Defense Date

8-7-2026

Document Type

Thesis

Degree Type

Master of Science

Degree Name

Marine Science

First Advisor

Andrew Bauman, Ph.D.

Second Advisor

Fraser Januchowski-Hartley, Ph.D.

Third Advisor

Elizabeth Madin, Ph.D.

Keywords

blue carbon, coral reefs, fear effects, grazing halos, marine reserves, Philippines, trophic cascades

Abstract

Predator presence can cause indirect shifts in prey behavior and composition (fear effects), inducing behaviorally mediated trophic cascades (BMTCs) that alter seagrass structure and associated carbon stores. Grazing halos have been identified as indicators of BMTCs and carbon storage due to formation linked to predator-mediated constrained herbivory. Here, I investigated the effects of predator community composition on reef fish communities, foraging behavior, seagrass structure, and their relationship to organic carbon (OC) stocks at varying levels of risk (i.e., within and outside of the halo). This study was conducted across 10 grazing halos in Tubbataha Reefs Natural Park, Philippines— providing a unique study site in being a near pristine, isolated no-take reserve with several grazing halos visible from satellite imagery. Results were consistent with a BMTC, where prey fish community structure was diminished further from reef shelter and foraging behavior shifted from areas of low to high risk. Accordingly, seagrass blade height and percent cover increased in areas with diminished prey fish communities. OC stocks were highest along the halo edge. By combining in situ measurements of OC stocks and satellite imagery of halo presence, total OC stocks in the lagoon were estimated to be 8377.27 - 10127.42 MgC. The results support that predator presence can cause cascading effects on fish community structure, behavior, and macrophyte distribution, thus causing visible changes to the seascape and quantifiable alterations in carbon storage.

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