Semester of Graduation
Fall 2025
Degree Type
Dissertation/Thesis
Degree Name
Masters in Integrative Biology
Department
Ecolology, Evolution, and Organismal Biology
Committee Chair/First Advisor
Troy Mutchler
Second Advisor
Nick Green
Third Advisor
Joel McNeal
Abstract
Halophila stipulacea (Forsskål & Niebuhr) is a tropical seagrass native to the Red Sea, Persian Gulf, and Indian Ocean. In 2002, invasive populations of H. stipulacea were identified in the Caribbean Sea where it now forms large meadows, displaces native seagrasses, alters invertebrate and fish communities, and potentially affects organic matter dynamics in invaded meadows. This study investigated differences in organic matter dynamics between meadows of H. stipulacea and native Thalassia testudinum within the Jobos Bay National Estuarine Research Reserve (JBNERR) on the southern coast of Puerto Rico. From March 2023-March 2024, sampling was conducted across four sites to investigate the expansion of H. stipulacea, detrital standing stocks in relation to seagrass cover, standing stock of epiphytes between seagrass species, sediment organic matter content across vegetation types, and decomposition rates. Litter bags of green tea, rooibos tea, H. stipulacea, and T. testudinum were used to compare decomposition of the two species. H. stipulacea expanded during the study and potentially displaced T. testudinum at one of the sampling sites. The invasive seagrass supported a lower quantity of epiphytes (H. stipulacea = 0.21 ± 0.42 mg/cm2, T. testudinum = 0.26 ±0.13 mg/cm2, p = 0.01673). H. stipulacea standing stock exhibited a positive trend with detritus standing stock, unlike T. testudinum. H. stipulacea tissues decomposed faster than T. testudinum (H. stipulacea = 0.77 ± 0.17 % loss/day, T. testudinum = 0.48 ± 0.11 % loss/day). No difference was found in sediment organic matter content between vegetation types. Results suggest that if H. stipulacea continues to spread, broader trophic dynamics and carbon cycling mechanisms may be affected, where H. stipulacea decomposes more rapidly and supports fewer epiphytes than dominant native seagrasses, potentially leading to less carbon storage and less energy for epiphytic/live tissue grazers.
Comments
Funded through Puerto Rico Sea Grant