Washington, August 29 : A study on a newly discovered living species of giant clam called Tridacna costata suggests that modern humans' dispersal out of Africa into the Red Sea and adjacent regions 110,000 to 90,000 years ago might have been driven largely by competition for marine resources.
Fossil evidence reveals that the new species called Tridacna costata once accounted for more than 80 percent of giant clams in the Red Sea, while it presently represents less than one percent of giant clams living there.
Claudio Richter of the Alfred-Wegener-Institute for Polar and Marine Research in Germany says that new species appears to live only in the shallowest waters, making it particularly vulnerable to over-fishing.
"These are all strong indications that T. costata may be the earliest example of marine overexploitation," he said in a research paper published in the online edition of the journal Current Biology
Richter said that the Red Sea might have acted as a bottleneck when modern humans coasted out of Africa during the last interglacial some 125,000 years ago, and its overall aridity may have driven the early hunter-gatherers to rely on shallow-water marine resources.
He said that giant clams would have been a prime target, because of their sedentary nature, conspicuousness, and large size.
"Our discovery that T. costata was already on a trajectory of decline prior to this period corroborates this hypothesis, by providing the first circumstantial evidence that humans were not only using but also depleting reef resources, making T. costata the likely earliest victim of anthropogenic degradation of coral reefs," the researchers wrote.
"Declining marine and terrestrial resources, by human and climatic factors, respectively, may have acted in concert to thwart the precocious but short-lived colonization of the Near East by anatomically modern but technologically primitive humans at the end of the last interglacial," they added.
The research team, including scientists from the Center of Tropical Marine Ecology in Germany and the University of Jordan, discovered the new species while attempting to develop a breeding program for another prized giant clam species.
Study coauthor Hilly Roa-Quiaoit of Xavier University in the Philippines, known as the "mother of clams," recognized the new species, which can measure up to a foot long and has a shell with a distinctive zig-zag outline, as a new variety.
The new giant clam differs from others in the Red Sea in an early and brief reproductive period each spring, coinciding with the seasonal plankton bloom.
Underwater surveys carried out in the Gulf of Aqaba and northern Red Sea revealed that the long-overlooked clam must be considered critically endangered, for only six out of a thousand live specimens the researchers observed belonged to the new species.