Discovery Of The Week: Purple Philippine Freshwater Crabs
April 24, 2012

Discovery Of The Week: Purple Philippine Freshwater Crabs

The Philippines is the setting for the latest spectacular discovery: Four new species of crabs, most of which have purplish shells and live in lowland-forest ecosystems, discovered by a team of German scientists, reports National Geographic.

The four new discoveries, all of which are found only on the island of Palawan, were co-discovered and described by Hendrik Freitag of Germany´s Senckenberg Museum of Zoology.

“In the Aqua Palawana research program I am head of, we have been investigating the biodiversity of Palawan´s inland waters for over 10 years”, said Freitag. “This also included taking a closer look at the Insulamon crabs and we discovered four new species in the process.”

Freitag said the crabs, members of the genus Insulamon, burrow under boulders and roots in streams, feeding on dead plants, fruits, carrion and small animals in the water at night. He said that most of the crabs have purple shells, with red-tipped claws and legs. They are between one and two inches wide.

Freitag said the four new crab species adds to the one other known species in the genus, I. unicorn, found in 1992. The most common of the newly discovered species, I. palawanense, seems to be widespread on the island, said Freitag. The other three, however, are restricted to specific creeks. All four are freshwater crabs, but can spend fairly good amounts of time on land, thanks to their large gill pockets, he added.

Freitag and colleagues, whose study is published in the journal Raffles Bulletin of Zoology, are unsure why the animals are so brightly colored, although they suspect it may help them recognize each other. Interestingly, dominant males of the species are more reddish in color, in contrast to the purple of females and less dominant males.

“It is known that crabs can discriminate colors. Therefore, it seems likely that the coloration has a signal function for the social behavior, e.g. mating,” Freitag told AFP by email. “This could explain why large males of various Insulamon species are more reddish compared to the generally violet females and immature males.”

The crabs, as spectacular as they may be, are under constant threat from farming and development in the Philippines. These creatures need healthy bodies of freshwater to thrive and cannot live in saltwater or travel long distances over land. They are especially vulnerable to habitat loss.

Palawan is located between and combines two of the world´s most important biodiversity hotspots, Philippines and Sunda Islands. Around 50 percent of fauna and flora species living on Palawan are endemic, exclusively native to the island.

US-based Conservation International lists the Philippines as one of 17 countries that contains most of Earth´s plant and animal life.

Freitag said the main threat to Palawan´s most precious species is mining. In fact several mining projects are currently in the works despite massive protests by people from all over the world, including the indigenous peoples of the region.

But even if the habitat is not entirely uprooted, the smaller the habitats become, the greater the risk of extinction for many species, Freitag warned. That´s why it is important now to continue research in this biological hotspot and “show that the biodiversity of these islands is unique and worth protecting,” he added.

As an associate professor at the Ateneo de Manila University, Freitag increasingly gets local students involved in bio-systematic research, in order to create awareness of this unique habitat.

Participants of the Aqua Palawana program include Senckenberg and the Phyllodrom Leipzig, Ateneo de Manila University, Western Philippines University, De La Salle University Manila and the Philippine National Museum, as well as the Vienna Natural History Museum and the National University of Singapore.


Image Caption: A particularly colorful new species: Insulamon palawanense © Senckenberg