excellent study + intro

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Posted by Lilly from ? ( on Thursday, June 06, 2002 at 12:49PM :

I just stumbled across this news article & brief scientific report in Nature. It's one of the few (if only) studies that shows the extent of environmental damage done to a given species, even by trace amounts of pollution.

"Ecologist sues over wrecked iguana study"
from Nature 417, 578 (June 6, 2002)

[LONDON] An ecologist whose studies of marine iguanas in the Galapagos Islands were damaged by an oil spill is suing the oil tanker's owner and insurer.

Martin Wikelski of Princeton University in New Jersey is seeking US$600,000 in damages as part of a wider, $14-million claim being made by the Galapagos National Park against the master, owners and insurers of the Jessica, a tanker that ran aground on the island of San Cristóbal in January 2001. The park is also suing Petrocomercial, an arm of the Ecuadorian state oil company, which owned the oil.

Wikelski has been studying the Galapagos' marine iguanas since 1987. His work has revealed, for example, how the animals' bodies shrink in response to El Niño events (see Nature 403, 37–38; 2000). But after the oil spill, the focus of his observations switched sharply from evolution to pollution.

Following the accident, Wikelski and his colleagues monitored the iguanas at an oil-affected site and at one that had escaped contamination. In this week's Nature, they report that by December 2001 more than 60% of the marked iguanas at the contaminated site had died, compared with none at the site that escaped pollution (Nature 417, 607–608; 2002).

The team suggests that small amounts of oil killed microbes in the iguanas' guts that enable the animals to digest algae, causing them to starve. "Even a tiny amount of oil in the water can be very harmful," says Wikelski.

The spill terminated Wikelski's earlier experiments, and the $600,000 represents some of the funding that Wikelski and his team had received for them from Germany's Max Planck Society, the University of Princeton and the US National Science Foundation.

The rest of the $14-million claim covers the cost of cleaning up the spill and monitoring its effects, loss of tourism and fishing revenue, and damage to the Galapagos' pristine image. "We're still feeling the economic effects," says park biologist Mauricio Velasquez.

The case was filed with the High Court at Guayaquil, Ecuador, where hearings began this February. Terra Nova, the London-based insurer of the Jessica, is contesting the right of the Ecuadorian courts to hear it. The insurer also says that the Jessica was uninsured when it ran aground because the ship's owners had not paid their premiums and had not complied with the terms of their policy. "We're just not involved at all," says Andrew Barker, an underwriter with the company. Petrocomercial declined to comment on the case.

But Ider Valverde, the leader of the park's legal team, says that the insurer is liable because it failed to notify the authorities that the Jessica was no longer covered, as is required by Ecuadorian law.

"We have made it very clear that the park is a non-profit organization, and have tried several times to settle with the insurers in an amicable fashion," says Valverde. "I imagined that they would have preferred a nice quiet settlement, but they have decided to litigate instead." If he wins, Wikelski says that any damages will be used to set up a fund to support young Ecuadorian scientists.

Nature 417, 607 - 608 (2002)
"Galapagos Islands: Marine iguanas die from trace oil pollution"

A near-miss ecological disaster still left a sinister aftermath for these giant lizards.

An oil tanker ran aground on the Galapagos island of San Cristóbal on 17 January 2001, spilling roughly three million litres of diesel and bunker oil. The slick started to spread westwards (1) and was dispersed by strong currents, so only a few marine animals were killed immediately as a result. Here we draw on long-term data sets gathered before the spill to show that a population of marine iguanas (Amblyrhynchus cristatus) on Santa Fe island suffered a massive 62% mortality in the year after the accident, due to a small amount of residual oil contamination in the sea. Another population on the more remote island of Genovesa was unaffected.

Environmental disasters such as oil fouling kill many organisms each year, but the subtle effects of low-level environmental contamination are rarely investigated (2). Although generally heralded as an ecological catastrophe narrowly averted (3) at the Galapagos World Heritage site (Fig. 1), some oil still persisted around Santa Fe (Fig. 2a), where originally about 1 litre of bunker oil came ashore per metre of beach; maximal oil concentrations reached 44 parts per million, which is low by international standards (L. Loughheed, G. Edgar and H.L.S., unpublished results).

Figure 1 The tanker Jessica ran aground in the Galapagos archipelago in January 2001.
Figure 2 Effect on marine iguanas (Amblyrhynchus cristatus) of low-level oil contamination.

The investigation of animal populations affected by environmental contamination generally begins in the aftermath of a spill so that the recovery process can be studied — as, for example, in the intertidal communities in Alaska after the Exxon Valdez accident (4). However, in the years before the Galapagos oil spill, we had accrued long-term data sets on two island populations of marine iguanas (5). We were therefore able to assess the effects of residual low-level oil contamination after the accident on one of these populations by comparing it with the other, whose habitat was unaffected.

