Paper Type

Master's Thesis


College of Arts and Sciences

Degree Name

Master of Science in Biology (MS)



NACO controlled Corporate Body

University of North Florida. Department of Biology

First Advisor

Dr. Cliff Ross

Second Advisor

Dr. Eric Johnson

Third Advisor

Dr. Daniel C. Moon

Department Chair

Dr. Daniel C. Moon

College Dean

Dr. Barbara A. Hetrick


In the past century, seagrasses have experienced massive die off episodes in what has been collectively referred to as “wasting disease.” Researchers generally agree that wasting disease is caused by a protist of the Labyrinthula genus, and that environmental stressors can make some populations of seagrasses more susceptible to infection. The purpose of this study was to examine the combined effects of elevated salinity, elevated temperature, elevated sulfide and night-time hypoxia on Thalassia testudinum health and its response to Labyrinthula sp. infection under controlled conditions. To test these effects, microcosms were utilized and individual seagrass shoots were randomly assigned to treatment groups consisting of various combinations of abiotic stressors. They were then infected with Labyrinthula sp. and monitored for lesion formation and a reduction in photosynthetic efficiency. It was hypothesized that seagrasses incubated under the application of a given stressor would show evidence of declining health, and, in turn, would be more prone to infection, as quantified by lesion size and reduced photosynthetic capacity. Results indicated that abiotic stressors have little effect on T. testudium’s ability to resist infection from Labyrinthula sp. However, the Labyrinthula sp. was highly sensitive to abiotic stressors, specifically salinity, indicating that the health of the pathogen greatly contributed to the severity of the disease. Therefore, the stress thresholds of both the host seagrass and the pathogen need to be considered. Indeed, the interaction(s) among T. testudinum, Labyrinthula spp. and the environment are complex and not as linear as previously thought.