Coral recruitment is a key process that contributes to the community structure and resilience of coral reefs. As such, quantification of this process is important to assist with the management of these threatened ecosystems. While coral recruitment has been the focus of numerous studies over the past 30 years, an understanding of this process on the high-latitude reefs of South Africa is limited. In addition, variations in methods used in recruitment studies make the results difficult to compare. A rapid in-situ method for universal application in the detection of early post-settled recruits would thus be useful. In this study, scleractinian coral recruitment was investigated at three study sites on Two-mile Reef, over two six-month sampling periods, covering summer and winter. Two components were investigated by attaching settlement tiles consisting of ceramic and marble tiles, and ceramic tiles conditioned with crustose coralline algae (CCA) onto the reef in a spatially structured experimental design. Firstly, coral recruitment was compared on the three different tile surfaces and fluorescence photography was investigated as a rapid in situ technique to detect early post-settled recruits. Fluorescence photography was then used to compare recruitment on tiles with the surrounding natural substrata. Secondly, the spatial and temporal variation in the abundance, composition and size of recruits was investigated. Additionally, the percentage cover of biota surrounding each recruit within three millimeters of its corallum was visually estimated to quantify the microhabitat surroundings of coral recruits. Overall recruitment on the three tile types differed, yet spatial variation in coral recruitment, regardless of tile surface, accounted for most of the variance in recruitment. While the highest recruitment occurred on CCA tiles, this was not significantly greater than ceramic tiles, indicating that the conditioning of ceramic tiles with Mesophyllum funafutiense CCA did not enhance coral settlement in this study. Although many recruits were not detected with fluorescent photography (73%), it proved useful to reveal recruits as small as 0.75 mm in corallum diameter, and indicated that recruitment on the tiles and natural substratum differ significantly. Spatially, the abundance and composition of coral recruits differed between study sites, within sites, and predominantly occurred on tile edges. Coral recruitment was lowest at shallower sites, and was dominated by pocilloporids regardless of study site. Additionally, the abundance and composition of recruits differed between the two sampling periods, with a 6.6-fold decrease in the mean abundance of recruits from summer to winter, with only pocilloporid settlement occurring in the latter season. The majority of recruits were <3 mm, and their microhabitat was dominated by bare substrata and crustose coralline algae. The results suggest that, while the choice of artificial settlement surface used in such studies can have a profound influence on the results, spatial variation in recruitment can be greater. The recovery of scleractinian coral taxa on Two-mile Reef in the event of a severe disturbance is expected to differ, with greatest recovery in areas of high levels of recruitment. The microhabitat surrounding recruits is described here for the first time, suggesting that further research into coral-crustose coralline algae interactions is warranted. Finally, while fluorescence photography has its limitations, it shows promise as a useful tool for rapid qualitative, but not quantitative, assessment of recruitment. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2011.

The development of coral reefs is largely restricted to areas within the tropics where favourable conditions for both coral and reef growth prevail. There is, however, a continuum from these typical, accretive reefs in the tropics to marginal, non-accretive, coral-dominated reef communities which occur at higher latitudes. High-latitude reefs function similarly in many regards to their tropical counterparts and are regulated by similar processes to a varying degree. In this study, the major biological and physico-chemical processes were assessed which directly or indirectly prevent the continued persistence of reefal frameworks and thus hinder reef accretion on high-latitude reefs in the iSimangaliso Wetland Park. These reefs have a high diversity of hard and soft corals with significant reef coverage, yet little evidence of any biogenic accretion has been observed. The scleractinian coral, Acropora austera, is one of the few corals which may be responsible for reef framework production. It exhibits a gregarious growth pattern, forming large, monospecific stands with an interlocking framework characteristic of the early stages of reef accretion. The framebuilding potential of A. austera and the continued persistence of such frameworks were thus determined by in situ monitoring of coral growth, mortality, bioerosion and several physico-chemical parameters. Growth rate and mortality of A. austera branches were measured at three sites of differing stand size and apparent age. This was achieved by repeated image analysis and by staining branches with the vital stain, Alizarin Red S. Both measures of growth yielded a similar linear extension rate of 24.5 mm/yr (n = 467), comparable to related species at similar latitudes. Mean branch mortality was as high as 50%, with clear differences manifested between each A. austera stand. Branch extension rates and branch mortality were inversely related between sites. Small, young stands exhibited significantly faster coral growth rates, lower mortality and a net increase in overall branch length over the study period, whilst the opposite was true of larger, more developed stands. In addition, bioerosion was determined at each site to assess its potential for carbonate removal and its destabilizing effect on reef frameworks. Bioerosion intensity was recorded as “percentage area damage” within cross-sections and “frequency of occurrence” of bioeroding organisms in coral rubble fragments (n = 120). The level of bioerosion was found to be substantial (up to 11.5% loss in weight of coral fragments over the 12-month study period) and was found to decrease significantly with a reduction in size of each A. austera stand. Aragonite saturation state is considered a major factor that limits the geographical range of coral reefs globally. Although previously thought to be limiting in Maputaland, mean ΩArag values of 4.40±0.29 were measured on the reefs in summer and 4.33±0.21 in winter and thus would not have limited reef development. Past studies have noted the turbulence on South African east coast reefs and its adverse effect on reef development. This was corroborated in this study with the measurement of considerable sediment re-suspension (0.17 g cm⁻² day⁻¹) and regular damage to both living coral and the reef framework caused by large swells. These results lead to the theory that Acropora austera stands senesce with increasing size and age. Although large coral frameworks are found on the Maputaland reefs, they do not persist in the long term. High rates of sediment re-suspension prevent infilling of the interstitial spaces and eventual cementation, while high levels of bioerosion lead to framework instability over time. Rough seas further hamper accretion by physical removal of both living coral and the coral-derived framework, thus removing recent growth. This process is suspected to cause an imbalance in the carbonate budget of these marginal reefs, ultimately favoring carbonate removal over carbonate deposition. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2011.

