River ecology is dominated by flow seasonality imposed by monsoonal rains [43]. Declines in zoobenthos abundance occur during the wet season in many small streams, as spates may initiate catastrophic drift and washout [44]. Riffles are the most stable mesohabitats in many rivers, because their coarse, armored substrates are the least disturbed by floods [45]. Flood size and frequency are important factors limiting populations of European M. margaritifera, and huge floods destroyed several large mussel beds in the rivers of Scotland, UK [46, 47].