Survival durations and behavioural adjustments of two freshwater bivalves (Unioterminalis, Unionida and Corbiculafluminea, Venerida) under two emersion conditions.

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. Freshwater bivalves are often exposed to drought and are highly affected due to their limited mobility. According to the results, the presence of moist sediment during droughts provide protection for the bivalve species used in the study and extended survival durations. Additionally, no evidence was found regarding the effect of size on survival. [ABSTRACT FROM AUTHOR]