Littérature scientifique sur le sujet « Corallivoria »

AbstractA suite of processes drive variation in coral populations in space and time, yet our understanding of how variation in coral density affects coral performance is limited. Theory predicts that reductions in density can send coral populations into a predator pit, where concentrated corallivory maintains corals at low densities. In reality, how variation in coral density alters corallivory rates is poorly resolved. Here, we experimentally quantified the effects of corallivory and coral density on growth and survival of small colonies of the staghorn coral Acropora pulchra. Our findings suggest that coral density and corallivory have strong but independent effects on coral performance. In the presence of corallivores, corals suffered high but density-independent mortality. When corallivores were excluded, however, vertical extension rates of colonies increased with increasing densities. While we found no evidence for a predator pit, our results suggest that spatio-temporal variation in corallivore and coral densities can fundamentally alter population dynamics via strong effects on juvenile corals.

Corallivorous Drupella (Muricidae) snails at Koh Tao are reported to have extended their range of prey species following a major coral bleaching event in 2010. Populations of their preferred Acropora prey had locally diminished in both size and abundance, and the snails had introduced free-living mushroom corals in their diet. Although the coral community largely recovered, the Drupella population grew and reached outbreak proportions. For this study, corallivorous muricids at Koh Tao were studied more intensively to examine their identities, distribution and prey choice four years after the bleaching event. Drupella rugosa was identified as the major outbreak species and occurred at densities > 3 m-2 in depth ranges of 2-5 and 5-8 m. The density of D. rugosa was related to the live coral cover, Acropora colony density, and depth. Resource selection ratios revealed that species of Acropora, Psammocora and Pavona corals were attacked more frequently than would be expected based on their availability. Strikingly, fungiid corals were now avoided as prey in the recovered coral community, despite them being part of the preferred diet directly after the bleaching. Although D. rugosa showed a clear prey preference, it appears to be plastic by changing with prey availability. The muricids Drupella margariticola and Morula spinosa occurred in much lower densities and were less often associated with corals. Snails of the opportunistic corallivore D. margariticola usually co-occurred in D. rugosa aggregations, although they also formed feeding aggregations by themselves. Whether M. spinosa generally associates with corals as a corallivore or a scavenger has yet to be determined. Molecular analyses did not reveal cryptic speciation among snails sampled from different coral hosts and also no geographic variation. The present study also showed that corallivory is more common among D. margariticola and M. spinosa than previously known.

The diversity of fishes on coral reefs is influenced by the evolution of feeding innovations. For instance, the evolution of an intramandibular jaw joint has aided shifts to corallivory in Chaetodon butterflyfishes following their Miocene colonization of coral reefs. Today, over half of all Chaetodon species consume coral, easily the largest concentration of corallivores in any reef fish family. In contrast with Chaetodon , other chaetodontids, including the long-jawed bannerfishes, remain less intimately associated with coral and mainly consume other invertebrate prey. Here, we test (i) if intramandibular joint (IMJ) evolution in Chaetodon has accelerated feeding morphological diversification, and (ii) if cranial and post-cranial traits were affected similarly. We measured 19 cranial functional morphological traits, gut length and body elongation for 33 Indo-Pacific species. Comparisons of Brownian motion rate parameters revealed that cranial diversification was about four times slower in Chaetodon butterflyfishes with the IMJ than in other chaetodontids. However, the rate of gut length evolution was significantly faster in Chaetodon , with no group-differences for body elongation. The contrasting patterns of cranial and post-cranial morphological evolution stress the importance of comprehensive datasets in ecomorphology. The IMJ appears to enhance coral feeding ability in Chaetodon and represents a design breakthrough that facilitates this trophic strategy. Meanwhile, variation in gut anatomy probably reflects diversity in how coral tissues are procured and assimilated. Bannerfishes, by contrast, retain a relatively unspecialized gut for processing invertebrate prey, but have evolved some of the most extreme cranial mechanical innovations among bony fishes for procuring elusive prey.

