Dragged river crab also eats land plants if necessary

Researchers conclude the secret of success of the globally successful intruder

Red American Crayfish (Procambarus clarkii) © Mike Murphy / Public Domain
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The Red American Crayfish is a true survivor: whether introduced or deliberately located somewhere, this freshwater crayfish is considered one of the most successful invasive species in the world. One of his secrets of success has now been elucidated by British researchers. If he does not find enough food in the water, the crab simply crawls to the shore at night and nibbles on grasses and other land plants there. For the first time, such behavior has been demonstrated in this ecologically important type of cancer, according to biologists in the journal PloS ONE. So far, it has been thought that crayfish seek food only in the water or in flooded paddy fields, but not along the dry shores of an African lake. But that's exactly where the scientists have caught him now.

"This shows why crayfish is such an extraordinarily successful conqueror, " says first author Jonathan Gray of Queen Mary University of London. He is extremely flexible and adaptable. With these extra rations from the land he could survive even under bad conditions better than many native aquatic animals. This shows that you have to be very careful when bringing this cancer into a new area - you will not let go of it.

The approximately hand-sized red American crayfish (Procambarus clarkii), also called Louisiana crayfish, was originally native only in the southeastern United States and along the Caribbean coast. In the meantime, however, it has been partially accidentally dumped in ponds and stagnant waters of almost all continents - partly because it is bred and kept in large quantities as the most important supplier of crab meat. This usually has dramatic ecological consequences, the researchers say. The crayfish decimates the aquatic plants, destroy the banks through its caves, change the composition of the communities and also litter the cancer. This fungal disease threatens to eradicate now in Europe, the domestic crayfish.

Examine food of the intruder in Africa

For their study, the researchers investigated red American crayfish at Lake Naivasha in Kenya. The cancer was used there in 1970 to decimate, among other things, a domestic snail species, which carries the causative agent of the tropical disease schistosomiasis. The lake is often almost dry in the summer, the scientists report. For the cancer then little food, because

Water plants and aquatic small animals are then rare. Nevertheless, the newcomer survived without any problems - but so far was not clear. display

The researchers collected crayfish from different areas of the lake for three years in July. In a very dry year they found 16 animals in deeply sunken, waterlogged footprints left by hippopotamus on the shore. In all cancers, they took tissue samples and analyzed the proportions of various carbon and nitrogen atoms therein. As these atoms are taken up with food and incorporated into the tissue, the isotope distribution dissipates what an animal has eaten.

"Among the animals we found in the hippo tracks, land plants like Kn terich and Kikuyugras accounted for 27 percent of the food, " write Gray and his colleagues. Apparently the crabs would have left their puddles at night and crawled over the dry soil to these land plants to do well. That had not been the case in moister years. The cancer adapted to adapt flexibly to climate and the environment.

(PloS ONE, 06.08.2012 - NPO)