the Americas, Australia and Europe. Included were an analysis of kitchen debris left by ancient humans; reports on the abundance of sea life by explorers in the 18th and 19th centuries; and modern wildlife population studies.

"It is astonishing the effect we have had on the Earth," Peterson said.

Bjorndal said algae now choking and killing many coral reefs in the Caribbean can be traced to the slaughter more than 3,000 years ago of the green sea turtle and to other animals that grazed on the plant.

She said a study of kitchen refuse piles from the Amerindian peoples who first settled the Caribbean showed that they depended heavily on the sea turtle for food. The animals were easy to catch as they regularly lumbered ashore to lay eggs on the semitropical islands.

But evidence of turtle slaughter in the kitchen refuse grew less and less with the passage of time until, finally, "the turtles disappear entirely. It is clear the nesting colonies were wiped out," Bjorndal said.

With the turtle gone, the people turned to other food, such as the large parrot fish, a meaty dweller of the reef. It too eventually became scarce, as did other plant-eating animals.

"We reduced the system to one plant-eating species," a type of sea urchin, Bjorndal said. "The system continued to function, but it was incredibly vulnerable."

That was shown when, starting 15 years ago, disease wiped out the sea urchin, she said. Algae quickly exploded in growth, smothering many coral reefs. That doomed many species in the reef.

"This was a process that was set in motion when the (native people) killed off the sea turtle," Bjorndal said.

Another example cited by the researchers is the loss of vast kelp forests that once grew thickly offshore along North America's east and west coasts.

Overharvesting of the sea otter, starting 2,500 years ago, led to a huge population of sea urchins, the otter's principal food. The sea urchins grazed away the kelp forests, causing a steep decline in fish populations.

In modern times, the sea otter has been protected from human hunters, but now, because of mankind, it has a new enemy: the killer whale.

Peterson said the killer whale normally dines on seals. The population of seals has fallen dramatically over the past 200 years, however, because of fur hunters and later because of overfishing by humans that deprived the seals of food. Since there are few seals to feed on, the killer whale now preys on the sea otter. This allows the sea urchin to graze down the kelp forest.

Bjorndal and her co-authors believe some of the environmental loss can be recovered with new programs to protect sea life and control fishing.

Many of the depleted animals are not extinct and could be brought back to restore a lost balance, she said.

"One of our main messages is that there is hope," she said.

I don't think people realize how the ocean has changed historically," Gaines said. "If you contrast what's out there now to what was there 200 years ago, it's just crumbs.

THE WORLD

Overhunting Has Ravaged Sea Habitats, Study Finds

Ecology: Long-term damage to kelp forests and coral reefs has upset nature's balance and decimated marine life, report says.

By KENNETH R. WEISS, TIMES STAFF WRITER

Centuries of excessive hunting on the high seas, besides devastating the populations of whales, sea turtles, sea cows and otters, has set in motion the collapse of kelp forests, coral reefs and other marine habitat essential for sea life, scientists reported today in the journal Science.

A team of 19 scientists from around the globe has concluded that overfishing and overhunting have had far worse effects on coastal marine habitat than pollution or global warming.

For example, California's coastline was thick with fish and kelp forests until urchins, unchecked by otters and predators that had been hunted out, started a destructive pattern of grazing that reduced the coastline to barren rocks and sand. "A kelp forest is the equivalent of a forest of trees on land. If it disappears because of an imbalance of predators and herbivores, then the whole system crashes," said lead author Jeremy Jackson, a marine biologist at Scripps Institution of Oceanography in La Jolla.

Citing historical accounts of marine life abundance, the report says that recent assessments of losses don't go back far enough to convey a true sense of the enormous decline.

"We all know that the oceans are overfished and there used to be a lot more out there," Jackson said. "But when we started looking into historical records, it exceeded all of our imaginations."

Jane Lubchenco, a marine ecologist at Oregon State University, said she found the report very startling. "It provides the first credible analysis of the magnitude of human impacts on the ocean."

Poring over records of sediment from the ocean floor, archeological digs and historical harvests, the scientists rediscovered oceans so teeming with whales, sea turtles and fish that they seem akin to a world fantasized by Jules Verne.

