Oil Strikes Again

A second look at an oil spill once considered minor reveals that even trace amounts of environmental contaminants can have severe impacts on wildlife.

In January 2001, an Ecuadorian oil tanker ran aground near the Galápagos Islands, spilling about 150,000 gallons of oil and fuel into the biologically rich waters. The world looked on with horror. The islands, famous for their giant marine iguanas, blue-footed boobies, and Darwin's finches, seemed doomed. But strong ocean currents quickly dispersed the toxic slick, which claimed few animal casualties, and the incident was chalked up as a close call. Now, a group of researchers report in the June 6 issue of Nature that the relatively small spill had lingering, devastating effects.

Martin Wikelski from Princeton University and colleagues have spent the last 20 years studying iguana population dynamics on Santa Fe Island, where low levels of oil from the January wreck washed ashore. In the year following the spill, about 15,000 iguanas, or a dramatic 62 percent of the population, died despite normal food conditions. The researchers suspect that the iguanas, which normally die from old age or food shortages caused by natural events such as El Niño, probably starved to death.

Marine iguanas feed exclusively on nearshore seaweed, and harbor special bacteria in their guts to help digest the algae. Oil may have killed the bacteria, making it impossible for the iguanas to absorb nutrients from their food. The team will conduct experiments on island iguanas later this year to test their suspicions.

Galapagos islands affected by the oil spill.
Map by Colleen Sudukem

Iguanas on San Cristobal Island with the wrecked Jessica in the background. Photo credit: Heidi Snell

These large animals died during the oil spill, and their skulls were found afterwards along the beach in Santa Fe. As many animals died as during the last strong El Nino, but the oil spill killed many small animals as well. Photo credit: Martin Wikelsi
Martin Wikelski and co-author Vanessa Wong measuring an iguana."
Photo credit: Martin Wikelski