Clams Running Dry: Greater Drought Tolerance in the Non-Native Asian Clam (corbicula Complex) Than in the Native European Sphaerium Rivicola

Hydrological droughts driven by climate change threaten freshwater biodiversity, including relatively immobile bivalve fauna, unable to escape from air-exposed areas. Furthermore, they may exacerbate biological invasions by more resistant alien species. We measured survival and behavioural responses (migration following receding water line and burrowing) of the vulnerable native fingernail clam Sphaerium rivicola and the invasive Asian clam (Corbicula complex) to water level reduction and sandy substratum drying in a laboratory setting, to assess their susceptibility to a hydrological drought. Corbicula exhibited higher drought resistance with all clams surviving 15 days of air exposure, whereas S. rivicola reached LT50 (time at which 50% mortality occurred) in 5 days and LT90 (time at 90% mortality) in 8 days. During water level reduction, S. rivicola migrated by crawling downwards to wetter areas and reduced their burrowing depth, whereas Corbicula clams remained in place, burrowing deeper into the sediments. We demonstrate that the invasive Corbicula clams are superior to S. rivicola in surviving air exposure, and their burrowing confers an advantage in drought-prone habitats. In the context of climate change, increased drought frequency and duration may facilitate Corbicula’s dominance and replacement of less drought-resilient native bivalves, such as S. rivicola.