WASHINGTON — Humans started destroying the natural abundance of the seas thousands of years ago and tipped a delicate balance that left the environment more vulnerable to the excesses of the modern age, a study shows.
By widespread slaughter of sea turtles in the Caribbean, or sea cows off the coast of Australia, or sea otters near Alaska, ancient humans started a damaging cascade that changed the Earth, researchers say in a study appearing Friday in the journal Science. It still is being felt.
"There's been a longtime belief that everything was fine until the . . . Europeans showed up," said Karen Bjordal, 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 of having a benign impact on the environment in their vicinity has been challenged," said Charles Peterson of 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 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," said Acheson. "They show that human predation preceded all the other damage" done to the oceans.
In the study, researchers analyze the effect that the loss of species has had on the intricate food web of coastal areas in the Americas, Australia and Europe. Included was 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," said Peterson.
Bjorndal said algae now 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 other animals that grazed on the sea 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.
Bjorndal said an analysis of the kitchen refuse piles at ancient island village sites shows that at first "a large amount of the meat the people lived on was sea turtle."
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," she said.
With the turtle gone, the people turned to other food, such as the large parrot fish, a meaty dweller of the reef. Those, too, eventually became scarce, as did other plant-eating animals.
"We reduced the system to one plant-eating species," a type of sea urchin, said Bjorndal. "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. This in turn, doomed many species that lived in the reef.
"This was a process 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 some 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 last 200 years, however, both because of fur hunters and later 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 in turn allows the sea urchin to graze down the kelp forest.
Bjordal 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.
On the Net: Science magazine: www.eurekalert.org