Defense Date

12-4-2025

Document Type

Thesis

Degree Type

Master of Science

Degree Name

Marine Science

First Advisor

Dr. David Gilliam

Second Advisor

Dr. Ronen Liberman

Third Advisor

Dr. Richard Ruzicka

Keywords

Coral reefs, Ecosystem shift, Octocorals, Gorgonians, Recruitment

Abstract

Despite significant stony coral mortality, octocoral density has increased on Florida’s Coral Reef (FCR) over recent decades. Specifically, the common sea fan, Gorgonia ventalina, has become a key component of Florida’s octocoral community. However, trends that drive G. ventalina population distribution and growth on FCR are unknown. Here, I analyzed spatiotemporal changes in G. ventalina density and colony height to investigate population variation and responses to disturbances. From 2013-2024, long-term monitoring was conducted annually along permanent belt transects at 46 sites throughout the three regions of FCR: Kristin Jacobs Coral Aquatic Preserve (Coral AP), the Florida Keys (FLK), and the Dry Tortugas (DRTO). Density and colony height were recorded for all G. ventalina colonies along each transect and analyzed over time and across regions and habitat types. To quantify changes in colony size distributions, the coefficient of variation, kurtosis, and skew of the height data were also analyzed. Mean G. ventalina density and colony height varied spatially, with significantly greater mean density in the FLK compared to the other two regions. All regions experienced population stability for the first six years of the study, revealing resistance to marine heatwaves in 2014 and 2015. Following Hurricane Irma in 2017, mean density and colony height did not significantly decrease, though populations on inner reefs in the Coral AP and forereefs in the FLK experienced significant population growth in 2020. This was likely due to the successional state of FCR after Hurricane Irma destabilized substrate and increased space availability, which caused mortality of large colonies but also facilitated recruitment. This recovery was only evident in select habitat types, suggesting that environmental variables unique to these areas may contribute to G. ventalina success. Following the 2023 marine heatwave, mean density significantly decreased on patch reefs, further revealing habitat variability and suggested harsher exposure to thermal stress in shallow water habitats. This decline highlighted vulnerability in a previously stable population due to unprecedented ocean warming. Exploration into site-specific characteristics that influence G. ventalina success is necessary and can be achieved through continuous long-term monitoring, which will further provide substantial knowledge on the expected trajectory of this species and Florida’s benthic assemblage.

ORCID ID

0009-0004-0527-1253

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