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Uma nova metodologia para a medida não intrusiva da fração volumétrica e da área interfacial é proposta neste trabalho, com base em redes neurais para processar respostas obtidas de sinais acústicos. A distribuição geométrica das fases dentro do escoamento é mapeada pela velocidade local de propagação acústica, considerada na equação diferencial que governa o problema. Esta equação é resolvida numericamente pelo método de diferenças finitas com as condições de contorno reproduzindo a estratégia de pulso/eco. Um número significativo de distribuições das velocidades de propagação foi considerado na solução da equação diferencial para construir uma base de dados, da qual os parâmetros da rede podem ser ajustados. Especificamente, o modelo neural é construído para mapear características extraídas dos sinais obtidos de quatro sensores acústicos, localizados no contorno externo do domínio de sensoriamento, estimando a fração volumétrica e a área interfacial correspondentes. Estas características correspondem às amplitudes e aos tempos de chegada dos três maiores picos da onda acústica. Os resultados numéricos mostram que o modelo neural pode ser treinado em um tempo computacional razoável e é capaz de estimar os valores da fração volumétrica e da área interfacial dos exemplos do conjunto de teste. / A new methodology for measuring the volumetric fraction and interfacial area in two-phase flows is proposed in this work, based on neural network for processing the responses obtained from an acoustic interrogation signal. The geometrical distribution of the phases within the flow is mapped by the local acoustic propagation velocity which is considered in the governing differential equation. This equation is solved numerically by the finite difference method with boundary conditions reproducing the pulse/echo strategy. A significant number of propagation velocities distributions were considered in the solution of the differential equation in order to construct a database from which the neural model parameters could be adjusted. Specifically, the neural model is constructed to map the features extracted from the signals delivered by four acoustic sensors, placed on the external boundary of the sensing domain, into the corresponding volumetric fraction and interfacial area. These features correspond to the amplitudes and the times of arrival on the three first peaks of the acoustic wave. Numerical results showed that the neural model can be trained in a reasonable computational time and it is capable of estimating the values of the volumetric fraction and the interfacial area of examples of the set of test.

De nombreux prédateurs marins se nourrissent directement des prises des pêcheurs. Ces interactions, définies comme de la déprédation, engendrent des conséquences socio-économiques considérables pour les pêcheurs ainsi que des implications de conservation pour la faune sauvage. D’un côté, la déprédation endommage le matériel et augmente l’effort de pêche pour atteindre les quotas. D’un autre côté, la déprédation augmente le risque de mortalité des prédateurs marins (prise accidentelle ou rétorsion létale par les pécheurs). La pêcherie à la palangre est la plus impactée par la déprédation, principalement par les odontocètes, ce qui incite à trouver des solutions. La majorité des études se concentrant sur la déprédation s’est principalement basée sur des observations en surface, de ce fait la manière dont les prédateurs retirent les poissons sur les lignes reste confuse. Par ailleurs, l’impact de la déprédation sur le comportement des pêcheurs ainsi que les facteurs expliquant leur détectabilité n’ont reçu que peu d’intérêt. L’objectif de cette thèse est donc d’étudier ces problématiques par un suivi acoustique, une utilisation de balises et une approche en écologie comportementale humaine, en se concentrant sur la pêcherie palangrière française ciblant la légine australe (Dissostichus eleginoides) impactée par la déprédation des orques (Orcinus orca) et des cachalots (Physeter macrocephalus). Les capitaines ont été décrits comme recherchant leur ressource selon la théorie de « l’optimal foraging », mais avec des perceptions de la compétition et du succès de pêche qui divergent. Certains capitaines seraient ainsi plus enclins à remonter les palangres au plus proche et à rester sur une zone, même en présence de compétition, augmentant alors le risque d’interaction. L’acoustique des navires a révélé que certaines manoeuvres (marche arrière par exemple) propagent différemment sous l’eau. La manière dont les capitaines manoeuvrent leur palangrier influencerait ainsi leur détectabilité et donc leur risque d’interaction avec les prédateurs. D’autre part, l’utilisation de capteurs sur les palangres et les animaux a révélé que les orques et les cachalots sont capables de déprédater sur les palangres posées sur le fond marin. Ces observations laissent à penser que les odontocètes sont en mesure de localiser l’activité de pêche bien avant la remontée de la ligne, ce qui pourrait être expliqué par une signature acoustique