Colossal Aggregations of Giant Alien Freshwater Fish as a Potential Biogeochemical Hotspot

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Boulêtreau, Stéphanie | Cucherousset, Julien | Villéger, Sébastien | Mastrorillo, S. | Santoul, Frédéric

Edité par CCSD ; Public Library of Science -

International audience. The ubiquity and fascinating nature of animal aggregations are widely recognised. We report here consistent and previously undocumented occurences of aggregations of a giant alien freshwater fish, the Wels catfish (Silurus glanis). Aggregative groups were on average composed of 25 (±10 SD, ranging from 15 to 44) adults with estimated average total biomass of 651 kg (386 - 1132) and biomass density of 23 kg m−2 (14 - 40). Aggregations always occurred within the same location. No foraging, reproductive or anti-predator behaviour were observed during the aggregations. A mass-balance model estimated that these colossal aggregations of an alien species can locally release, through excretion only, up to 70 mg P m−2 h−1 and 400 mg N m−2 h−1, potentially representing the highest biogeochemical hotspots reported in freshwater ecosystems and another unexpected ecological effect of alien species

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