Date of Award

Summer 8-2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

Program/Concentration

Ecological Sciences

Committee Director

Kent E. Carpenter

Committee Member

David T. Gauthier

Committee Member

Christopher E. Bird

Abstract

The Visayas Region of the Philippines is a global epicenter of marine fish biodiversity. Hypotheses attribute this peak of species richness within the Coral Triangle to processes that occur at geological time scales. However, changes in biodiversity may occur on ecological time scales, allowing for the assessment of the potential impact of anthropogenic activities. Recent declines in genetic, species, and ecosystem diversity have been observed in the tropics, including the Philippines. Within the Philippines the Visayas Region is considered the epicenter of species adversity due to anthropogenic stressors such as habitat degradation, overfishing, and harvesting individuals for the aquarium trade. Human-induced environmental change can alter fish communities and impose strong evolutionary pressures on wild fish populations, however historical baselines are rare in tropical marine systems. This study leveraged three historical baselines from the Philippines to examine spatiotemporal change in reef fish communities and temporal change in genetic diversity of reef fish populations from decadal to centennial scales: 1978 fish visual census survey, 1978–1979 Smithsonian ichthyocide survey, and 1908–1909 RV Albatross survey. Contemporary duplicate surveys provide one of the most comprehensive temporal assessments of reef fish biodiversity change ever assembled for the Philippines. These results show that human-altered environments generate heterogeneous evolutionary trajectories among reef fishes and highlight the value of historical museum collections for identifying genetic, species, and ecosystem diversity changes and vulnerabilities in the face of ongoing environmental change. Reef fish biodiversity in the Visayas is declining across ecological and evolutionary scales, but the magnitude of decline varies by species and habitat. There are widespread declines in species richness, increased community reorganization, and strong habitat-linked structuring. The changes are heterogeneous between seas, sites, and habitats, with some sites exhibiting resilient fish communities and populations. Genetic erosion was observed in a heavily exploited species which may hinder its ability to adapt to environmental change. In contrast, the genetic diversity of several species either remained stable or even increased, suggesting that some reef fishes may better persist in altered environments because of ecological flexibility, connectivity, or demographic resilience. Together, these findings demonstrate that anthropogenic pressures on Philippine reefs have been deep enough to leave detectable ecological and genomic signatures across decades and even centuries.

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DOI

10.25777/5v8e-j928

ORCID

0000-0003-1263-4847

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