Shift from clear to turbid phase in Lake Chozas (NW Spain) due to the introduction of American red swamp crayfish (Procambarus clarkii)

Lake Chozas (Leon, NW Spain) until 1997 was a mesotrophic, macrophyte-dominated clear-water lake. The American red swamp crayfish (Procambarus clarkii Girard) was introduced in 1995-96. In 1998, it increased its numbers coinciding with reductions in plant density from 97% to less than 10% surface cover. The removal of submerged vegetation was accompanied by a fast switch from clear to turbid, Microcystis-dominated conditions in the lake. In situ experiments in Lake Chozas using exclosures and enclosures have proved that the red crayfish are efficient predators of macrophytes. This work gives new evidence of the direct relationship between red-crayfish introduction and the shift from clear to turbid conditions in shallow lakes.