CHARLES DARWIN FOUNDATION PRESS RELEASE
Research on Galapagos Marine Iguanas
In a paper published today by the scientific journal Nature (volume 417, page 607, 6 June 2002) Martin Wikelski, Vanessa Wong, Brett Chevalier, Niel Rattenborg, and Howard L. Snell describe high mortality of Galapagos marine iguanas on Isla Santa Fe as a result of subtle long-term effects of the 2001 oil spill from the grounded tanker Jessica. By comparing mortality between Isla Santa Fe, an island that received relatively high amounts of oil, to mortality on Isla Genovesa, an island that received no oil, the authors confirmed that mortality due to the oil might have reached 62% of the Santa Fe population. Over the same 11 months (February through December) the mortality on Isla Genovesa was statistically indistinguishable from zero (all of the marked iguanas studied on Genovesa survived).
The authors identified four possible consequences of the oil that may have caused the high mortality:
- The oil may have had direct detrimental effects on the iguanas.
- The oil may have decreased the availability of their food.
- Fouling by the oil may have made the algae normally consumed by the iguanas unpalatable, causing starvation (marine iguanas can't readily switch to other types of food).
- The micro-organisms that live in the digestive tracts of iguanas and help the iguanas digest plant material may have been harmed by the oil.
This level of mortality is comparable to what can occur as a result of a severe El Niņo event. Marine populations have recovered from such massive die-offs when they occur naturally, but this unnatural mortality caused by the oil spill certainly makes the Santa Fe population susceptible to any further decreases in survival. If a severe El Niņo followed the oil spill, for example, the population may not be able to recover.
Dr. Howard Snell, Head of the Vertebrate and Ecological Monitoring Area of the Charles Darwin Foundation states that "Our first impression was that the biological diversity of the Galapagos had largely escaped harm from the Jessica spill. In general that is true, but the work with Martin Wikelski and his other colleagues has confirmed subtle effects that take a long time to develop and can have serious impacts for components of the Galapagos fauna."
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