HCNSO Student Theses and Dissertations

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Defense Date


Document Type

Thesis - NSU Access Only

Degree Name

M.S. Marine Biology

Second Degree Name

M.S. Coastal Zone Management


Oceanographic Center

First Advisor

Amy C. Hirons

Second Advisor

Richard E. Spieler

Third Advisor

David W. Kerstetter


Seagrass habitats are highly productive ecosystems that support marine food webs and provide essential habitat for a variety of species. Seagrass coverages are declining in abundance worldwide. For southeastern Florida in particular, one of the main causes of the decline is disturbance from dredging and removal of substrate. Seagrass beds at three locations in the vicinity of Port Everglades, Florida were assessed for their trophic contribution to the marine organisms in the area. Seagrasses, algae, invertebrates, and vertebrates from the beds were identified and analyzed for stable carbon and nitrogen isotope ratios to determine their contribution as a food source. Significant differences were found in both δ13C and δ15N between both seagrass species and among the three sites. The δ13C of Johnson’s seagrass Halophila johnsonii ranged from -16.28 to -11.27‰ while shoal grass Halodule wrightii ranged from -15.78 to -13.36‰. The δ15N for H. wrightii were more constrained than those of H. johnsonii, 4.69 to 7.08‰ versus 0.80 to 7.86‰, respectively. Neither seagrass species appeared to be a dominant food source for marine organisms at all three study sites. However, the δ13C and δ15N of both seagrass species, Halophila johnsonii and Halodule wrightii, did fall in the fractionation range of potential consumers, -28.78 to -17.11‰ and 1.96 to 12.63‰, indicating that these animals could be ingesting pieces of seagrass while grazing on epiphytes and other primary producers in the area. Epiphytes found on the seagrass blades appeared to be a greater trophic contributor to local organisms. So while the seagrass species in question may not have been major contributors to the diet of many of the local consumers, the seagrasses nontheless played a vital role as habitat for the epiphytes that did serve as a trophic resource in these communities.


This project was funded by a Chancellor’s Faculty Research and Development Grant to Dr. Amy C. Hirons at Nova Southeastern University.

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