McGill University
Ph.D. candidate
Supervisor: Frederic Guichard
Dr. Henri Vallès, University of the West Indies, Barbados
Start: 2024-01-01

Project

The Role of Herbivory in Mediating the Net Impact of Marine Protected Areas on Coral Reef Health
Coral reefs are essential marine ecosystems, yet they are increasingly vulnerable to significant and often irreversible shifts from coral-dominated to algal-dominated states, driven by anthropogenic influences such as nutrient enrichment from terrestrial runoff and overfishing. These changes result in significant ecosystem degradation, as reversing the shift to algal dominance is notoriously difficult. Herbivory plays a critical role in maintaining coral health by preventing macroalgal overgrowth, sustaining coral recruitment, and stabilizing reef ecosystems. The absence of herbivores, such as parrotfish, leads to unchecked algal growth, limiting coral recovery. Marine Protected Areas (MPAs) have been implemented worldwide to reduce fishing pressure and promote ecosystem resilience by restoring herbivore populations. However, evidence about the effectiveness of MPAs in promoting coral recovery and resilience remains mixed. While MPAs can increase herbivore biomass, some studies suggest their impact on coral recovery is less significant, especially in areas where ocean warming is the main stressor. A major limitation in understanding the relationship between MPAs, herbivory, and coral health is the lack of experimental research that can disentangle cause-and-effect relationships from confounding environmental variables. This research will contribute to marine ecology by evaluating how herbivory interacts with MPAs to promote coral resilience. It builds on the foundational work of my master’s thesis, which identified herbivory’s importance in controlling macroalgae but was limited to small-scale observations. The study will use experimental exclusion methods and field surveys to address knowledge gaps regarding the role of herbivory in reef recovery and ecosystem management and assess the net impact of MPAs on coral resilience through herbivory. Objectives and Hypotheses The primary objective of this research is to investigate the interactions between MPAs and herbivory in promoting coral resilience. Key research questions include: • How do MPAs and herbivory interact to promote coral health and recovery? • What is the direct impact of herbivory on coral recovery, and do MPAs improve reef health by enhancing herbivore populations? • What level of herbivory is required to maintain coral dominance, and can this level be achieved within MPAs? Hypothesis: MPAs that enhance herbivory will promote coral recovery by suppressing algal growth, facilitating coral recruitment, and maintaining ecosystem balance. Research Approach and Methodology This research will combine a global meta-analysis with experimental field studies in Barbados to evaluate the ecological dynamics between herbivory, MPAs, and coral health. • Global Meta-Analysis: A systematic meta-analysis following the PRISMA methodology will be conducted to synthesize experimental research on MPAs and herbivory. From an initial pool of 1,448 articles, 48 studies have been selected based on their relevance to coral cover, herbivore biomass, and algal suppression. This analysis will identify key factors that determine the success of MPAs in enhancing coral resilience and provide insights into experimental methods that effectively control for confounding variables. • Field Experiments in Barbados: Fieldwork will be conducted along the west coast of Barbados, focusing on the Folkestone Marine Reserve and adjacent areas. The experimental design involves using exclusion cages to manipulate herbivory at MPA and non-MPA sites. Large herbivores, such as parrotfish, will be excluded from specific coral plots to assess their direct impact on the recovery of Acropora palmata fragments. Comparative surveys will measure coral cover, algal biomass, and herbivore density across fishing pressure gradients. • Ecological Modeling and Large-Scale Surveys: Ecological models will be used to predict how herbivory-mediated processes influence coral recovery on larger spatial scales. Surveys along fishing pressure gradients will quantify herbivore biomass thresholds necessary for maintaining coral dominance. This approach will evaluate whether current MPA management strategies are sufficient to meet these thresholds and promote reef resilience. Significance to Marine Ecology This research will advance our understanding of the ecological mechanisms underlying coral reef resilience by demonstrating how MPAs and herbivory interact to maintain coral-dominated ecosystems. The study will provide evidence-based recommendations for MPA management, particularly in the Caribbean region, where the depletion of large herbivores has contributed to ecosystem degradation. By identifying critical herbivory thresholds, this research will help policymakers design more effective conservation strategies that align with broader environmental goals. The study will also address knowledge gaps in MPA effectiveness by integrating experimental and observational approaches. Previous research has highlighted the crucial role of herbivory in maintaining coral dominance and preventing irreversible phase shifts. Unlike my master’s thesis, which focused on small-scale observational studies, this project emphasizes experimental exclusion methods to assess herbivory’s causal impact on coral recovery. The findings will contribute to the design of adaptive MPA policies that consider herbivory as a key factor in coral reef conservation.

Keywords

coral-algal dynamics, marine protected areas, herbivory, ecosystem resilience, trophic regulation, sustainable management, climate change impacts, coral recovery, coral reef conservation