Rare Iguanas in Galapagos Are Victims of Oil Spill

ANDREW C. REVKIN / NY Times 5jun02

It was thought to be a fortunate near miss when the grounded tanker Jessica disgorged 150,000 gallons of diesel and bunker fuel amid the biological riches of the Galapagos Islands in January 2001.

Fortuitous wind shifts sent most of the slick to sea and, as a result, deaths of sea lions and sea birds were in the dozens and the shrine to the powers of natural selection appeared largely spared.

Now, however, biologists conducting a long-term study of the islands' unique marine iguanas have found strong evidence that small amounts of oil caused a big die-off of the algae-eating lizards in the months following the spill.

Their theory, to be tested in experiments later this year, is that the oil killed bacteria in the guts of the reptiles that allow them to digest seaweed and they starved.

The iguana species — dispersed over many of the dozens of islands — is not threatened, but the research provides new evidence that small marine oil spills can potentially have far-reaching, and subtle, toxic effects, several marine biologists said.

The Galapagos discovery came indirectly from an ongoing study in which 1,300 iguanas on two small, similar islands were marked in 1987 and monitored ever since. The findings are described in a brief paper in the journal Nature, which is to be published on Thursday.

It follows the release two weeks ago of a comprehensive study by the National Academy of Sciences that emphasized the threat posed by low concentrations of oil spilled in the sea.

One of the authors of that study said the Galapagos findings, though still lacking specific evidence of the toxic effect, was compelling. "The circumstantial evidence would certainly suggest that oil exposure was a critical factor," said the author, Dr. Judith E. McDowell, a zoologist at the Woods Hole Oceanographic Institution.

Surveys of iguanas before and after the spill determined that more than 60 percent of the marked animals on Santa Fe — an island that was contaminated with about a quart of oil along each yard of its windward shore — died by the end of 2001. Many iguana skeletons were also recovered along the tide line.

No similar die-off happened on Genovesa, an uncontaminated island with a marked iguana population, about 60 miles to the north, according to the researchers.

"There's nothing else we can imagine that could kill 60 percent of a population," said Dr. Martin Wikelski, an ecologist from Princeton University who led the Galapagos study. "At the same time, we know these hindgut bacteria can be affected by oil."

The marine iguanas of the Galapagos lack any natural foes and generally die either of old age or of starvation when periodic El Nino warmings of the eastern Pacific kill off the shallow beds of seaweed they graze.

But the last El Nino warming ended in 1998 and the oil spill occurred when the Pacific was in a cool phase called La Nina. Also, the die-off after the spill killed iguanas of all sizes on Santa Fe, while the natural weather cycles tend to kill mostly large old animals that need the most seaweed.

Another hint that something in the diet contributed to the mortality on Santa Fe was a spike in the animals' blood levels of a steroid, corticosterone, that is produced when they face physiological stress.

The National Science Foundation has given the research team a grant to return to the islands toward the end of this year and run experiments to test the potential toxicity of oil to the lizards' gut bacteria, Dr. Wikelski said.

He said Ecuadorian national park officials have agreed to the tests, which would involve feeding clean and oil-tainted seaweed to captive animals.

The work on the cause of the iguana die-off is an undesired shift for Dr. Wikelski, whose main focus had been a 20-year study of the animals' behavior and population patterns. He said that study was essentially ruined because so many of the marked, closely monitored animals died.

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Oil Spill Kills Galapagos Iguanas AP 5jun02

As many as 15,000 marine iguanas died on a Galapagos island in the year after an oil spill, say scientists who blame trace amounts of the fuel.

Naturalists initially believed that the unique Galapagos ecosystem that inspired Charles Darwin's theory of evolution largely escaped damage from the January 2001 spill.

A year after a tanker ran aground off San Cristobal Island and leaked about 170,000 gallons of fuel, a report by the Charles Darwin Foundation logged just six animal deaths attributable to the spill.

But now, Martin Wikelski, part of a team that has spent 20 years studying a species of iguana unique to the Ecuadorean islands, said the spill had a far larger impact.

Writing in Thursday's issue of the journal Nature, the Princeton University ecologist and his co-authors estimate as many as 15,000 marine iguanas died on Santa Fe Island in the 11 months after the accident. In one iguana colony on the island, 30 miles west of the spill, 62 percent of the animals previously marked by researchers perished.

``We came back after a year and were astonished to find a large number of skeletons on the coast,'' Wikelski said.

In contrast, a marine iguana population on Genovesa, an island 75 miles to the north that was untouched by the spill, remained stable with no deaths among the marked reptiles there.

Wikelski said the iguanas are territorial and tend to stay put, allowing scientists to count them accurately.

He said there is little risk of any long-term effect on the marine iguanas, since they are accustomed to having their numbers decimated by food shortages.

Wikelski said he is uncertain why the Santa Fe iguanas died but suspects oil is the culprit. Although relatively small amounts of oil washed ashore on Santa Fe, he believes it was enough to disrupt the intestinal bacteria that the ocean-diving creatures rely on to digest the algae they eat.

Wilkelski and the Galapagos National Park are suing Petroecuador, Ecuador's state-owned oil company, for $600,000 in damages. Petroecuador President Rodolfo Barniol would not comment on the study or the lawsuit.