Impact of extreme climatic events on unionid mussels in a subtropical river basin

An increase in extreme droughts and floods is expected with current and future climate changes. Such extreme climate events may have long-lasting impact on more sessile organisms, such as unionid freshwater mussels, which are highly imperiled. The objective of our study was to test specific predictions for the impact of an extreme drought in 2011/2012, extreme flooding in 2017, and long-term changes by comparing recent and historical mussel community data from an understudied yet biodiverse region of Texas, USA. Drought had the most detrimental impact leading to community-wide declines, indicated by a significant decline of abundances, species richness and occupied sites. Flooding led to shifts in community composition and spatial distribution. Both severe declines and a distinct community shift occurred over the long-term, where the dominance of species shifted to those more tolerable of disturbance. Saltwater intrusion likely caused a significant increase post-flood of a species known to be tolerant of brackish water ( Glebula rotundata ). The impact of flooding was likely buffered by connectivity with extensive backwater areas, forming large wetlands, which may act as crucial refuges for mussels during extreme climatic events. Thus, protecting wetlands is crucial to protect freshwater mussels and the ecosystem services they provide.