We also compared circulating levels of the 'stress' hormone corticosterone in blood samples taken from marine iguanas on Santa Fe immediately before and shortly after the oil spill (1). We previously argued that exposed animals might suffer high mortality (Fig. 2b) as a result of the increased stress they experienced after the spill (6).

Marine iguanas are herbivorous lizards that are endemic to the Galapagos and feed solely on algae in the intertidal or subtidal zone (7). Their hindguts harbour specialized fermentation bacteria that break down algal cell walls to facilitate digestion (8). Adult iguanas are essentially free of predators on both islands, so death is normally caused by senescence or by food shortages, which affect both populations to similar extents (5). Mark-and-recapture data indicate that there were large population declines during the post-El Niño periods of 1983, 1988, 1992 and 1998 as a result of food shortages (Fig. 2c). These declines were followed by population recoveries during subsequent cold La Niña periods.

Because marine iguanas show strong site fidelity, their mortality can be measured by taking repeated censuses of study colonies (5, 6). We collected this information from the two populations over periods of 20 years (Santa Fe, 90° 02' W, 0° 50' S) and 10 years (Genovesa island, 89° 59' W, 0° 19' N), respectively, before the oil spill, and for 11 months after the oil spill (until December 2001).

Despite the reportedly low degree of oil contamination, several lines of evidence indicate that the pronounced increase in mortality that we observed among the Santa Fe animals was related to the oil spill. First, although food conditions were good, we found an unexpectedly large number of skeletons along the shores of Santa Fe; no skeletons were found on Genovesa. Second, overall iguana numbers in the Santa Fe study colony declined sharply (Fig. 2c). Third, we saw a significant reduction in the number of permanently marked iguanas on Santa Fe (Fig. 2d), whereas those on Genovesa all survived (62% local mortality of marked Santa Fe individuals; 2-test, P < 0.001).

There are four possible explanations for this high mortality in the aftermath of the oil spill. The oil may have had a direct toxic effect either on the iguanas themselves (9) or on the algae they consume (4); the animals may have declined to eat because their food had been fouled; or their vital hindgut microsymbionts may have been poisoned so that the iguanas could no longer digest their food (10).

As no deaths occurred immediately after the spill, and algal pastures and foraging were both normal in the 2 weeks after it, we infer that the fermenting endosymbionts in the iguanas' hindgut must be very sensitive to low-level environmental disturbance or contamination. This sensitivity probably compromises the digestive efficiency of affected iguanas (7), causing their corticosterone concentrations to rise (1) and triggering an increase in mortality.

Our results illustrate the severe effects that low-level environmental contamination can have on wild animal populations11. In this context, corticosterone levels are a reliable indicator of the induction of life-threatening stress (6, 11), which correlates with the ensuing mass mortality on Santa Fe (1, 6). Our findings warn against complacency over apparently low-impact contamination after environmental disasters in other wildlife areas, such as the Arctic National Wildlife Refuge in Alaska.

* Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey 08544, USA
&#8224; Department of Psychiatry, University of Wisconsin Medical School, Madison, Wisconsin 53719, USA
&#8225; Charles Darwin Research Station, Galapagos, Ecuador, and Department of Biology, University of New Mexico, Albuquerque, New Mexico 87131, USA

e-mail: wikelski@princeton.edu

References 1. Wikelski, M., Romero, L. M. & Snell, H. L. Science 292, 437-438 (2001). | PubMed | ISI |
2. Paine, R. T. et al. Annu. Rev. Ecol. Syst. 27, 197-235 (1996). | ISI |
3. Sea Technol. 42, 74 (2001).
4. van Tamelen, P. G., Stekoll, M. S. & Deysher, L. Mar. Ecol. Prog. Ser. 160, 265-277 (1997). | ISI |
5. Wikelski, M. & Trillmich, F. Evolution 51, 922-936 (1997). | ISI |
6. Romero, L. M. & Wikelski, M. Proc. Natl Acad. Sci. USA 98, 7366-7370 (2001). | PubMed | ISI |
7. Wikelski, M., Gall, B. & Trillmich, F. Oecologia 94, 373-379 (1993). | ISI |
8. Mackie, R. I., Rycyk, M., Ruemmler, R. L., Aminov, R. I. & Wikelski, M. Phys. Biochem. Zool. (submitted).
9. Prichard, A. K., Roby, D. D., Bowyer, R. T. & Duffy, L. K. Chemosphere 35, 1531-1548 (1997). | Article | ISI |
10. Ormseth, O. A. & Ben-David, A. J. Comp. Physiol. B 170, 419-428 (2000). | PubMed | ISI |
11. Fowler, G. S., Wingfield J. C. & Boersma, D. P. Auk 112, 382-389 (1995). | ISI |

-- Lilly
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