Master of Science (M.Sc.)
Michael D. Lamar
The diamondback terrapin (Malaclemys terrapin) is a species of turtle found exclusively in brackish water habitats. Terrapins are currently facing population threats including by-catch mortality in crab pots, predation, and habitat loss. The expansion of the exotic, invasive reed Phragmites australis is causing widespread structural and functional changes to coastal ecosystems throughout North America, which could negatively impact the nesting success of female terrapins by invading preferred nesting habitats. I examined the extent to which Phragmites affects nesting of a breeding population of diamondback terrapins at Fisherman Island National Wildlife Refuge on the eastern shore of Virginia, where Phragmites has recently expanded into known areas of terrapin nesting. With data collected from the 2015 nesting season I quantified the impacts of this expansion on terrapin nesting by: determining the extent to which nest incubation temperature is impacted by Phragmites shading, determining how Phragmites density impacts the risk of rhizome invasion into nests, and determining how the presence of Phragmites impacts predation of terrapin nests. I also examined landscape features to determine which factors may be associated with diamondback terrapin nest site use. I found that Phragmites cover greater than 50% would decrease incubation temperatures of terrapin nests sufficiently to produce predominantly male hatchlings. There was no effect of Phragmites cover on root growth into simulated nests, but cover by other dune plant species explained observed trends in root growth. I did not find a significant effect of Phragmites on nest predator activity, but did find that Phragmites had an impact on terrapin nest site use on Fisherman Island. Distance from nest to nearest marsh and tidal creek also influenced terrapin nest site use. With crab pots and roadways contributing to high adult mortality every year, high nesting success will be highly important to maintaining and propagating this charismatic species.
© The Author
Cook, Cassandra, "Impacts of Invasive Phragmites Australis on Diamondback Terrapin Nesting" (2016). Dissertations, Theses, and Masters Projects. William & Mary. Paper 1477068338.