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5 December 2013 11:26 am ,
Vol. 342 ,
At age 30, Dutch biologist Freek Vonk has built up a respectable career as a snake scientist. But in his home country,...
Since arriving on the island of Guam in the 1940s, the brown tree snake ( Boiga irregularis ) has extirpated native...
An animal rights group known as the Nonhuman Rights Project filed lawsuits in three New York courts this week in an...
Researchers have been hot on the trail of the elusive Denisovans, a type of ancient human known only by their DNA and...
Thousands of scientists in the Russian Academy of Sciences (RAS) are about to lose their jobs as a result of the...
Dyslexia, a learning disability that hinders reading, hasn't been associated with deficits in vision, hearing, or...
Exotic, elusive, and dangerous, snakes have fascinated humankind for millennia. They can be hard to find, yet their...
Researchers have sequenced and analyzed the first two snake genomes, which represent two evolutionary extremes. The...
- 5 December 2013 11:26 am , Vol. 342 , #6163
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Clams Show Colorado River Decline
12 December 2000 7:00 pm
Conservationists have long contended that dams and water diversion have destroyed the biological richness of the Colorado River delta, a key nursery of marine life that flows into the Gulf of California. Now researchers have confirmed those suspicions by counting ancient clam shells. They estimate that the river has lost about 95% of its productivity since the Hoover Dam was built in the 1930s.
Unlike soft-bodied animals that decay without a trace, clams leave behind hard shells that record their past abundance. Clams also hint at an ecosystem's health, because many fish, mammals, and migratory shorebirds depend on them for food. A team of researchers led by geoscientist Karl Flessa of the University of Arizona in Tucson hoped that analyzing ancient shells would allow them to estimate the delta's biological productivity both before and after the river's water was diverted.
First the researchers estimated how many clams lie entombed in the delta's massive shell ridges and islands. After analyzing satellite images, excavating trenches in shell-rich beaches, and making other field measurements, they came up with a grand total of some 2 trillion clams. Then they dated 125 shells and inferred that almost all of those 2 trillion shells accumulated between A.D. 950 and 1950. Finally, they calculated the population's turnover rate to estimate an average density of 50 clams per square meter over the last millennium--a number that contrasts with fieldwork earlier this year that yielded just three clams per square meter, they report in the December issue of Geology.
Paleontology studies such as this can "establish an ecosystem's long-term past before humans altered it," says invertebrate paleontologist Sally Walker of the University of Georgia, Athens. And that provides "a metric, or benchmark, for attempting remediation," Walker says.