Status and conservation of the giant European freshwater pearl mussel (Margaritifera auricularia) (Spengler, 1793) (Bivalvia: Unionoidea)

The geographic range of the freshwater naiad Margaritifera auricularia has declined alarmingly since the beginning of the 20th century. The last records of live specimens date from 1933, and this species was thought to be extinct until 1996 when the authors found a population of about 2000 mussels in a channel of the Ebro River basin (Spain). The habitat, biology and host fish of the species are here described for the first time. The habitat is a well oxygenated, subsaline and oligo-mesotrophic water with high values of calcium (150 mg/l) where M. auricularia shows a patchy distribution in a substrate of pebbles, gravels and sand. In aquarium experiments all individuals released glochidia and developing embryos during 35 days (February-March), the former becoming attached to the gill filaments of the sturgeon (Accipenser baeri) 1 day after emission. One month later, at a temperature of 16-20 degrees C, metamorphosed juveniles were obtained from induced infestations on the sturgeons. We review the current situation of this population and measures that should be urgently implemented to conserve this species through conservation of the habitat (Canal Imperial de Aragon) and long term programmes of artificial propagation. (C) 2000 Elsevier Science Ltd. All rights reserved.