spécifique du déploiement de la ligne. L’ensemble des résultats de cette thèse suggère que la déprédation sur les palangres démersales est très probablement sous-estimée. Cette thèse apporte également des éléments importants pour la lutte contre la déprédation, en montrant la nécessité de protéger les palangres dans l’intégralité du processus de pêche. / Many marine predator species feed on fish caught by fishers directly from the fishing gear. Known as depredation this interaction issue has substantial socio-economic consequences for fishermen and conservation implications for the wildlife. Costs for fishers include damages to the fishing gear and increased fishing effort to complete quotas. For marine predators, depredation increases risks of mortality (lethal retaliation from fishers or bycatch on the gear). Longline fisheries are the most impacted worldwide, primarily by odontocetes (toothed whales) depredation, urging the need for mitigation solutions to be developed. Most of studies assessing depredation have primarily relied on surface observation data, thus the way odontocetes interact with longlines underwater remains unclear. Besides, the way fishermen respond to depredation during fishing operations, or can influence their detectability to odontocetes, have been poorly investigated. This thesis therefore aimed at investigating these aspects through a passive acoustic monitoring, bio-logging and human ecology approaches, focusing on the French Patagonian toothfish (Dissostichus eleginoides) longline fisheries impacted by killer whales (Orcinus orca) and sperm whales (Physeter macrocephalus). Firstly, this thesis reveals that captains behave as optimal foragers but with different personal perception of competition and fishing fulfilment. Some captains would thus be more likely to stay within a patch or to haul closest longline even in presence of competition, suggesting these captains would show higher interaction rates. Additionally, the propagation of vessels’ acoustics varied depending on the type of manoeuvre (e.g. going backward vs. forward). The way captains use their vessels to navigate may therefore influence their detectability and so their depredation level. Secondly, loggers deployed on both the longlines (accelerometers) and odontocetes (GPS-TDR) revealed that killer whales and sperm whales are able to depredate on longlines while soaking on the seafloor. These observations suggest, therefore, that odontocetes can localise fishing activity before the hauling, which could be partially explained by specific acoustic signatures recorded during the setting process. Altogether, the results of the thesis suggest that depredation rates on demersal longlines are most likely underestimated. The thesis also brings some important insights for mitigation measures, suggesting that countermeasures should start from setting to hauling.

The Littoral Acoustic Demonstration Center has collected passive acoustic monitoring data in the northern Gulf of Mexico since 2001. Recordings were made in 2007 near the Deepwater Horizon oil spill that provide a baseline for an extensive study of regional marine mammal populations in response to the disaster. Animal density estimates can be derived from detections of echolocation signals in the acoustic data. Beaked whales are of particular interest as they remain one of the least understood groups of marine mammals, and relatively few abundance estimates exist. Efficient methods for classifying detected echolocation transients are essential for mining long-term passive acoustic data. In this study, three data clustering routines using k-means, self-organizing maps, and spectral clustering were tested with various features of detected echolocation transients. Several methods effectively isolated the echolocation signals of regional beaked whales at the species level. Feedforward neural network classifiers were also evaluated, and performed with high accuracy under various noise conditions. The waveform fractal dimension was tested as a feature for marine biosonar classification and improved the accuracy of the classifiers. [This research was made possible by a grant from The Gulf of Mexico Research Initiative. Data are publicly available through the Gulf of Mexico Research Initiative Information & Data Cooperative (GRIIDC) at https://data.gulfresearchinitiative.org.] [DOIs: 10.7266/N7W094CG, 10.7266/N7QF8R9K]

