Biofiltration by an imperilled freshwater mussel: implications for water quality in a drying climate

Abstract Freshwater mussels are keystone species in freshwater streams, providing important ecosystem services, including biofiltration. While most research has focussed on Unionidae mussels in northern hemisphere perennial rivers, far less is known about the biofiltration capacities of Hyriidae mussels, which are prevalent in intermittent rivers in arid and semi-arid regions of the southern hemisphere. This study examined biofiltration of the imperilled Australian hyriid, Westralunio carteri . We estimated biofiltration capacity by measuring reduction in algal concentration across three temperatures (15, 20 and 25 ºC) under laboratory conditions. We then validated these laboratory results with field experiments using natural seston. Westralunio carteri exhibited a mean clearance rate of 177.5 (95% CI 125.4–229.7) mL/g dry tissue/hour in the laboratory and 210.9 (95% CI 171.6–250.2) mL/g dry tissue/hour in the field. Clearance rate increased with temperature, with maximum rates recorded at 25 ºC, and smaller mussels had higher mass-specific clearance rates. Clearance rate estimates aligned with rates in other hyriid mussels. Given its biofiltration capabilities, W. carteri may aid in maintaining water quality in intermittently flowing rivers of south-western Australia, where decreasing streamflow due to climate change is increasing the duration of drying in smaller, warmer and increasingly isolated refuge pools.