The overall goal of this study was to elucidate the relationship between coral nutrition and the observed prey preferences exhibited by corallivorous butterflyfishes. Fifteen species of coral (thirteen hard, two soft) and stomach/hindgut contents from six species of butterflyfish were analyzed in this study, all collected from the central Saudi Arabian Red Sea. All samples were analyzed for lipid, total-nitrogen (proxy for protein), and ash (proxy for minerals and when combined with lipid data, allows for calculation of carbohydrate). Unfortunately, substantial errors were encountered in the experimental lipid data, precluding the use of this data set. Using the value of (protein/ash) as a proxy for potential nutritional quality, it was determined that Pocillopora cf. verrucosa and P. damicornis have the highest nutritional quality, while Acropora hyacinthus and Stylophora pistillata have intermediate nutritional quality, and all remaining 11 species have low nutritional quality. This suggests that the high nutritional quality of Pocillopora damicornis and Acropora hyacinthus may be the cause of the well documented predator preferences for these two species. Fish gut content samples were, on average, twice as rich in protein and half as rich in minerals as the coral tissue samples, suggesting either selective consumption of especially rich parts of the coral colony, or consumption of other food sources (facultative corallivores). In all six butterflyfish species, stomach content samples were consistently richer in protein and poorer in mineral content than the hindgut content samples; this suggests significant and measureable uptake of protein in the butterflyfish digestion process.

Parrotfishes (Scarinae) are dominant Caribbean herbivores that play an important role in reducing coral-algae competition by grazing algae; yet some species are also occasional coral predators (corallivores) and thereby can have direct negative impacts on coral growth and survivorship. There is concern that parrotfish corallivory may contribute to substantial long-term declines in targeted coral species, particularly in areas with a high biomass of parrotfishes and low cover of corals. However, the capacity of target coral species to heal from parrotfish predation and the ecological drivers of corallivory are poorly understood. In Chapter 1, we examined the patterns of coral healing from parrotfish predation scars on Orbicella annularis – an ecologically important framework building coral that is one of the most intensely grazed Caribbean coral species and an endangered species. While some researchers have suggested that parrotfishes may have significant long-term impacts on heavily targeted species such as O. annularis, the patterns of coral recovery from parrotfish predation scars remain poorly understood. To address this knowledge gap, we tracked the fate of parrotfish bite scars on O. annularis colonies across two Caribbean islands for up to two months. We evaluated differences in coral healing between islands in response to a number of variables including the initial scar surface area, scar abundance per coral colony, colony surface area, and water depth. We used these data to develop a predictive model of O. annularis tissue loss from recent parrotfish bite scars. We then applied this model to surveys of the distribution of bite scars at a point in time to estimate long-term tissue loss of O. annularis colonies from a standing stock of bite scars. Our findings suggest that the initial scar surface area is one of the most important predictors of coral tissue loss. The data also indicate that there are thresholds in patterns of coral tissue regeneration: we observed that small scars (≤1.25 cm2) often fully heal, while larger scars (≥8.2 cm2) had minimal tissue regeneration. The vast majority of observed scars (~87%) were 1.25 cm2 or less and our model predicted that O. annularis colonies would regenerate nearly all the corresponding scar area. In contrast, while scars greater than or equal to than 8.2 cm2 were infrequent (~6% of all observed scars), our model predicted that these larger scars would account for over 96% of the total tissue loss for grazed colonies. Overall, our results suggest that the immediate negative impacts of parrotfish predation on coral tissue loss appear to be driven primarily by a few exceptionally large bite scars. While further work is needed to understand the long-term impacts of corallivory and quantify the net impacts of parrotfish herbivory and corallivory on Caribbean coral reefs, this study is an important step in addressing factors that impact the recovery of a heavily targeted and ecologically important Caribbean coral from parrotfish predation. In Chapter 2, we examined the ecological drivers of corallivory across all coral taxa and across three regions of the Greater Caribbean – the Florida Keys, St. Croix, and Bonaire. To do so, we observed how parrotfish grazing intensity varied using both size and abundance-based metrics across multiple spatial scales. At the reef community and regional scale, we found no effect of the biomass of corallivorous parrotfishes or the percent cover of target coral species on the intensity of parrotfish corallivory. However, at the scale of individual coral colonies, we found that coral taxa and colony size were important predictors of corallivory intensity, and that predation intensity increased as colony size increased. Our findings suggest that previous assertions that conservation of corallivorous parrotfishes may have net negative impacts on coral communities, particularly as live coral cover declines, are not supported at the reef-scale. Instead, our research suggests that colony-level traits such as coral taxa and colony size may be stronger drivers of predation intensity. Additionally, our research suggests that parrotfishes do not heavily graze upon the majority of coral species, but have a higher level of grazing intensity on three taxa, Orbicella annularis, Porites astreoides and other Porites spp. across multiple regions of the Caribbean. Therefore, the direct consequences of parrotfish corallivory for coral tissue loss are likely low for the majority of coral species, but further research is needed to better understand the ultimate causes of selective predation and the long-term consequences of corallivory for heavily targeted coral taxa.

