21-13 Tracking Sharks’ Responses to Coral Reef Degradation Over Millennia in the Panamanian Pacific Using Fossil Dermal Denticles

Session: Insights from Microfossils and Their Modern Analogs: From Traditional to Emerging Approaches

Presenting Author:

Erin Dillon

Authors:

Dillon, Erin¹, García, Irene², Gómez Benalcázar, María Mercedes³, de Gracia, Brígida⁴, Cybulski, Jonathan⁵, Opazo, L. Felipe⁶, García-Méndez, Kimberly⁷, O'Dea, Aaron⁸

(1) Smithsonian Tropical Research Institute, Panama City, Panama, (2) Smithsonian Tropical Research Institute, Panama City, Panama, (3) Smithsonian Tropical Research Institute, Panama City, Panama; Faculty of Life Sciences, Escuela Superior Politécnica del Litoral, Guayaquil, Ecuador, (4) Smithsonian Tropical Research Institute, Panama City, Panama, (5) Smithsonian Tropical Research Institute, Panama City, Panama; Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island, USA, (6) Departamento de Ecología, Facultad de Ciencias, Universidad Católica de la Santísima Concepción, Concepción, Chile; School of Geology, Faculty of Science, Engineering and Technology, Universidad Mayor, Santiago, Chile, (7) Smithsonian Tropical Research Institute, Panama City, Panama, (8) Smithsonian Tropical Research Institute, Panama City, Panama; Sistema Nacional de Investigación (SENACYT), Panama City, Panama,

Abstract:

Climate change threatens the persistence of coral reefs, which in turn has affected reef-associated predators such as sharks. However, the relationship between reef health and shark abundance remains uncertain, and we know little about how it might shift under future environmental change. This is particularly true in the Tropical Eastern Pacific, where reefs experience large climatic variability. Here, we leverage a past climatic episode in the Panamanian Pacific—a climate-driven slowdown of reef accretion and loss of coral habitat—to assess how shark communities respond to reef degradation following climate stress. The reef collapse, which lasted over 2,500 years (~4.2–1.5 ka), has been well-documented through estimates of reef accretion and analyses of coral community composition in reef matrix cores collected throughout the region. We quantified the accumulation of shark scales (dermal denticles) in cores spanning the last ~6,000 years to reconstruct shark communities before, during, and after the reef collapse at two locations within the Gulf of Panama (Las Perlas Archipelago and Isla Iguana). Dermal denticles were also measured and classified by morphotype to track changes in the functional structure of shark communities through time. Finally, ratios of shark dermal denticles to fish otoliths (ear stones) accumulating in the same samples were used as a proxy of relative trophic structure. Our preliminary data suggest that 1) shark abundances might have decreased during the reef collapse but were able to recover and 2) both the functional structure of shark communities and relative trophic structure remained fairly stable across the event. These results evidence the historical resilience of shark communities during past environmental disturbances along Panama’s Pacific coast, enabling predictions of how different ecological groups of sharks might fare under intensifying fishing and climate impacts in the region.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8291

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