Date of Award

Fall 12-2017

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Coastal Sciences, Gulf Coast Research Laboratory

Committee Chair

Dr. Patrick D. Biber

Committee Chair Department

Coastal Sciences, Gulf Coast Research Laboratory

Committee Member 2

Dr. Wei Wu

Committee Member 2 Department

Coastal Sciences, Gulf Coast Research Laboratory

Committee Member 3

Dr. Gregory A. Carter

Committee Member 3 Department

Geography and Geology

Committee Member 4

Dr. Hyun J. Cho

Abstract

Seagrasses are important coastal resources facing numerous stressors, and losses have been documented from local to global assessments. Under the broad theme of habitat loss and fragmentation, a study of historical change in total area and landscape configuration of seagrasses in the Mississippi and Chandeleur Sounds was conducted. Mapping data was collated from a multitude of previous projects from 1940 to 2011.

Comparisons of seagrass area among various studies that used different mapping methods can result in overestimation of area change and misleading conclusions of change over time. The vegetated seagrass area (VSA) data were generalized to a common resolution for further analysis. Spatial configuration of the seagrass landscape was examined through: (1) an exploratory spatial data analysis using seagrass patch size distribution and hot spot analysis, and (2) a core set of seagrass landscape FRAGSTATS metrics and a principal component analysis to identify major pattern. This study demonstrated a comprehensive analysis across spatial and temporal scales and used multiple landscape indices (from habitat, species composition, VSA, patch size distribution, to spatial configuration at patch- and landscape-levels) to provide insights on the pattern and dynamics of the seagrass landscape. A conceptual model of seagrass landscape change based on two principal factors, overall landscape lushness and continuity, was proposed for the Mississippi Sound.

Overall the study area lost seagrasses with contracted spatial extent over the 71-year period, ostensibly due to loss or reduction of protective island barriers and reductions in water quality. The seagrass landscape in the Mississippi Sound exhibited signs of area loss and fragmentation as far back as the 1940-1950s. The landscape in the 1970s was characterized by loss of habitat, loss of seagrass species, the lowest VSA, a faster rate of decline and a higher loss in VSA than before 1970, a low proportion of large-sized patches and their low contribution to VSA, a reduced intensity of hot spots, and a high degree of fragmentation. Recovery of seagrass occurred during the 1980s and 1990s, with the landscape exhibiting characteristics of a more contiguous and more vegetated condition throughout the early 2000s.

ORCID ID

http://orcid.org/0000-0002-8611-1689

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