These giant clams called Tridacna costata are two feet long and may have sustained prehistoric humans as they first migrated out of Africa.There are strong indications that T. costata may be the earliest example of marine overexploitation.
New Giant Clam Species Offers Window Into Human Past
ScienceDaily 28 Aug 08;
Researchers report the discovery of the first new living species of giant clam in two decades, according to a report to be published online on August 28th in Current Biology. While fossil evidence reveals that the new species, called 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 researchers said they cannot say for sure which factors contributed to the loss of this giant clam species in favor of others, but the overall decline in giant clam stocks and the striking loss of large specimens is a "smoking gun" for overharvesting by humans many thousands of years ago, said Claudio Richter of the Alfred-Wegener-Institute for Polar and Marine Research in Germany. The new species appears to live only in the shallowest waters, making it particularly vulnerable to overfishing.
"These are all strong indications that T. costata may be the earliest example of marine overexploitation," he said.
Modern humans are believed to have coasted out of Africa during the last interglacial, some 125,000 years ago, Richter said. 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, he 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.
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.
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.
Early shellfishing 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 researchers include Claudio Richter, Alfred-Wegener-Institute for Polar and Marine Research, Bremerhaven, Germany; Hilly Roa-Quiaoit, Xavier University, Cagayan de Oro, Philippines; Carin Jantzen, Center for Tropical Marine Ecology, Bremen, Germany; Mohammad Al-Zibdah, The University of Jordan, Yarmouk University, Aqaba, Jordan; and Marc Kochzius, University of Bremen, Bremen, Germany.
Giant Clams Fed Early Humans
Charles Q. Choi, LiveScience.com Yahoo News 28 Aug 08;
Giant clams two feet long might have helped feed prehistoric humans as they first migrated out of Africa, new research reveals.
The species, Tridacna costata, once accounted for more than 80 percent of giant clams in the Red Sea, researcher now say. Today, these mollusks, the first new living species of giant clam found in two decades, represent less than 1 percent of giant clams living there.
This novel clam, whose shell has a distinctive scalloped edge, was discovered while scientists were attempting to develop a breeding program for another giant clam species, Tridacna maxima, which is prized in the aquarium trade. The new species appears to live only in the shallowest waters, which makes it particularly vulnerable to overfishing.
"These are all strong indications that T. costata may be the earliest example of marine overexploitation," said researcher Claudio Richter, a marine ecologist at the Alfred-Wegener-Institute for Polar and Marine Research in Bremerhaven, Germany.
Fossil evidence that the researchers uncovered suggests the stocks of these giant clams began crashing some 125,000 years ago, during the last interval between glacial periods. During that time, scientists think modern humans first emerged out of Africa, Richter said.
These mollusks could have played a key role in feeding people during that crucial era, serving as a prime target due to their large size, the scientists added. Indeed, competition for these clams and other valuable sea resources "may have been an important driver for human expansion," Richter told LiveScience.
Since this new species bore some features in common with two other living species of Red Sea clams, at first the researchers thought the new mollusk might have been a hybrid, but genetic analysis showed otherwise. These results were further corroborated by marked differences in behavior - while the other two clams spawn over a long period in summer, the new species reproduces during a brief spurt in spring.
No one had expected to discover a new giant clam species, "particularly in the Red Sea, one of the best investigated coral reef provinces," Richter said. The fact that it was overlooked for so long "is a testimony as to how little we really know about marine biodiversity."
Underwater surveys carried out in the Gulf of Aqaba (north of the Red Sea, between the Sinai Peninsula and Arabian mainland) and northern Red Sea revealed this long-overlooked clam must be considered critically endangered. Only six out of 1,000 live specimens the scientists observed belonged to the new species. This mollusk could be the earliest victim of human degradation of coral reefs in this region, the researchers added.
The scientists detailed their findings online on Aug. 28 in the journal Current Biology.
New Giant Clam Found; May Have Fed Early Humans
Kimberly Johnson, National Geographic News 29 Aug 08;
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.
Overeating
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."
