The world's only uniquely tropical crayfish genus (Astacoides) is endemic to Madagascar. Its origins have long interested biogeographers as there are no native crayfish on the African mainland or the Indian subcontinent. The crayfish are a fascinating element of Madagascar's freshwater biodiversity but are also an important source of protein and income to the rural people living throughout its range (See my publications for more information on Astacoides.)
Invasive crayfish are a major threat to freshwater ecology and native crayfish populations in many parts of the world. Unfortunately, an exotic crayfish species Procambarus 'Marmorkrebs' was identified in Madagascar in March 2007. Although so far found only around the capital, it is spreading fast.
The spread of Procambarus in Madagascar is a major cause for concern as it poses a threat both to Madagascar's unique freshwater biodiversity but it also may threatened food security and livelihoods through damaging inland fisheries and rice production. I am working with colleagues at the University of Antananarivo (Jeanne Rasamy and Olga Ravoahangimalala) and Andrew Harvey carrying out preliminary research on the rate of spread and the level of risk to biodiversity and agriculture.
Read about this in The Economist (note that the article unfairly gives me credit for discovering the species in Madagascar-it was in fact first identified by Dr Jeanne Rasamy of the University of Antananarivo and Professor Kawai Tadashi of Hokkaido Fisheries Experimental Station working independently).