Date of Submission

12-6-2018

Document Type

Thesis

Degree Name

Master of Science in Environmental Science

Department

Biology and Environmental Sciences

Advisor

Dr. Roman Zajac

Keywords

Purple salt marsh crab, Transplant studies, Grazing pressure, Salt marsh structure

LCSH

Salt marshes, Spartina alterniflora, Sesarma, Dieback, Ecological assessment (Biology)

Abstract

Salt marshes are important, highly productive ecosystems that provide many ecological benefits, including shoreline protection. Salt marshes were long believed to be driven by bottom up forces, however, recent research has suggested that top down influences may impact the foundation species Spartina alterniflora, and consequently marsh structure. This study looked at patterns of Spartina alterniflora dieback along creek bank areas and assessed Sesarma reticulatum abundance spatially throughout the marsh to improve understanding as to whether Sesarma may be influencing the dieback phenomenon. Dieback was occurring in all three salt marshes studied, at two of those marsh sites the rate of dieback was greater during the 2010-2012 timespan than the 2004-2010 timespan. Rate of dieback was greatest in the marsh site where no field studies were conducted. There were no consistent relationships between dieback occurrence and geomorphological traits of the creek section or the creek bank heading. Spatially, dieback and Sesarma presence were found to overlap at both of the marsh sites where field studies were carried out. Sesarma abundance was greater at bare creek bank sites than creek bank sites with typical vegetation growth. Additionally, abundance was greater during predominantly low tide deployments compared to high tide deployments. Sesarma were found to utilize the high marsh bare areas studied. Transplant studies indicated that grazing pressure is present in the marsh sites studied, and that Sesarma could likely be contributing to this pressure. There are predators of Sesarma within the marsh study sites, further investigation is warranted to determine whether there is an inadequate balance that may be leading to overgrazing of S. alterniflora. The results of this study indicate that further investigation into Sesarma reticulatum dynamics within the marsh sites studied relative to Spartina alterniflora dieback areas could help increase understanding of potential interactions between these species impacting salt marsh structure and potentially long term sustainability. Understanding these potential interactions, and how they may be complicated by events such as climate change, are important for making management decisions to help ensure that these systems continue to persist and provide the services that we rely upon.

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