Front cover image for Comparing life history traits and responses to environmental variation between mussel species in the San Saba River

Comparing life history traits and responses to environmental variation between mussel species in the San Saba River

Freshwater mussel species (Unionidae) can vary considerably in their life history traits (e.g., longevity) and mussels with different life history strategies may dominate in different types of habitat. Unfortunately, data on life history traits are still missing for many species, and the factors that determine freshwater mussel distribution along a river are not well understood. Such information, however, is crucial for the conservation of this highly imperiled group of organisms. The objectives of my study were to (1) determine the maximum age and growth constant for three mussel species with different life history strategies; and (2) to perform translocation experiments at two spatial scales (within and between river segments) where mussels were moved to locations from which they were absent to determine if local habitat conditions were limiting their survival and performance. The translocation experiments were carried out in the San Saba River, Texas, using mussels with two different life history strategies (opportunistic and equilibrium). Thin sectioning of mussel shells and analyzing their size in relation to the number of annuli showed that the maximum lifespan differed considerably between species and was highest for Cyclonaias petrina (31 years), lowest for Utterbackia imbecillis (9 years), and intermediate for Lampsilis bracteata (16 years). In contrast, growth constants were rather similar between species. The translocation experiments showed that local habitat conditions are limiting the opportunistic species (U. imbecillis) more strongly than the equilibrium species (C. petrina and pustolosa). Detection was considerably and consistently lower and mortality higher for U. imbecillis that were translocated to a habitat from which they were absent. Responses of C. petrina and C. pustolosa to translocation provided mixed evidence. Although several measures (e.g., mortality and glycogen within the lower segment, growth between segments) indicated that mussels performed better in the control habitat, it was not a consistent pattern. This suggests that other factors, which may affect earlier life stages not tested here, may limit their distribution. Detection of Cyclonaias declined considerably in a treatment pool in the upper segment after a flooding event, whereas it remained high in the upper riffle. Thus, disturbance may play an important role for the distribution of mussels, which should be investigated further by future studies. The study shows that suitable habitat is not necessarily indicated by presence of mussels especially those with different life history strategies, which needs to be considered in relocation efforts
Thesis, Dissertation, English, 2020
Texas State University