Tsakiris, Eric Theodore (2016-04). Conservation and Management of Freshwater Mussels (Bivalvia: Unionidae): Reproduction, Non-Invasive Techniques and Relocation. Doctoral Dissertation.
Thesis
Freshwater mussels (Bivalvia: Unionidae) represent one of the most endangered groups of aquatic organisms worldwide, yet efforts to mitigate the endangerment of this group are being outpaced by the rapid decline of species diversity. In this dissertation, I report on advancements to several methods used in conservation of freshwater mussels. First, I validated a non-lethal syringe technique used to quantify gamete production by extracting fluid from gonads. I specifically tested: (i) if gamete traits (sperm concentration, egg size and egg concentration) measured using the syringe technique were correlated with gamete traits measured using a histological technique; and (ii) if survival, growth and body condition (Fulton's K index) were affected by the syringe technique in a two-year mark-recapture field experiment. Gamete production measured over the first year of the study indicated that gamete estimates were positively correlated among techniques, and overall, the syringe technique had no discernible effect on survival probability, shell growth and Fulton's K index of mussels. Being both accurate and noninvasive, this technique can now be used to study the reproductive biology of threatened and endangered mussels quantitatively. Second, I reciprocally transplanted mussel populations within the same river and tested: (i) whether individual and population traits (i.e., survival probability, shell growth and reproduction) successfully acclimated to novel environments, and (i) which environmental conditions best explained seasonal variability in mussel performance? Mussels generally acclimated to the conditions of the sites such that performance was not greatly diminished, but the minor effects that were observed, which originated from environmental and genotypic interactions, suggested some degree of local adaptation was apparent. Cumulative degree days, chlorophyll a and benthic organic matter were among the most import variables explaining trends in survival, growth and body condition; while, cumulative degree days, chlorophyll a and historical discharge were important in explaining gametogenic periodicity. Although mussels responded positively to relocation, my results suggest that resource managers should minimize geographic distances and ecological differences between sites to avoid relocating mussels to populations where variation in demographic phenotypes might hinder relocation success. Future research should investigate the roles of phenotypic variation and habitat quality in driving performance of relocated populations and, ultimately, success of mussel relocations.
