HCNSO Student Theses and Dissertations

Defense Date


Document Type


Degree Name

M.S. Marine Biology

First Advisor

David Gilliam, Ph.D.

Second Advisor

Rosanna Milligan, Ph.D.

Third Advisor

Charles Messing, Ph.D.


In the Caribbean, local and global stressors have driven significant declines in scleractinian coral cover up to 80% in only three decades. Following these declines, phase shifts in benthic community composition have been reported. Shifts towards macroalgal dominance has been the most widely observed case, however, shifts towards octocoral and sponge dominance have also been reported. In Florida, USA, the Florida Reef Tract is an extensive barrier reef system that contains diverse assemblages of corals, sponges, fish, and other taxa. The Southeast Florida Reef Tract (SEFRT) within the Southeast Florida Coral Reef Conservation Area is the northern portion of this system and lies adjacent to the highly urbanized and populated South Florida coastline. Long-term decreases in stony coral cover have been reported for this region, as well as more recent and drastic changes resulting from the Stony Coral Tissue Loss Disease outbreak. With this recent significant loss in stony corals, octocorals have become a more abundant constituent of the SEFRT. Although multiple studies highlight the community composition of local stony corals as well as spatial and temporal changes in their cover, the same has yet to be investigated for the octocoral community. This study investigates spatial and temporal trends in octocoral density, community composition, colony height, and colony condition (i.e. bleaching and disease) from 2013-2018 on the SEFRT. Analyses indicate an increase in density and a decrease in colony height throughout the study period. Both bleaching and disease prevalence remained very low, likely at background levels, during a time period when high levels of bleaching and disease were reported in the stony coral community. Finally, significant spatial variation of the community was observed throughout the SEFRT as density, colony height, and community composition of the outer reef was different from both the inner and middle reefs. These changes do not appear to correlate with events that resulted in the significant decline of stony corals (e.g. thermal anomalies, disease outbreak), suggesting that its drivers may not be similarly impacting the octocoral community. Evidence suggests that this high-latitude reef system can support a high-density octocoral community, but significant spatial variation in density and composition exists. With reefs experiencing dramatic phase shifts, it is imperative to understand the contribution of seemingly resistant organisms, like octocorals, to reef community dynamics.