Genetic analysis has helped identify a new giant clam species in the Red Sea, a new study says.
The mollusk may hold clues to how and why humans migrated out of Africa more than a hundred thousand years ago.
The apparent near collapse of the species around that time likely points to overharvesting by early hunter-gatherers, says the study, published this week in the journal Current Biology.
Living specimens of the shallow-water species today are scarce. Researchers have located only 13 along the Jordanian Rea Sea coast, though the species appears to have been the dominant giant clam in ancient times.
The findings feed speculation that modern humans migrating out of Africa into the Red Sea region 110,000 years ago were motivated in part by disappearing seafood—perhaps the earliest example of marine overharvesting—the study said.
The discovery also illustrates humans' ancient dependence on the natural environment, said the study's lead author, Claudio Richter, a marine ecologist at the Alfred-Wegener Institute for Polar and Marine Research in Germany.
A New Breed
An international team of researchers discovered the new species while studying the life cycles of giant clams in the Red Sea in order to breed them for the aquarium trade, Richter said in an email.
Fossils indicate that the mysterious giant clam once dominated elevated reef terraces and began to be overharvested as early as 125,000 years ago.
While the new species accounts for more than 80 percent of the fossil shells found, it accounts for less than one percent of the current clam population, the study said.
"The further we got back in time, the more T. costata we found. Also the shells were much larger than at present," Richter said.
The new giant clam is found exclusively in very shallow waters within the easy reach of humans, which makes it much more vulnerable to overfishing than the other species, Richter said.
"The striking loss of large specimens is a smoking gun indicating overharvesting," Richter said.
That theory tracks with history, said team member Marc Kochzius, who conducted genetic analysis on the new species.
"The decline of T. costata coincided with the human coasting out of Africa," he said.
"We propose that giant clams, and especially Tridacna costata, were a valuable food resource, which was rather easy to collect on the shallow reef flat," he said in an email.
John Shea, a paleoanthropologist at New York's Stony Brook University, said the findings mesh with the hypothesis that humans began to migrate out of northeastern Africa because they were working harder for diminishing food returns.
Other factors could also have contributed to the clam species' decline, said Shea, who was not involved in the study.
"The previous decline occurred during the last interglacial period, a period of rapid climate change," where there were warmer temperatures and rising sea levels, he said in an email.
The salinity of the Red Sea could have also been a factor, he said. "It shouldn't take much change in sea chemistry to evoke major biotic changes."
for National Geographic News
August 29, 2008
source: National Geographic News