Date of Award

Spring 5-1-2018

Degree Type


Degree Name

Master of Science in Integrative Biology (MSIB)



Major Professor

Dr. Joseph M. Dirnberger

First Committee Member

Dr. Troy Mutchler

Second Committee Member

Dr. William Ensign

Third Committee Member

Dr. Jared Taglialatela


The sea urchin Lytechinus variegatus is a known grazer of the seagrass Thalassia testudinum, and has been known to denude vast stands of seagrass beds at high densities. Outside of these denudation events, the effects of sea urchins on seagrass are poorly understood. This study examines the effects of L. variegatus on T. testudinum in situ, to understand how sea urchins are affecting seagrasses in situ. Results indicate that urchins were found in the offshore portion of the seagrass bed at densities up to 4 urchins/m2. Changes in temperature and sediment size in the bay indicate that there is a greater exchange rate bay water in the offshore portion of the seagrass bed, and bay water may act as a temperature buffer for urchins in that part of the bed. Urchin movement experiments and dispersion patterns indicate that urchins move more where seagrass cover is low. Field surveys and lab choice experiments indicate that urchins tend to be detrital consumers of seagrass blades rather than herbivores on live seagrass tissue. Together, these results suggest that L. varieagtus densities observed in this study do not appear to have strong negative affects on seagrass beds as has been previously seen in field enclosure experiments and denudation events.