In conservation ecology, abundance estimates are an important factor from which management decisions are based. Methods to estimate abundance of cetaceans from visual detections are largely developed, whereas parallel methods based on passive acoustic detections are still in their infancy. To estimate the abundance of cetacean species using acoustic detection data, it is first necessary to correctly identify the species that are detected. The current automatic PAMGUARD Whistle Classifier used to automatically identify whistle detection of cetacean species is modified with the objective to facilitate the use of these detections to estimate cetacean abundance. Given the variability of cetacean sounds within and between species, developing an automated species classifier with a 100% correct classification probability for any species is unfeasible. However, through the examples of two case studies it is shown that large and high quality datasets with which to develop these automatic classifiers increase the probability of creating reliable classifiers with low and precise misclassification probability. Given that misclassification is unavoidable, it is necessary to consider the effect of misclassified detections on the number of observed acoustic calls detected and thus on abundance estimates, and to develop robust methods to cope with these misclassifications. Through both heuristic and Bayesian approaches it is demonstrated that if misclassification probabilities are known or estimated precisely, it is possible to estimate the true number of detected calls accurately and precisely. However, misclassification and uncertainty increase the variance of the estimates. If the true numbers of detections from different species are similar, then a small amount of misclassification between species and a small amount of uncertainty in the probabilities of misclassification does not have a detrimental effect on the overall variance and bias of the estimate. However, if there is a difference in the encounter rate between species calls associated with a large amount of uncertainty in the probabilities of misclassification, then the variance of the estimates becomes larger and the bias increases; this in return increases the variance and the bias of the final abundance estimate. This study despite not bringing perfect results highlights for the first time the importance of dealing with the problem of species misclassification for cetacean if acoustic detections are to be used to estimate abundance of cetaceans.

Le milieu marin est insonifié par une grand variété de sources acoustiques, qui peuventêtre monitorées par des enregistreurs acoustiques passifs autonomes. Parmi les sons enregistrés, ontrouve un grand nombre de signaux transitoires (signaux éphémères de durée courte), auxquelsappartiennent notamment les signaux impulsionnels que nous étudions dans cette thèse. Les signauximpulsionnels ont des propriétés spécifiques, telles que leur durée très courte (<1ms), leur faiblenombre d’oscillations, leur forte directivité, qui les rendent difficiles à étudier avec les outils detraitement du signal traditionnels (transformée de Fourier, autocorrélation, etc.).Dans un premier temps, nous nous intéressons à la détection des sources qui émettent des sériesd’impulsions rythmées (dauphins, cachalots, bélugas). Cette détection, s’appuie uniquement surles temps d’arrivée des impulsions reçues, pour effectuer une analyse du rythme au moyen d’uneautocorrélation complexe, et construire une représentation temps-rythme, permettant : i) de détecterles rythmes, ii) de connaître les temps de début et fin des émissions rythmées, iii) de connaître lavaleur du rythme et son évolution.Dans un second temps, nous étudions le potentiel d’une technique appelée analyse par récurrence desphases, pour caractériser les formes d’onde des impulsions. Après avoir présenté le cadre général decette méthode d’analyse, nous l’utilisons dans trois chaînes de traitement répondant à chacune destâches suivantes : i) détection des transitoires, ii) caractérisation et reconnaissance des transitoires,iii) estimation des différences des temps d’arrivée des transitoires sur deux capteurs.Toutes les méthodes développées dans cette étude ont été testées et validées sur des données simuléeset sur des données réelles acquises en mer / The underwater environment is insonified by a wide variety of acoustic sourcesthat can be monitored by autonomous passive acoustic recorders. A large number of the recordedsounds are transient signals (short-finite duration signals), among which the pulse signals that westudy in this thesis. Pulse signals have specific properties, such as a very short duration (<1ms), fewoscillations, a high directivity, which make them difficult to study by classical signal processing tools(Fourier transform, autocorrelation).In the first part of this study, we develop a method to detect sound sources emitting rhythmic pulsetrains (dolphins, sperm whales, beluga whales). This detector uses only the time of arrival of pulses atthe hydrophone to perform a rhythm analysis based on a complex autocorrelation and a time-rhythmrepresentation. This allows : i) to detect rhythmic pulse trains, ii) to know the beginning and endingtimes of pulse trains, iii) to know the value of the rhythm.In the second part of this thesis, we study the potential of a method called Recurrence Plot Analysis tocharacterize waveforms of pulse signals. After a general presentation of this method we develop threesignal processing architectures based on it, to perform the following tasks : i) transient detection, ii)transient characterization and pattern recognition, iii) estimation of time difference of arrival of thetransient on two hydrophones.All the methods developped in this thesis are validated on simulated and real data recorded at sea.

