Publication Date
Spring 2025
Abstract
Coral reefs along the Caribbean coast of Panamá have experienced a phase shift from coral dominance to macroalgae dominance in the past half century. The increase in algal coverage and ensuing coral degradation is thought to be associated with the 1983/1984 mass mortality event that decimated populations of the keystone herbivore Diadema antillarum. The algal phase shift has been exacerbated by the overfishing of herbivorous Caribbean reef fish. Since the 1983 die-off event, there has been some indication that small herbivorous fish and short-spined urchin species, which can evade fishing pressure, are now the most significant algal grazers in reef communities along the Caribbean coast of Panamá. However, little research has been done on the abundance and diversity of herbivorous fish and small urchins in Guna Yala, the center of marine biodiversity on the Panamanian Caribbean coast. Furthermore, D. antillarum populations have not been surveyed in the area for 10 years, despite evidence of a second mortality event beginning in the Caribbean in 2022. This study investigates herbivore density, diversity, and composition at 5 shallow reef sites around Isla El Porvenir, Guna Yala. 2,880 m2 of reef were surveyed. Data on the substrate composition at each site was collected using randomly placed threaded quadrats. Focal surveys were conducted to assess the average grazing rate of prominent herbivorous fish species. A total of 7 herbivorous fish genera (Acanthuridae, Scarus, Sparisoma, Stegastes, Abudefduf, Microspathodon, Chromis) and 3 urchin species (Diadema antillarum, Echinometra viridis, Echinometra lucunter) were detected throughout the five sites. Diadema antillarum was observed to have a density of 0.031 m2, which is unchanged from the most recent survey conducted in 2015. Stegastes was the most abundant herbivore species (0.438±0.009/m2), followed by E. viridis (0.336±0.021/m2) (p< 0.05). Accounting for bite rate, however, Stegastes exerted similar grazing pressure to other herbivorous fish. Spearman’s correlation analysis revealed a strong, positive relationship between live hard coral coverage and herbivore density (p< 0.05). Algal coverage and herbivore diversity were unrelated. Herbivore diversity and substrate diversity were also unrelated. These results provide evidence that D. antillarum populations have remained stable since 2015, showing no indication of further recovery. Instead, E. viridis and herbivorous fish, particularly Acanthuridae and Stegastes, were found to exert the highest grazing pressure at the five studied reef sites. The results also demonstrate a relationship between live coral coverage and herbivore density, emphasizing the important connection between herbivore population maintenance and coral health.
Disciplines
Life Sciences
Recommended Citation
Fithian, Eleftheria Ellie, "Composition, diversity, and abundance of algal grazers at five reef sites around Isla El Porvenir, Guna Yala" (2025). Panama: Tropical Ecology, Marine Ecosystems, and Biodiversity Conservation. 7.
https://digitalcollections.sit.edu/pne/7