Stage-specific responses to freshwater mussels to temperature and suspended solids

Abstract

Elevated levels of suspended solids (TSS) are one of the most widespread water quality problems in streams, rivers, and lakes throughout North America, yet little is known about their effect on populations of freshwater mussels. Freshwater mussels are the most imperiled fauna in the United States and understanding the influences of TSS on their life history will be critical for implementing appropriate conservation action. The overarching objective of my dissertation is to experimentally assess the effect of either temperature or TSS or both on multiple stages of freshwater mussels’ life cycle, including filtration, fertilization, brooding of glochidia (larvae), and mantle lure display. For these experiments, I manipulated pond TSS concentrations at South Auburn Fisheries Research Station, Auburn, AL through the addition of aqueous fertilizer (organic solids) or bioturbating carp (inorganic solids). In-pond filtration trials at warm temperatures, with two lentic species, two lotic species, and one habitat generalist, demonstrated a linear increase for the lentic and generalist species in particle removal with increasing suspended solids up to 50 mg/L, but no relationship for lotic species. However, lotic species particle removal was constrained at high temperatures. Trials during the spawning season showed that <30% of females per pond developed glochidia when suspended solids levels were >20 mg/L. This pattern was consistent across two species, a short- and a long-term brooder, in ponds dominated by inorganic solids and for the long-term brooder in ponds dominated by both organic and inorganic solids. In-marsupial glochidia, showed no difference in viability or metamorphosis rates between low and high TSS ponds. Finally, laboratory experiments with flow-through pond water demonstrated the role of temperatures in regulating mantle lure display and a switch to conglutinate release as a secondary strategy for Ligumia subrostrata. Overall, my results show that TSS appears to have the greatest negative effect on early reproduction, which includes both fertilization and glochidia development. Determining a critical suspended solids threshold (~20 mg/L) where successful reproduction is limited aids in understanding mechanisms responsible for the decline of many mussel species in disturbed watersheds and can guide future restoration and conservation activities.