Corallivory on Hawaiian Reefs
Date
2024
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Abstract
Corallivores, predators of coral, span a wide range of taxa on tropical reefs. Corallivores can affect coral fitness, leading to reduced growth and reproduction, and at high densities, can cause mass coral mortality. As human-made threats to corals escalate and compound the effects of corallivory, coral reef managers increasingly need monitoring tools to track changes in corallivory. Historically, corallivory has been monitored with in situ visual surveys or post-hoc estimates derived from photoquadrats, both methods of which have limitations. Structure from Motion (SfM) photogrammetry, an imagery-based methodology, has emerged as a potential alternative. I counted bite marks by reef fishes on colonies of 16 coral species in paired in situ visual and SfM surveys at sites around Oʻahu to evaluate the accuracy of SfM as corallivory monitoring tool. I found significant differences in bite counts between methods, with SfM detecting higher counts. This disparity was more pronounced at deep sites and locations with high coral cover, reflecting the limitations of SCUBA diving inherent during in situ surveys. However, despite differences in absolute counts, both methods were consistent in qualitative patterns across sites, indicating that SfM is a viable tool to quantify corallivory, with potential for enhanced accuracy. Given the success of this tool, I leveraged the same data to investigate patterns and drivers of corallivory. My analysis revealed consistent consumption of only six coral species by reef fishes. There was also a positive relationship between species-specific coral cover and predation intensity for the preferred coral species of each corallivore, shedding light on common predator-prey interactions. Considering the heightened vulnerability of recently outplanted corals to predation, this information can inform coral restoration methodologies, ultimately yielding more favorable outcomes. Lastly, I studied the feeding ecology of a common corallivore around Oʻahu, the cushion sea star (Culcita novaeguineae), which may be increasing in abundance at some sites, representing a potential local stressor. I tested prey choice by running pairwise comparisons of corals of opportunity from different species and tracking the order of consumption. I used three methods to construct a feeding hierarchy, and across all methods, stars overwhelmingly preferred Pocillopora spp. and rarely consumed Porites spp. These findings indicate which coral species may face increased predation as seastar populations increase, which has implications for local coral restoration efforts and coral community trajectory under future conditions.
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Ecology, Biology, coral predation, coral reef, corallivory, feeding preference, photogrammetry, structure from motion
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188 pages
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