Changes in community composition of riverine mussels after a severe drought depend on local conditions: a comparative study in four tributaries of a subtropical river

The frequency and intensity of droughts are predicted to increase over the next few decades and understanding the impacts of drought on mussels is imperative for species conservation. Our objective was to examine the impacts of an exceptional drought in 2011 on mussel communities in four tributaries of the Colorado River basin in central Texas by testing hypotheses that post-drought community composition depends on (1) relative abundances pre-drought, (2) life history strategy of the mussels, (3) ability of sites to retain water, (4) changes in temperature and discharge. Surveys were conducted pre- (2005–2011) and post-drought (2017) and environmental conditions during the drought were examined using discharge data, satellite imagery, and water temperature estimations. No mussels were found at 9 out of 30 sites where mussel populations were present pre-drought. The most abundant species pre-drought tended to be the most abundant species post-drought and no significant difference between life history strategies was found. No clear effect of the ability of a site to retain water was detected, but the largest declines in species richness occurred in the tributaries with the lowest mean discharge and highest water temperatures, suggesting that mussels may be especially at risk in rivers with lower discharge.