May 17, 2011

Hawaiian Crab Extinction Linked To Ancient Human Presence

Scientists found that the first human colonists in Hawaii wiped out land crabs that were unique to the area about 1,000 years ago.

Fossils have been found at altitudes of 3,000-feet, which is unusual for a crab.

The researchers say they identified the species by comparing it with living relatives on other Pacific islands.

They wrote in the journal PLoS One that early settlers brought in animals like pigs and rats, which helped wipe out the crabs.

The researchers describe this as the first documented extinction of a crab in the human era.

"They'd already vanished from the islands by the time the Europeans got there - nobody's ever seen one alive," said Gustav Paulay, curator of the Florida Museum of Natural History in Gainesville.

"There are stratigraphic sequences (layers of rock) that have been studied mostly for bird extinctions, and we can date when Polynesian settlers came in, partly by occurrence of Polynesian rats: and when that happens, you don't see any more crabs," he told BBC News.

Land crabs are vulnerable to contact with animals associated with human spread, and there are documented cases on islands in other places where they fared very badly when rats were introduced.

Settlement of the Hawaiian islands brought huge changes to the ecology, with many native species like birds and amphibians becoming extinct.

The researchers say the same fate came upon this land crab, which they have named Geographsus severnsi.

"When you look at the islands of the Pacific, things don't get there easily, so land animals are scarce - and the biggest things on some of them are crabs," Paulay told BBC.

"They control the ecosystems on atolls to an incredible extent."

"This particular species would have been important as a predator and as an omnivore - it would probably have had a big impact on the insect population, on land snails, and also maybe on nesting birds."

The fossils have been unearthed for many years around the Hawaiian islands, including caves in high altitudes.  Many crabs cannot live in these conditions, as they need regular immersion in salt water.

"A study like this can reveal what the structure of the natural ecosystem was before these human-caused ecological changes, and that's very important for moving forward with conservation," Helen James, curator of birds at the Smithsonian Institution's National Museum of Natural History, said in a statement..

"It highlights the complexity of the ecological changes that took place on the Hawaiian Islands and their severity in causing the extinction of a land crab."


Image Caption: University of Florida researcher Gustav Paulay examines a fossil claw of the newly described land crab species Geograpsus severnsi found on the Hawaiian Island of Kauai. Paulay, malacology curator at the Florida Museum of Natural History on the UF campus, is lead author of a study published in PLoS ONE May 16, 2011, showing the species disappeared from Hawaii soon after Polynesians colonized the islands about 1,000 years ago. Credit: Jeff Gage/Florida Museum of Natural History


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