Hi everyone, this is the final blog post that I’ll be posting for this REU. All in all, I had a great summer of research and learned a lot, and met a lot of great people (especially my REU fam that I became so close with). Below is the abstract for my summer research symposium that I created.
Freshwater mussel species Quadrula. aurea and Quadrula. petrina have shown a strong decline in population density in Texas during recent years for unknown reasons (Burlakova et al., 2011). Sclerochronology, the study of growth patterns in hard tissues of animals, could help to identify the underlying cause of the decline by reconstructing historical population-wide growth patterns. Such growth patterns can be integrated with climate data to establish the drivers of growth. When using this approach, it is crucial to correctly identify annual increments in the prismatic layer of the mussel shells. Stable isotopes of oxygen (δ 18 O) and carbon (δ 13 C) were used to assess if visually identified increment boundaries on the mussel shells represented annual growth rings. This was done by checking for consistent oscillations of isotope values between growth boundaries. Oscillations in the isotope values likely reflect seasonal climate variation, with previous studies showing higher δ 18 O and δ 13 C values during winter (Versteegh et al., 2011). In this experiment, a computer operated micromill was used to extract carbonate samples along the prismatic growth axis in the shells of five mussel specimens for each species in order to be to be analyzed for their δ 18 O and δ 13 C values. Optimal sample weights were within 170-210µg. A significant correlation was found between δ 18 O and δ 13 C with Q. aurea(r=.69, p=7.85×10 -9 ) suggesting that climate drivers affect δ 18 O and δ 13 C variability alike. However, Q. petrina did not exhibit this correlation. The results showed that the seasonality of the isotopes did not match well with visually identified growth increments on the shell, indicating these might not represent annual growth increments. However, when averaging isotope values within visually identified ring boundaries (and in doing so, assigning a specific calendar year to these isotope values), weak trends were found between temperature and carbon and oxygen isotope values, which is consistent with previously published results (Dettman et al., 1998). The weakness of the trends is possibly due to a small sample size, unclear growth boundaries, boundaries, and the use of air instead of water temperature. From these results, it seems that these species seem to have low potential for use in sclerochronology; however, this shortcoming may be overcome with older specimens and a larger sample size.