Corals are in decline worldwide due to local anthropogenic stressors, such as nutrient loading, and global stressors, such as ocean warming. Anthropogenic nutrient loading, which is often rich in nitrate, inhibits coral growth and worsens corals’ response to warming while natural sources of nitrogen, such as ammonium from fish excretion, promotes coral growth. Although the effects of nutrient loading and ocean warming have been well-studied, it remains unclear how these factors may interact with biotic processes, such as corallivory, to alter coral health and the coral microbiome. This study examined how nitrate vs. ammonium enrichment altered the effects of increased seawater temperature and simulated parrotfish corallivory on the health of Pocillopora meandrina and its microbial community. We tested the effects of nitrogen source on the response to corallivory under contrasting temperatures (control: 26 °C, warming: 29 °C) in a factorial mesocosm experiment in Moorea, French Polynesia. Corals were able to maintain growth rates despite simultaneous stressors. Seawater warming suppressed wound healing rates by nearly 66%. However, both ammonium and nitrate enrichment counteracted the effect of higher temperatures on would healing rates. Elevated seawater temperature and ammonium enrichment independently increased Symbiodiniaceae densities relative to controls, yet there was no effect of nitrate enrichment on algal symbiont densities. Microbiome variability increased with the addition of nitrate or ammonium. Moreover, microbial indicator analysis showed that Desulfovibrionaceae Operational taxonomic units (OTUs) are indicators of exclusively temperature stress while Rhodobacteraceae and Saprospiraceae OTUs were indicators of high temperature, wounding, and nitrogen enrichment. Overall, our results suggest that nitrogen source may not alter the response of the coral host to simultaneous stressors, but that the associated microbial community may be distinct depending on the source of enrichment.

In spite of growing evidence that climate change may dramatically affect networks of interacting species, whether—and to what extent—ecological interactions can mediate species' responses to disturbances is an open question. Here we show how a largely overseen association such as that between hydrozoans and scleractinian corals could be possibly associated with a reduction in coral susceptibility to ever-increasing predator and disease outbreaks. We examined 2455 scleractinian colonies (from both Maldivian and the Saudi Arabian coral reefs) searching for non-random patterns in the occurrence of hydrozoans on corals showing signs of different health conditions (i.e. bleaching, algal overgrowth, corallivory and different coral diseases). We show that, after accounting for geographical, ecological and co-evolutionary factors, signs of disease and corallivory are significantly lower in coral colonies hosting hydrozoans than in hydrozoan-free ones. This finding has important implications for our understanding of the ecology of coral reefs, and for their conservation in the current scenario of global change, because it suggests that symbiotic hydrozoans may play an active role in protecting their scleractinian hosts from stresses induced by warming water temperatures.

Cumulative anthropogenic stressors on tropical reefs are modifying the physical and community structure of coral assemblages, altering the rich biological communities that depend on this critical habitat. As a consequence, new reef configurations are often characterized by low coral cover and a shift in coral species towards massive and encrusting corals. Given that coral numbers are dwindling in these new reef systems, it is important to evaluate the potential influence of coral predation on these remaining corals. We examined the effect of a key group of coral predators (parrotfishes) on one of the emerging dominant coral taxa on Anthropocene reefs, massive Porites. Specifically, we evaluate whether the intensity of parrotfish predation on this key reef-building coral has changed in response to severe coral reef degradation. We found evidence that coral predation rates may have decreased, despite only minor changes in parrotfish abundance. However, higher scar densities on small Porites colonies, compared to large colonies, suggests that the observed decrease in scarring rates may be a reflection of colony-size specific rates of feeding scars. Reduced parrotfish corallivory may reflect the loss of small Porites colonies, or changing foraging opportunities for parrotfishes. The reduction in scar density on massive Porites suggests that the remaining stress-tolerant corals may have passed the vulnerable small colony stage. These results highlight the potential for shifts in ecological functions on ecosystems facing high levels of environmental stress.

