Date of Award
5-2025
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Ocean Engineering and Marine Sciences
First Advisor
Richard B. Aronson
Second Advisor
Robert van Woesik
Third Advisor
Brooke Wheeler
Fourth Advisor
Lauren T. Toth
Abstract
Effective coral-reef management and conservation involve adaptively updating approaches based on emerging information. This thesis aims to inform management practices surrounding the zoanthid species Palythoa caribaeorum, which has become increasingly controversial in recent years due to its complex relationship with both living and dead corals, raising questions about its overall impact on coral reefs. In dynamic and fragile coral-reef ecosystems, such as the Florida Keys Reef Tract (FKRT), which is the study area for this project, it is crucial to understand the role of competitive species, like P. caribaeorum. The purpose of this study was to 1) identify the parameters most strongly associated with the distribution of P. caribaeorum and 2) evaluate the relationship between its abundance and key reef-structure attributes, to better understand its potential role in coral-reef restoration. The distribution model indicates that maximum silicate concentration, minimum dissolved oxygen concentration, maximum depth, and minimum temperature are the best predictive factors for the distribution of P. caribaeorum in the Florida Keys. The model also reveals that the Middle Keys are particularly suitable for the species compared with the Lower and Upper Keys, which contrasts with what we know about the distribution of hard corals. Additionally, reef elevation was found to be positively related to the abundance of P. caribaeorum, suggesting that areas with a high cover of P. caribaeorum may contribute to preserving ecosystem functions, such as shoreline protection. This relationship takes on added significance within the context of the FKRT, which is characterized on average by low accretion potential and high erosion rates. As a result, corals along the reef tract are particularly vulnerable to stress and increased erosion from opportunistic species. Although P. caribaeorum competes with living corals for space, the solution to coral-reef degradation is not as simple or straightforward as removing the zoanthid from the reef. First, P. caribaeorum is not easily eradicated, and it quickly recolonizes space following partial-colony removal. Even some of the fastest-growing corals, like Acropora cervicornis, are less successful when in contact with it, which creates an added risk to new Acropora colonies outplanted through restoration. Second, the species has been shown to deter bioeroders and possibly prevent the erosion of dead corals and removing it could destabilize the underlying reef structure. Therefore, removing mats of P. caribaeorum as a part of coral-outplanting efforts should be reconsidered. Instead, managers might prioritize outplanting at sites that have minimal distributional overlap between P. caribaeorum and stony corals.
Recommended Citation
Barcala, Anna Aurora, "Palythoa caribaeorum (Cnidaria: Zoantharia) in the Florida Keys National Marine Sanctuary: Where Management Strategies Meet Ecological Reality" (2025). Theses and Dissertations. 1580.
https://repository.fit.edu/etd/1580