Date Awarded

2015

Document Type

Thesis

Degree Name

Master of Science (M.Sc.)

Department

Virginia Institute of Marine Science

Abstract

Seagrasses modify the coastal areas they occupy by trapping sediments and improving water clarity, providing habitat for marine animals, and cycling nutrients. Populations are in decline worldwide, and in the lower Chesapeake Bay, U.S., Zostera marina populations are decreasing due to poor water quality and high summertime temperatures. Ruppia maritima, a seagrass that is smaller, but has a greater tolerance of high temperatures than Z. marina, is replacing Z. marina in some areas. This study examined bed characteristics and microbial community structures of each seagrass species, as well as mixed assemblages, at three sites in the lower Chesapeake Bay where R. maritima has been replacing Z. marina over recent years. The objective of this study was to determine the potential of R. maritima to ameliorate detrimental effects of Z. marina loss. Samples were taken in June and August of 2013. In contrast to expectations that R. maritima would increase in abundance by August, R. maritima biomass and density decreased. Sediment grain size showed interactions between site and habitat type; two sites of the three showed greater mean fine sediments in Z. marina than R. maritima stands. Where sediment erodibility was measured, eroded mass was greater in the Z. marina sediment compared to the R. maritima sediment in June, while eroded mass was greater in R. maritima sediment in August. This suggests that sediment trapping capabilities may differ seasonally between the two species, with Z. marina generally capable of trapping more fine sediments than R. maritima; however this capability may be affected by location and season. Z. marina provided better quality habitat for epifauna in the early summer, but results from late summer were inconsistent as both species died back. Microbial communities, which affect sediment nutrient cycling, were found to be similar among sediments occupied by both species of seagrass, although the effects of site and month were strong. There was also a greater relative abundance of sulfate reducers in the August samples than the June samples. Overall, the results demonstrate that although the quality of some ecosystem services were greater in Z. marina compared to R. maritima, R. maritima still possessed the ability to provide valuable ecosystem services, and could be considered as a restoration option in the Chesapeake Bay, especially in areas where the potential for Z. marina regrowth is low.

DOI

https://dx.doi.org/doi:10.25773/v5-gct9-0e76

Rights

© The Author

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