Life cycle strategies of Baetis species (Ephemeroptera, Baetidae) in acidified streams and implications for recovery

Chemical recovery of anthropogenic acidified streams is being observed in North Hemisphere countries, while biotogical recovery processes are delayed and appear to be complex. Here, we conducted a one year survey on several Baetis species, a known acid-sensitive genus, highlighting how developmental strategies could influence the presence and abundance of their populations in streams of varying acid levels. We found contrasting sensitivity of Baetis species to acidification, ranging from "very" acid-sensitive (B. melanonyx) and "slightly" acid-sensitive (B. alpinus and B. rhodani) to "acid-benefiting" (B. vernus). The study highlighted that both B. alpinus and B. rhodani showed similar patterns under acidic conditions. Occurrence and abundance appeared unequivocally related to the high level of plasticity of their bivoltine cycle. On the contrary, the univoltine B. vernus and B. melanonyx x demonstrated opposite responses to acidification revealing strong differences in their sensitivity at early stages. Our findings underline the importance of life cycle knowledge in considering species specific responses to freshwater acidification and its implication on the understanding and monitoring of biological recovery processes.