As native, freshwater mussels continue to decline in the United States, successful conservation and management plans are essential for their survival. Understanding the drivers of native mussel declines, how the ecological roles mussels play within aquatic systems may be affected by declines, and the conservation status of our mussel fauna in different watersheds is critical to inform management and conservation efforts. The Asian clam (Corbicula fluminea, Müller, 1774) is an invasive species found throughout the United States that can reach densities of greater than 1000/m². Given these high densities, Asian clams have been linked to declines in native mussels through hypothesized mechanisms including competition for food and space and depredation of glochidia. Moreover, Asian clams may not fill the same ecological roles as native mussels and could negatively affect the overall health and productivity of a freshwater system because of differences in filter-feeding characteristics and the microorganisms they influence. I conducted a mesocosm experiment using two native mussel species, Plectomerus dombeyanus (Valenciennes, 1827) and Amblema plicata (Say, 1817), to assess the influence of Asian clams on adult mussels and to assess the influence of native mussels and Asian clams on biofilm production from July 2, 2019 to August 28, 2019. I constructed a flow-through system where 30 0.69 m² mesocosms were supplied with constant water flow (1,440 L per day) from Kentucky Lake. My experiment consisted of exposing 8 base mussels (4 of each study species) to varying densities of Asian clams (0, 10, 100, or 1000/m²) or comparable densities of native mussels for 8 weeks. Glycogen content of P. dombeyanus was not affected by density, organism, or their interaction, and A. plicata glycogen levels were not affected by organism. However, A. plicata glycogen levels were influenced by density. Low, medium, and high density treatments had glycogen contents 34%, 14%, and 32% lower than the control, respectively. Additionally, medium density treatments had glycogen contents 18% and 16% higher than the low and high densities, respectively. After week 7, biofilm production was 3 and 1.8 times higher in native mussel tanks compared to control and Asian clam tanks, respectively. My results do not support the hypothesis that Asian clams negatively influence native mussel health, but this question requires further research. Specifically, as Asian clams are often the dominant bivalve in the aquatic systems they have invaded, I suggest for some species, like A. plicata, Asian clams at high and low densities could influence native mussel health negatively. Moreover, my results further elucidate the critical ecological roles, such as biofilm production, mussels play in the systems they inhabit, which I found are not replaced by the Asian clam.
In addition to my controlled experiments, I conducted a descriptive survey of the mussel fauna in the Little River in western Kentucky. I conducted timed-search surveys via snorkeling, bottom view buckets, and tactile searches at 31 sites throughout the Little River and its tributaries. Photo vouchers were taken of live mussels discovered and all shells were collected and identified. I found live specimens of 7 species representing a total of 33 individuals, and I found live mussels at only 7 sites. Mean mussel catch-per-unit-effort (CPUE) was 0.0092/minute and ranged from 0 to 0.11/minute among sites. I collected shell material from 24 species, including 3 species not previously reported from the watershed; shell material was abundant at some sites, but most species were present only as old, weathered shells. A total of 25 mussel species were reported historically from the Little River watershed. My finding of only 7 live species suggests that as much as 75% of the mussel fauna is extirpated. Historical estimates of mussel abundance are not available for any site in the watershed, but my extremely low CPUE estimates combined with the abundance of weathered shells suggest that mussel abundance has declined dramatically and population sizes of remaining species are small. The reasons for mussel declines in the Little River system are unknown. It is necessary to better understand what has led to the loss of mussel fauna within the river before considering this system a candidate for mussel restoration.
Year manuscript completed
Year degree awarded
mussels, Asian clams, invasive species, glycogen, biofilms, mussel survey
Andrea K Darracq
Michael B Flinn
Wendell R Haag
Monte A McGregor
Youngquist, Kiersten, "Effects of the Asian clam, Corbicula fluminea, on native freshwater mussels and biofilms" (2020). Murray State Theses and Dissertations. 177.