Submitted by Marcio Emanuel Paixão Santos (marcio.santos@ucsal.br) on 2018-05-04T20:56:14Z No. of bitstreams: 2 DISSERTACAOFRANCISCOGUIMARAES.docx: 2450268 bytes, checksum: bae026f7f497d1377ce648b34ca273b6 (MD5) DISSERTACAOFRANCISCOGUIMARAES.pdf: 1513020 bytes, checksum: 5e830a7d625f9e4969048192a6f90e85 (MD5) / Approved for entry into archive by Rosemary Magalhães (rosemary.magalhaes@ucsal.br) on 2018-05-08T14:30:15Z (GMT) No. of bitstreams: 2 DISSERTACAOFRANCISCOGUIMARAES.docx: 2450268 bytes, checksum: bae026f7f497d1377ce648b34ca273b6 (MD5) DISSERTACAOFRANCISCOGUIMARAES.pdf: 1513020 bytes, checksum: 5e830a7d625f9e4969048192a6f90e85 (MD5) / Made available in DSpace on 2018-05-08T14:30:15Z (GMT). No. of bitstreams: 2 DISSERTACAOFRANCISCOGUIMARAES.docx: 2450268 bytes, checksum: bae026f7f497d1377ce648b34ca273b6 (MD5) DISSERTACAOFRANCISCOGUIMARAES.pdf: 1513020 bytes, checksum: 5e830a7d625f9e4969048192a6f90e85 (MD5) Previous issue date: 2017-12-21 / A poluição sonora é um problema cada vez mais evidente no cotidiano das grandes cidades no mundo moderno, e o efeito desse ruído antrópico em áreas naturais e urbanas tem sido alvo de inúmeras investigações. O estudo da paisagem sonora vem se tornando uma ferramenta importante para o entendimento da dinâmica acústica ambiental. A determinação do efeito da paisagem sonora sobre a detectabilidade acústica de anuros na região metropolitana de Salvador-BA, identificando e analisando os componentes acústico da paisagem, através de gravações de áudio automatizadas. 14 anuros em atividade acústica foram identificados em duas estações distintas, seca e chuvosa. O Escalonamento multidimensional não métrico (NMS) demostrou como os componentes da paisagem sonora se organizam e relacionam com as espécies de anuros identificadas nas gravações. Nessa análise podemos observar a relação de algumas espécies de anuros com a covariante decibel (dBA), testamos modelos de detectabilidade a partir dessa variável ambiental e encontramos valores bem distintas, Pseudopaludicola mystacalis apresentou maior detectabilidade entre os anuros estudados (p = 100%), seguido do Scinax auratus (89,6%) e Leptodactylus vastus (p= 70,83%). O efeito da paisagem sonora nos anuros foi diferente para cada espécie estudada, enquanto o P.mystacalis parece não se incomodar com o nível de ruído das localidades o L. vastus mudanças comportamentais em ambiente mais ruidoso. Os estudos de Paisagens Sonoras são registros permanentes de acontecimentos de uma determinada localidade, numa determinada época. O que torna as gravações desse trabalho ferramentas importantes para analises futuras dessas duas áreas de estudos.

