Movement behavior of Unionid mussels in Central Texas
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Freshwater mussels are one of the most imperiled groups of aquatic organisms. Burrowing and horizontal movement of freshwater mussels are behaviors integral to their ecology, yet mussel behavior is still relatively understudied. Thus, more insight into mussel behavior is needed to establish effective survey protocols and to inform the development of long-term conservation strategies. My objectives were to 1) examine and compare burrowing depth in the field among species and sites in the Guadalupe and San Antonio Rivers; 2) examine the effect of (a) differences in species, (b) decreases in temperature and (c) different substrates on burrowing behavior in experimental studies; and 3) examine the effect of dewatering on movement behavior. Seasonal differences were found at two sites in the San Marcos and Guadalupe River, with more mussels burrowing deeper in winter. In contrast, this was not observed at a predominately sandy site in the San Antonio River, where mussels burrowed significantly deeper compared to the other gravel/cobble dominated sites, independent of season. Lab experiments showed that differences in substrate affected burrowing behavior, and mussels responded to temperature changes. Burrowing depth was significantly deeper in sand compared to gravel. Further, when temperature was decreased from above 20°C to 15°C, 9% of the mussels stopped burrowing in sand but 58% stopped in gravel. Significant differences between species were only found in lab experiments with sand, in which Amblema plicata burrowed significantly deeper than Quadrula aurea. Horizontal movement rates differed significantly when comparing dewatering manipulations. At the fastest dewatering manipulation (15 cm/6 hours), 100% of the mussels became stranded, whereas 20 to 30% became stranded during slow (5 cm/10 days) and moderate (10 cm/4 days) dewatering manipulations. Thus, mussels in Central Texas may not have the ability to respond fast enough when water levels change rapidly, i.e., due to operations of dams. Our results also suggest that surveys may need to follow different guidelines depending on local conditions.