New species of giant clam discovered in the Red Sea

31/08/2008 21:29:47 August 2008. A new species of giant clam in two decades, previously only known from fossil records, has been discovered in the Red Sea. While fossil evidence reveals that the new species, named Tridacna costata, once accounted for more than 80 percent of giant clams in the Red Sea, it now represents less than one percent of giant clams living there.

The new species appears to live only in the shallowest waters, making it particularly vulnerable to many centuries of overfishing by humans. Modern humans are believed to have coasted out of Africa during the last interglacial period, some 125,000 years ago. The Red Sea, a saltwater inlet between Africa and Asia, may have acted as a bottleneck, and its overall aridity may have driven the early hunter-gatherers to rely on shallow-water marine resources. Giant clams would have been a prime target, because of their sedentary nature, conspicuousness, and large size.

"These are all strong indications that T. costata may be the earliest example of marine overexploitation," said Claudio Richter of the Alfred-Wegener-Institute for Polar and Marine Research in Germany.

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, they report. Underwater surveys carried out in the Gulf of Aqaba and northern Red Sea revealed that the long-overlooked clam must be considered critically endangered. Only six out of a thousand live specimens the researchers observed belonged to the new species.

Overfished for 100,000 years
Early shell fishing evidence in other areas has led to speculation that the dispersal of modern humans out of Africa into the Red Sea and adjacent regions 110,000 to 90,000 years ago was driven largely by competition for marine resources, the researchers said.

"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," they 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."

The research team, including scientists from the Centre 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 co-author 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.

Analysis of those apparent differences in morphology confirmed that the species was in fact clearly distinct. To further resolve the relationship of this new variety to the other giant clams, Marc Kochzius at the University of Bremen led the molecular genetic analysis, which confirmed T. costata as a new species.