Uma nova metodologia para a medida não intrusiva da fração volumétrica e da área interfacial é proposta neste trabalho, com base em redes neurais para processar respostas obtidas de sinais acústicos. A distribuição geométrica das fases dentro do escoamento é mapeada pela velocidade local de propagação acústica, considerada na equação diferencial que governa o problema. Esta equação é resolvida numericamente pelo método de diferenças finitas com as condições de contorno reproduzindo a estratégia de pulso/eco. Um número significativo de distribuições das velocidades de propagação foi considerado na solução da equação diferencial para construir uma base de dados, da qual os parâmetros da rede podem ser ajustados. Especificamente, o modelo neural é construído para mapear características extraídas dos sinais obtidos de quatro sensores acústicos, localizados no contorno externo do domínio de sensoriamento, estimando a fração volumétrica e a área interfacial correspondentes. Estas características correspondem às amplitudes e aos tempos de chegada dos três maiores picos da onda acústica. Os resultados numéricos mostram que o modelo neural pode ser treinado em um tempo computacional razoável e é capaz de estimar os valores da fração volumétrica e da área interfacial dos exemplos do conjunto de teste. / A new methodology for measuring the volumetric fraction and interfacial area in two-phase flows is proposed in this work, based on neural network for processing the responses obtained from an acoustic interrogation signal. The geometrical distribution of the phases within the flow is mapped by the local acoustic propagation velocity which is considered in the governing differential equation. This equation is solved numerically by the finite difference method with boundary conditions reproducing the pulse/echo strategy. A significant number of propagation velocities distributions were considered in the solution of the differential equation in order to construct a database from which the neural model parameters could be adjusted. Specifically, the neural model is constructed to map the features extracted from the signals delivered by four acoustic sensors, placed on the external boundary of the sensing domain, into the corresponding volumetric fraction and interfacial area. These features correspond to the amplitudes and the times of arrival on the three first peaks of the acoustic wave. Numerical results showed that the neural model can be trained in a reasonable computational time and it is capable of estimating the values of the volumetric fraction and the interfacial area of examples of the set of test.

L’aménagement du territoire et l’intensification agricole constituent deux causes majeures du déclin de la biodiversité. La plupart des projets d’aménagement sont tenus d’appliquer la séquence « éviter-réduire-compenser » (ERC) aux impacts générés, pour atteindre une absence de perte nette de biodiversité. La mise en place de cette séquence dans le cas de la construction de parcs éoliens se heurte à la difficulté d’évaluation et de prédiction des impacts dont la mortalité par collisions avec les chiroptères et l’avifaune. Nous avons en effet montré dans un travail préliminaire que les manques théoriques sur l’évaluation de l’impact combinés à une qualité variable des études réglementaires amènent aujourd’hui à i) un évitement et une réduction peu efficaces, ii) une compensation la plupart du temps inexistante ou hasardeuse. Face aux contraintes d'implantation, les éoliennes sont principalement installées en milieu agricole. Ce dernier, en plus de constituer un espace de production alimentaire, de support d’énergie renouvelable et de biodiversité, doit également assurer le rôle de compensation des impacts générés par la production d’énergie éolienne. Il apparaît d’autant plus urgent d’étudier cette problématique que ces impacts semblent pouvoir affecter les populations d’espèces en fort déclin. Dans un premier temps, nous avons quantifié un deuxième type d’impact des éoliennes, la répulsion exercée sur les chiroptères, jusqu’ici largement méconnue et de ce fait non pris en compte dans les projets d’implantation. Nous mettons en évidence un fort impact négatif de la présence d’éoliennes sur la fréquentation des haies par les chiroptères jusqu’à une distance minimale de 1000 m autour de l’éolienne, engendrant ainsi d’importantes pertes d’habitats. Or, à l’échelle du nord-ouest de la France, 89% des éoliennes sont implantées à moins de 200 m d’une lisière arborée (haie ou forêt), cette distance constituant une recommandation européenne. Cette étude améliore donc les connaissances liées à l’implantation des éoliennes pour optimiser l’évitement d’une partie des impacts, les rendant compensables par leur quantification. Nous avons ensuite comparé différentes mesures couramment utilisées en compensation (jachères et infrastructures agroécologiques), en développant un calcul d’équivalence multi-taxonomique entre ces mesures. Ceci a permis en toute transparence de proposer des alternatives aussi efficaces à une mesure peu acceptable (par exemple les jachères en contexte grandes cultures), maximisant les leviers de