Assessment of the Feeding Ecology of Native and Non-Native Freshwater Bivalves in a North Carolina River Basin
There are several factors that contribute to the decline of freshwater bivalves, including the prevalence of storm water runoff, excess nitrogen inputs, low food quality and the destruction of aquatic habitats. The primary goals of this research were to: 1) characterize the water chemistry and hydrology of three watersheds with different land use characteristics in the Neuse River Basin (NRB), North Carolina, 2) to determine the dominant food sources and potential feeding strategy differences of native and non-native freshwater bivalves that reside concurrently in these habitats and 3) to better understand the efficacy of bivalves as biomonitors of nutrient and sediment contaminants. To address these goals, a combination of methods was utilized, including stable isotope (15N and 13C) analyses, high-resolution water quality monitoring, and a laboratory dose-response experiment with a valve gape sensor.
Chapter 1 results of the long-term (36 month) analyses suggest that dominant watershed type was a predictor of mean 15N values of nitrate (NO3-). Also, mean 15N tissue values of Elliptio complanata from agricultural sites were significantly heavier than urban and forested watersheds, suggesting an assimilation of agricultural nutrient sources. Mean 13C bivalve tissue values were significantly depleted in forested compared to agricultural and urban watersheds. Short-term (3 to 5 day) storm event data indicated that the urban watershed showed greater changes in the quality of bivalve food sources (15N, 13C and C/N of SPOM) with discharge compared to the forested and agriculture watersheds. The combined isotopic and hydrologic data indicated that turbidity and low food quality (C/N > 10) were associated with increased discharge. The implications suggest that native mussels (E. complanata) may assimilate a majority of their food sources during low flow conditions.
Results of the second study showed a significant association between the isotopic composition of bivalve tissue (Corbicula fluminea and E. complanata) and watershed type. The implications are that C. fluminea bivalves may be more sensitive biomonitors than native mussel species of nitrate and suspended solids associated with turbidity found in disturbed watersheds. This study supports previous research and offers new information, which suggests that the decline of native mussel populations may be associated with poor water quality and hydrological conditions unique to urban and agricultural watersheds.
The third phase of this dissertation consisted of a laboratory study that utilized a state of the art valve gape sensor to evaluate feeding activity across distinct turbidity periods modeled after an urban storm event hydrograph. Results suggested that feeding strategies of the non-native bivalve, C. fluminea might be better adapted to tolerate moderate to high turbidity conditions associated with a compressed hydrograph. Conversely, the native mussel, L. radiata may have a disadvantage in frequent turbid environments, and this species may be better adapted in less disturbed watersheds (i.e., forested) where average food quality is higher and suspended solids change significantly less with discharge.
In summary, the results of this dissertation have provided valuable insights into native and non-native bivalve feeding ecology across different watershed types, and this work has generated new directions for future biomonitoring research.
Advisor:Jay F Levine; Steve Rebach; David J DeMaster; William J Showers
School:North Carolina State University
School Location:USA - North Carolina
Source Type:Master's Thesis
Keywords:marine earth and atmospheric sciences
Date of Publication:12/19/2006