In the Caribbean, for instance, sea turtles so crowded the bays that Christopher Columbus worried that his ship would run aground on them when he discovered the New World.

Millions of green turtles used to closely crop turtlegrass. Now that the turtles are largely gone, the turtlegrass in Florida Bay is being consumed by a fungus that depletes oxygen needed by fish to survive.

In Chesapeake Bay, oyster beds once were so thick they posed navigational hazards. The mollusks also filtered the bay water so quickly that the Chesapeake was crystal clear rather than its current murky green.

Since the over-harvesting of oysters, the altered water chemistry has made the Chesapeake inhospitable to the once abundant populations of manatees, giant sturgeon, whales and alligators, according to the report.

Along the Pacific Coast and the Aleutian Islands, sea otters once kept sea urchins in check with their insatiable appetite for the spiny creatures.

Beginning with the native Aleuts and finishing with 19th century fur traders, the otters were hunted to the brink of extinction.

That allowed the urchins to munch their way through the kelp forests—a phenomenon that spread later to Southern California after other urchin predators, the lobster and sheepshead fish, had been overfished, said Jim Estes, a marine ecologist with the U.S. Geological Survey.

Such a change has sharply diminished the kelp forests that provide food, shelter and breeding grounds to so many creatures.

"What amazed me is the same thing has happened in the Gulf of Maine," Estes said. The Atlantic cod were important predators of urchins, he said, until they were nearly wiped out by overfishing. In their absence, exploding urchin populations laid waste to sea vegetation.

In case after case, the scientists and historians found that once one strand in the food web was removed by overfishing, the entire ecological system began to unravel.

Removal of key predators or other animals has set off sequences of events that are now culminating in blooms of toxic algae, ocean dead zones, outbreaks of disease and other symptoms of ecological instability.

Steve Gaines, director of the Marine Science Institute at UC Santa Barbara, believes that the scientists have pointed out a fundamental flaw in government attempts to manage fishing industries.

State and federal regulators impose catch limits, or quotas, that often are based on estimates of how many of a certain species would be in the ocean—if not subjected to fishing pressure. But such estimates reflect relatively recent populations that were already substantially reduced, suggesting that quotas merely tinker with tiny, remnant populations.

"I don't think people realize how the ocean has changed historically," Gaines said. "If you contrast what's out there now to what was there 200 years ago, it's just crumbs."

Gaines is part of a group of California biologists designing a network of marine reserves along the state's coastline—areas to be off limits to fishing—to give species a chance to recover.

Jackson said such efforts are laudable. But he believes that they have little chance of restoring what once existed in the ocean, without extensive human effort to re-create through captive breeding programs what has been lost.

On a bright note, the article maintains that there have been very few documented cases of outright extinction of marine species. So most creatures still exist somewhere in the ocean. That comforting information, however, does not give the scientists cause for complacency.

"We need to intervene and need to intervene in a massive scale," Jackson said. "But we have a problem. We do not have viable science on how to put Humpty Dumpty back together again."

Copyright 2001 Los Angeles Times

Re "Overhunting Has Ravaged Sea Habitats, Study Finds," July 27: In hundreds of years of colonizing America, have we so forgotten what this country was like before? Where once passenger pigeons darkened the sky for an entire day as they flew over the land. Where buffalo numbered in the millions. Where the Eastern forests had hickory trees and maples that were as big around as a room, and you could sink down into the mulch up to your waist, and there was more life in one square acre than you can imagine now. Is the reality of what it was like completely lost to any memory alive today?

What about the fisheries of the West Coast? We have photos from the turn of the century of people pulling 75-plus-pound tuna out of the waters off Catalina all day long. Where are those fish now? If you look at a photo from space of the world, what you see is shocking. It suggests that we are the mange on the dog. And we are killing this dog that supports us. Overpopulation is the big issue. But this won't be addressed by the Bush administration. Its agenda seems to be the economic interests of corporate structures. More people equals more consumers. Human egotism will make excuses for why we're destroying the planet. Wake up, folks.