L’ecosistema delle scogliere coralline presenta una elevatissima diversità di specie, tuttavia è anche esposto a numerosi disturbi naturali ed antropici. Le minacce includono macro e micro-plastica, riscaldamento globale e predazione. La comprensione delle dinamiche ecologiche della scogliera corallina e le interazioni con attività umane è di primario interesse per evitare la perdita di biodiversità. Questa priorità è fondamentale per aree isolate e remote come la Repubblica delle Maldive, che risulta essere sensibile ai cambiamenti ambientali, anche se è un’area ancora poco investigata. Perciò, questo studio intende esplorare le maggiori minacce e interazioni che causano danni alla scogliera corallina maldiviana. In particolare la corallivoria, per cui, la struttura della popolazione, le preferenze alimentari e le variazioni di densità dei tre corallivori principali delle Maldive (Acanthaster planci, Culcita spp. and Drupella spp.) sono stati studiati. Questi corallivori hanno un ruolo nel deteriorare la copertura di corallo tramite predazione diretta e interazione con altri disturbi di origine antropica come l’aumento delle temperature delle acque. Ciò è specialmente valido per A. planci che ha sviluppato un’esplosione demografica nell’area di studio intensificando la pressione predatoria. Mentre Culcita spp. ha mostrato un ruolo potenzialmente specifico nel rallentare il recupero della scogliera corallina, poiché focalizza la predazione sulle reclute dei coralli. Al contratio, Drupella spp. ha mostrato un collasso della popolazione dopo un evento di mortalità dei coralli, riducendo la pressione predatoria senza apparentemente influenzare la fase di recupero. L’interazione tra corallivoria e minacce di origine antropica intensifica la mortalità dei coralli. Tuttavia non tutti i disturbi antropici sono conosciuti, spesso per mancanza di metodologie standard per quantificarli. Una minaccia aggiuntiva non ancora studiata in dettaglio è rappresentata dai detriti marini antropici (DMA). Perciò, un ulteriore obiettivo è stato quello di sviluppare un metodo efficace e rapido per monitorare e quantificare DMA sulle spiagge usando un drone e un sistema di intelligenza artificiale (IA) basato su un programma di apprendimento artificiale (PlasticFinder). L’alta risoluzione (0.5 cm/pix) dei dati ha permesso di rilevare più dell’ 87% degli oggetti presenti sulla spiaggia rappresentando uno strumento utile a monitorare rapidamente il tasso di accumulo di DMA anche in aree remote ed isolate o disabitate. Negl’ultimi decenni però le scogliere coralline hanno subito una elevata perdita di corallo vivo determinando lo sviluppo di tecniche per il restauro della scogliera corallina. Tuttavia, la valutazione dell’efficacia delle strategie di restauro sono limitate a pochi fattori, come sopravvivenza e crescita del corallo. Il coinvolgimento delle comunità di utenti delle scogliere coralline è stato dimostrato essere fondamentale. L’uso dell’analisi della soddisfazione degli utenti ha rivelato, in questo studio, il bisogno di intervenire con attività di restauro attivo invece che con l’uso di strutture artificiali. Inoltre, donne e locali si sono dimostrati i più interessati a dedicarsi a progetti di restauro, suggerendo che l’investimento nell’addestramento di queste categorie può risultare in una maggiore efficienza delle strategie di restauro. In conclusione, questo lavoro fornisce una visione dettagliata sull’impatto dei principali corallivori alle Maldive. Perciò può rappresentare un utile spunto per futuri studi sull’ecologia dei corallivori, e in più, per la comprensione di ulteriori impatti e strategie per salvaguardare la biodiversità delle scogliere coralline maldiviane.
Coral reef is one of the most diverse ecosystem on Earth, yet one of the most exposed to natural and anthropogenic disturbances. Threats to coral reefs include macro and micro-plastic, global warming and natural coral predators. In this context, understanding the dynamics of coral reef and the interactions with anthropogenic activities is of primary interest to prevent the loss of the reef biodiversity. Such priority is fundamental for isolated and remote areas, such as the Republic of Maldives, which is highly sensitive to changes in environmental conditions, yet, barely investigated. Thus, this study is intended to explore natural and anthropogenic threats recently impacting the maldivian coral reef. Specifically, we investigated the population structure, feeding preferences, distribution and density variation of the three major corallivores occurring in the Maldives (Acanthaster planci, Culcita spp. and Drupella spp.). The results highlighted the role of corallivores in decreasing coral cover by direct predation and co-occurence with temperature-induced coral mortality. Especially for A. planci which showed a severe outbreak in the study area. While Culcita spp. showed a more specific possible role in delaying coral recovery, since resulted to focus predatory pressure on coral recruits. On the other hand, Drupella spp. showed a population collapse compared to previous studies in Maldives, reducing the predatory pressure during the recovery phase of the reef. Thus, the interaction between corallivores and anthropogenic disturbances intesify mortality of corals. Yet, not all disturbances are known, often for lacking of standard methodology for quantification. Among those, a further disturb not known in details is represented by marine anthropogenic debris (AMD). The purpose here was to develop an effective and time-saving method to monitoring and automatically quantifying AMD, using a commercial Unmanned Aerial Vehicle (UAV) and Artificial Intelligence (AI) with a deep-learning based software (PlasticFinder). The high resolution (0.5 cm/pix) of the data allowed to detect more than 87% of the object on the shores and the analysis from PlasticFinder reached a Positive Predictive Value of 94%, which overcame the limits highlighted in the previous AI algorithm used in the literature. The use of drone resulted in a time saving tool to survey AMD accumulation even in remote areas such as uninhabited islands. The degradation of the maldivian coral reef caused by anthropogenic and natural disturbances is a trigger for active strategies to enhance recovery through coral restoration. However, assessment tools of restoration effectiveness and development are still restricted to few ecological factors, such as coral survival and growth. Very few studies included other factors such as socio-economic assessment. The involvement of the community of users of the coral reefs are as important as factors related directly to corals, since users’ satisfaction may drive allocation of private funding useful to improve restoration success. Results presented here, revealed weak points and ways to improve coral restoration programs management in two resorts in the Maldives. The use of satisfaction analysis revealed the need for intervention dedicated to active restoration rather than using artificial reef. Further, women and Maldivians resulted to be the most willing to dedicate themselves to coral restoration project. Thus, suggesting that training session by the resort may be organized for such categories to build team of volunteers for improving local restoration programs. In conclusion, this work provide a detailed overview of the impacts of the main corallivores on the maldivian coral reef. Therefore, it may represent a baseline for future research on the ecology of coral predators and, additionally, for the understanding of further anthropogenic disturbances and for improving strategies to prevent the loss of maldivian coral reef biodiversity.

