Survival durations and behavioural adjustments of two freshwater bivalves (Unio terminalis, Unionida and Corbicula fluminea, Venerida) under two emersion conditions

Abstract

Freshwater bivalves in shallow waters are often exposed to extended periods of drought and are highly affected due to their limited mobility. Their adaptation to emersion is a key factor for survival, particularly during human-made unnatural water regime fluctuations or short-term droughts. In the current study, survival durations of two freshwater bivalve species (Unio terminalis, Unionidae and Corbicula fluminea, Cyrenidae) were tested under two experimental emersion conditions (presence of water-saturated sediment and without sediment). U. terminalis' mean survival duration more than doubled in the water-saturated sediment treatment (992 h) compared to treatment without sediment (448 h). For C. fluminea, the mean survival duration in the water-saturated sediment treatment (278 h) was over 50% longer than that recorded in the treatment without sediment (174 h). Both species probably made behavioral adjustments according to the environmental conditions to respond to the presence of the water-saturated sediment and maximized their survival chances. In general, U. terminalis survived significantly longer than C. fluminea in both treatments. No effects of size on survival were observed for either species.