Graduation Year

2011

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Biology (Integrative Biology)

Major Professor

Susan S. Bell, Ph.D.

Committee Member

David B. Lewis, Ph.D.

Committee Member

David A. Tomasko, Ph.D.

Keywords

landscape, mapping, fine scale, spatial heterogeneity, fragmentation

Abstract

The study documents seagrass patch dynamics over large spatial extents in Tampa Bay, Florida. Using GIS techniques a set of fine scale seagrass maps was created within locations previously identified as "patchy" seagrass or areas of seagrass loss. Thirty randomly selected landscape windows of various extents were mapped for the years 2004, 2006, and 2008 by visualizing 0.3 m resolution color imagery on-screen at a digitizing scale of 1:500 using a minimum mapping unit of 1 m2. Characteristics of seagrass patches and patterns of seagrass change were quantified using area-based and time interval metrics including total seagrass area, percent change in seagrass area, seagrass percent cover, and number of patches. Patterns of change were then reviewed at multiple levels of spatial organization and multiple temporal scales. Results from seagrass mapping generated from the fine scale (1 m2 resolution) and previously-reported broad scale (2.02 ha resolution) mapping approaches were also compared.

The study documented seagrass patches ranging in size from 1 m2 to greater than 10,000 m2. The fine scale mapping data reported a net increase in seagrass cover from 2004 to 2008. However, only 19 landscape windows were either stable in cover or contributed to the gains in seagrass documented during the study. The remaining 11 landscape windows exhibited various temporal patterns in seagrass loss where patch contraction, complete patch mortality, seagrass fragmentation, and seagrass gap formation were all documented. Results from fine scale mapping indicate that the amount of total seagrass patch area represented by locations categorized as "patchy" in broad scale mapping were, on average, 44 percent less than estimated by the broad scale maps. Together these findings provide new information on how different mapping techniques may produce variable views of seagrass dynamic.

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