The Janzen-Connell hypothesis proposes that species-specific enemies promote species coexistence through distance- and density-dependent survival of offspring near conspecific adults. I tested this hypothesis experimentally by transplanting juvenile-sized fragments of two species of brooding corals varying distances from conspecific adults, and observationally by assessing the spatial distribution of those two species in the field. Small fragments (as proxies for ?6 month old juveniles) of Pocillopora damicornis and Seriatopora hystrix were transplanted 3, 12, 24 and 182 cm upstream and downstream (relative to the prevailing current) of conspecific adults and their survivorship and condition (bitten off, overgrown by algae, or bleached) checked every 1-2 d. I also characterized the spatial distribution of P. damicornis and S. hystrix within replicated plots on three Fijian reef flats and measured densities of small colonies within 2 m of larger colonies of each species. Contrary to the Janzen-Connell hypothesis, juvenile-sized transplants exhibited no differences in survivorship as a function of distance from adult P. damicornis or S. hystrix and P. damicornis and S. hystrix were aggregated rather than overdispersed on natural reefs. Survival unaffected by distance from focal colonies as well as certain recruitment processes could generate the observed aggregation. I did observe predation of P. damicornis that was spatially patchy and temporally persistent due to feeding by the territorial triggerfish Balistapus undulatus. This patchy predation did not occur for S. hystrix. Thus, I found no support for the Janzen-Connell hypothesis, but did document hot-spots of species-specific corallivory that could create variable selective regimes on an otherwise more uniform environment, and help maintain the high diversity of corals typical of Indo-Pacific reefs.

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.

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.

Coral reefs around the world are threatened by a variety of sources, from localized impacts, including overfishing and coastal development, to global temperature increases and ocean acidification. Conserving these marine biodiversity havens requires both global and local action informed by scientific research. In this thesis, I use data collected from the coral reefs around Kiritimati atoll (Republic of Kiribati) in the central equatorial Pacific, first to assess the applicability of two common metrics used in passive underwater acoustic research, and second to examine the effects of a marine heatwave and local human disturbance on an assemblage of corallivorous fish. Using acoustic data recorded in 2017 and 2018 on reefs around Kiritimati, I assess how sound pressure level (SPL) and the acoustic complexity index (ACI) respond to changes in fish sounds in a low frequency band (160 Hz – 1 kHz) and snapping shrimp snaps in a high frequency band (1 kHz – 22 kHz). I found that while SPL was positively correlated with increases in fish sounds and snap density, changes in ACI were dependent upon the settings chosen for its calculation, with the density of snaps negatively correlated with ACI across all settings. These findings provide evidence that despite its quick and prolific adoption, acoustic metrics like ACI should be thoroughly field-tested and standardized before they are applied to new ecosystems like coral reefs. Next, using underwater visual censuses (UVCs) of reef fish assemblages, I quantified how two functional groups of corallivores, obligate and facultative, responded to a mass coral mortality event created by the 2015-2016 El Niño. Declines in abundance of both groups were largely driven by the response of coral-associated damselfishes, Plectroglyphidodon johnstonianus in the obligate group and Plectroglyphidodon dickii in the facultative group, to heat stress and subsequent coral mortality. I also observed a significant decline in the species richness of obligate corallivores, and a continued decline in the abundance of obligate corallivores three years after the mass coral mortality event. Additionally, facultative corallivore abundance increased with disturbance, although the effect was modulated by year, likely due to their more adaptable diets. Corallivore assemblage structure was also influenced by the heat stress event, recovery, and local human disturbance. These results detail how an entire corallivorous assemblage is impacted by a coral mortality event and incidentally provide a timeline for corallivore decline. Together, these results provide information about new ways of monitoring coral reefs, and the ways in which two components of the reef fish community, obligate and facultative corallivores, respond to a mass coral mortality event.
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