Investigation of the habitat structure of freshwater mussels (Bivalvia, Unionoida) within the Kennebec and Androscoggin River

John Hobbes’15 (Neuroscience).  Bowdoin College. “Investigation of the Habitat Structure of Freshwater Mussels (Bivalvia, Unionoida) Within the Kennebec and Androscoggin River.” John Lichter, advisor.

Project Summary:
As a research group under the Professor John Lichter lab, our focus was to measure the ecological recovery of the Kennebec estuary and the nearshore environment. To acheive this goal, we quantified the recovery of both the river herring species and submerge aquatic vegetation (SAV). River herring, a term for both the alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis) anadromous fish species, are ecological important because they serve as food for both inshore and offshore fish species and distribute nutrients between the two habitats. Submerged aquatic vegetation filters water in a given area and provides habitat for microinvertebrates and macroinvertebrates which are prey to many fish species. To measure river herring recovery we did weekly beach seines at three points along both Abby Point and the Eastern River in order to determine species presence and length over the course of the summer.The recovery of submerge aquatic vegetation was measured by walking around submerged vegetated areas along the Kennebec and Androscoggin River and recording the area using a Trimble Geo XM unit. The data was then placed a map using the Arc Map 10 software, and was compared the previous year’s SAV data coverage.

For my individual summer research, I focused on observing freshwater mussel habitats along several sites of the Kennebec and Androscoggin River to determine if there are any correlations of mussel presence or abundance based on substrate type, host fish availability, and the presence of submerged aquatic vegetation. This information is important because freshwater mussels are currently one the most endangered taxa with only 25% of the 297 species known to have stable populations. Three major contributors to the decline of freshwater mussels are the construction of dams, organic/inorganic river pollution, and overfishing. These human actives resulted in the collapse of aquatic plants, macroinvertebrates, and fish within the Kennebec River, all of which are necessary to maintain healthy mussel populations.

The results showed that habitats consisting of dense mud appear to have a smaller prevalence of mussels compared to areas with silt or sandy substrate types. The sandy substrate habitat appears to have the highest abundance of mussels, although the area mostly consist of the Alewife floater (Anodonta implicata) species.

Another aspect of my research was to determine whether the absence of fossilized freshwater mussel shells is due to historic pollution, which decreased the pH of the Kennebec River years prior. To answer this question I placed mussel shells in historically low pH levels, and observed how they degrade within the solutions. However, my results showed that shell mass did not appear to degrade significantly over time, meaning there is a different variable explaining the lack of a historical mussel presence.


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