mise en place de la compensation. Enfin, nous avons évalué la faisabilité de mesures compensatoires potentiellement plus acceptables, non plus axées sur l’ajout d’éléments dans la matrice agricole, mais sur des mesures visant directement la qualité de cette matrice support de biodiversité. En se focalisant sur des changements de pratiques agricoles n’engendrant pas ou peu de pertes de rendement, nous montrons que la simplification du travail du sol peut apporter de forts bénéfices à l’avifaune et aux chiroptères. Toutefois, ce bénéfice peut fortement varier en fonction des pratiques visant à limiter l’excès de végétation spontanée généré par l’absence de labour. Une diminution du travail du sol et de l’usage d’herbicides peuvent créer des gains comparables à ceux obtenus en agriculture biologique. La thèse souligne l’urgence de reconsidérer les stratégies actuelles d’implantation et d’exploitation des éoliennes en milieu agricole, causant de fortes pertes d’habitats et une mortalité systématique. Elle montre aussi qu'en dépit des manques de connaissances limitant les possibilités d’un dimensionnement des mesures compensatoires fondé sur une quantification intégrale des impacts, nous sommes en mesure d’apporter d’ores et déjà des gains écologiques efficaces en milieu agricole grâce à des mesures acceptables par l’ensemble des acteurs. / Land-use planning and agricultural intensification are two major causes of biodiversity loss. Most of development projects have to apply the mitigation hierarchy, i.e. avoid, reduce then offset impacts on biodiversity, in order to achieve the no net loss. Wind farm installation makes the mitigation hierarchy application difficult due to the lack of knowledges regarding the quantification and the prediction of impacts, characterized by collisions of birds and bats with turbines. In a preliminary study we showed that the current fail of impact assessment studies in i) the avoidance and the reduction as well as ii) the offsetting of impact, are mainly linked to a lack of theoretical knowledges and a low quality of studies. Installation constraints often imply to implement wind turbines in farmland areas. Such areas have the triple function of food production, renewable energy and biodiversity carrier, but they also have to offset impacts on biodiversity, which are generated by wind turbines. Thus, there is an urgent need to improve the consideration of impacts on biodiversity in projects, which would have underestimated effects on populations. In a first time, we quantified a new type of impact: the wind turbine revulsion on bats. This impact is so far little known and not taken into account in assessment studies for wind farm installations. We highlighted a negative long distance impact (over 1000 m) of wind turbine proximity on bat activity at hedgerows, which is a highly attractive habitat for this taxa. These strong negative impacts currently lead to high losses of habitat use. Moreover, at the region scale study (north-west France), 89% of turbines are implemented at less than the European recommendations (200 m to wooded edges -hedgerows or forests). Thus, this study improved knowledges in order to optimize avoidance of this impact and made them measurable allowing their offsetting. We then compared different commonly used offsetting measures (i.e. fallows and agroecological elements), by developing a method for calculating ecological equivalences between offset measure. This allowed in complete transparency to find alternative measures as efficiently as an initial low acceptable measure (i.e. fallows in open field area). Such a method allowed an effective implementation of measures. Finally, we assessed the ecological gain provided by new types of measures such as changes in farming practices. Unlike classic measures which are usually an implementation of new elements in the landscape, changes in farming practices consist in quality improving of arable land features. Because we studied changes which do not implies losses of yield, or low in first years after changes, such measures are potentially more acceptable for farmers. We showed that tillage and herbicide reduction could positively impact birds and bats. However, to reduce tillage (i.e. no ploughing) implies to adapt the method to control weeds, previously performed by ploughing. Several possibilities can be used such as cover cropping or herbicide use intensification. In this context, our results also highlighted that positive impacts could vary significantly among underlying weed control possibilities. For instance, tillage reduction, when one herbicide pass is removed, generates as much ecological gain than organic farming system. This PhD thesis highlights the urgent need to adapt wind energy planning and these exploitation in farming areas, due to high habitat loss and systematic mortality. This thesis also shows that despite the current lack of knowledges, preventing to design offsetting measures facing to quantified impacts, implementation of acceptable measures for stakeholders may provide effective gains for bats and birds.

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. / Graduate / 2022-01-15