With increasing coastal development along southeastern Florida, nearshore coral reef communities are at an increased risk from anthropogenic impacts. Impact minimization and mitigation efforts associated with permitted coastal construction activities generally exclude nearshore small (< 10 cm diameter) Siderastrea siderea colonies from required coral transplantation due to an assumed high colony mortality associated with transplanting small stony corals. This study evaluated the efficacy of transplanting these small colonies by monitoring survival, growth, and zooxanthellae density post transplantation to an offshore reef area. Unexpected observations of parrotfish predation on the newly transplanted corals were made within the first 24 hours. Within 2 weeks, 94% of the transplants were affected and exhibited recent parrotfish grazing scars. A duplicate transplantation attempt was made at an alternate offshore reef area; however similar results were produced. Due to the high extent of colony tissue loss caused by parrotfish, the initial transplantation effort was repeated with the addition of partial cages to exclude large parrotfish. Zooxanthellae density analysis of the caged colonies revealed an adaptive capability of S. siderea to transplantation as one year post-transplantation, algal densities of the transplanted colonies reflected those of surrounding in situ colonies. A second component of this study investigated if transplantation alone was a direct cause for high predation by examining predation intensity and long-term survival for both transplanted and undisturbed small S. siderea colonies, as well as transplanted Dichocoenia stokesii and Porites porites colonies. Siderastrea siderea colonies were collected from areas surrounding the offshore transplant site and given various stress levels prior to being attached into the transplant grid inter-mixed with colonies transplanted from the shallow nearshore site. All colonies in the transplant grid were placed randomly to eliminate spatial bias. Some nearshore S. siderea transplants were partially caged for 80 days to provide a moderate acclimation period. Many non-caged transplanted colonies suffered some degree of parrotfish predation within 1 week post-transplantation, suggesting that transplantation alone did increase corals susceptibility to predation. However, predation intensity was significantly higher on S. siderea transplanted from nearshore than all in-site transplanted and undisturbed S. siderea colonies from the offshore transplant area. Despite minor parrotfish predation on the offshore in-site transplanted colonies, many displayed long term growth and survival. Partial cages were successful in excluding large parrotfish; however once removed, predation intensity was similar to the non-caged nearshore transplants. Predation on the transplants was selective across both species and place of origin. These results suggest that parrotfish differentiated between transplanted colonies and preferred nearshore S. siderea and P. porites transplants. Findings in this study may aid southeastern Florida resource managers as transplantation activities are frequently utilized due to coastal construction and vessel groundings. The impact of parrotfish corallivory on coral growth and survival should be of higher regard in the light of increasing threats to coral reefs.

Coral reefs are one of the world’s most diverse yet heavily impacted marine ecosystems. As a result of many direct and indirect stressors, coral reefs have experienced major degradation over the last several decades. Declines in coral reefs in the Caribbean have been particularly acute and generally associated with the loss of key herbivores and an increase in algae. Herbivorous fishes such as parrotfishes can positively impact coral reefs by removing algae that compete with corals for light and space. However, many parrotfishes are also important coral predators. Predation on corals, known as corallivory, can adversely affect coral growth, reproduction and survivorship. In this time of changing environments and coral reef decline, understanding the context-dependent nature of parrotfish foraging behavior is of critical importance to scientists and managers. Knowledge of the responses of parrotfishes across a range of resource abundance will help scientists and managers better predict the impacts that these herbivores have on benthic communities as both herbivores and corallivores. In Chapter 1, we examined how six different species of coral reef herbivores (i.e. parrotfishes), all of which belong to a single feeding guild but represent a range of dietary specialization, respond to changes in the abundance of preferred food items. We conducted behavioral observations of parrotfishes in two regions of the Greater Caribbean, and compared consumption rates, diet preferences, and foraging territory size in relation to natural variation across sites in preferred resource abundance. We found that the more-specialized parrotfishes increased their dietary specialization, had smaller foraging territories, and increased their feeding rate with increased preferred resource abundance. In contrast, less-specialized species exhibited constant foraging traits regardless of the abundance of their preferred resources. This study suggests that differences in dietary preference, specialization, and subsequent nutritional demand may drive a differential response in foraging behavior by generalists and specialist herbivores to changes in resource abundance. Recognizing that generalists and specialists differ in the degree to which their foraging behaviors are context-dependent can allow researchers to better predict how herbivores shape the structure and function of marine and terrestrial ecosystems. In Chapter 2, we determined if and how corallivory rates and intensity by parrotfishes differ between two regions of the Greater Caribbean that vary in coral and parrotfish community composition and abundance. We found that more species of parrotfishes than previous studies suggest contribute to corallivory. However, corallivory rates and selectivity for coral species by parrotfishes were largely context-dependent, particularly with regards to the relative abundance of preferred corals and diversity of corallivores at a given site. Although we found that corallivory rates decrease with coral cover, it appears that areas of low coral cover may have high corallivory intensity and coral tissue loss, in part due to the relatively high abundance of corallivores in these areas. The impact of high corallivory intensity and tissue loss requires further knowledge regarding the fate of bite scars on corals.This information will help predict the positive and negative consequences of parrotfishes on coral persistence in the Caribbean. Evidence provided in this thesis furthers our understanding of the dual role of parrotfishes as herbivores and corallivores. Additionally, it reveals the implications of changing coral reef habitats on parrotfish behavior and subsequent coral reef health and resilience.