Coral communities have begun to form under small inlet-style bridges along the causeway connecting Cayo Coco to Cayo Guillermo. To understand how these bridge-reefs formed and characterize their attributes relative to surrounding communities, a combination of ecological observations and 13C isotopes were analyzed from the bridges and surrounding reefs, mangrove channels and seagrass patches. Hierarchical Cluster Analysis, Detrended Correspondence Analysis and Canonical Correspondence Analysis were carried out to group which physical attributes contributed to the coral communities in the bridge-reefs and also which habitats they were most similar to, with respect to coral and benthic composition. Bridge reef coral assemblages resembled shallow patch reefs and mangrove channels, while benthic coverage was similar to mangrove channels. Organic matter was from combined seagrass and mangrove sources, with mangrove dominating in some regions more than others. This work demonstrates that habitats within the seascape are inter-related through varying mechanisms and development is multi-dimensional.

The 2004 Indian Ocean tsunami created a catastrophic disturbance at several scales along the entire Andaman Sea coast. As the first large-scale tsunami occurring in recent history, this event provided a unique opportunity to use modern instrumentation and in situ observation to study tsunami dynamics and effects on coastal systems. Along Thailand’s coast, consequences of this disturbance were highly variable in space and time, with pronounced changes to certain coral reefs and human communities. This thesis outlines two case study-based research projects designed to gain some understanding of the ecological and social dynamics of the tsunami in Thailand. From a Geographical perspective, responses to this massive disturbance may support an incentive-based direction for marine conservation in Thailand. The first project occurred within Mu Koh Surin Marine National Park, Thailand. Variability in the physical response of fringing hard coral reefs to the tsunami was examined using SCUBA surveys. Patterns in variability were distinct from typical hard coral responses during tropical storms suggesting differences in the nature of these hydrodynamic disturbances. Coral colony morphologies and reef shape mainly did not influence variability in tsunami response; however, unique effects were observed on reef slopes over 45°. There was no detected influence of reef depth. Variability in effects based on the spatial location of reefs was observed: proximity to bathymetrical constrictions accounted for substantial variability, while reef aspect did not. Overall, just over 10% of sampled reef area was affected, with evidence of rapid coral recovery in the form of tissue re-growth and apical skeletal growth within four months of the event at most sites. The second project explored the effects of the tsunami on Phuket’s diving industry. The response of industry members and recreational divers to tsunami effects was examined using interviews and questionnaires as well as observational dives with dive guides and clients on chartered trips during the 2004-5 post-tsunami diving season. A short-term reduction in the number of diving companies and diving tourism in Phuket was observed immediately following the tsunami; this can be attributed to terrestrial damage and trip cancellations. Although there were expectations for high levels of dive site damage, most recreational divers did not perceive any damage on dive sites in 2005 – even while diving on surveyed sites with as much as 76-100% of reef area reportedly affected. This low rate of perception may be partially explained by diving ability, but was more likely due to site variability and variability in tsunami response within dive sites allowing guides to preferentially avoid acutely damaged areas. During the post-tsunami low tourism period, industry members contributed substantial resources to rescue, relief and restoration efforts along Thailand’s Andaman Sea Coast. Industry members also participated in several government and university-led tsunami monitoring and rehabilitation efforts. While measurable changes to Phuket’s diving industry seem to have been short-term, this response of industry members to the event may have increased potential for long-term collaboration with government and universities. Enhanced communication among these parties could facilitate future incentive-driven industry contributions toward marine conservation in Thailand.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Os fatores que explicam a distribuição observada em plantas e animais é uma pergunta que intriga naturalistas, biogeógrafos e ecólogos há mais de um século. Ainda nos primórdios da disciplina de ecologia, as tolerâncias ambientais já haviam sido apontadas como as grandes responsáveis pelo padrão observado da distribuição dos seres vivos, o que mais tarde levou à concepção de nicho ecológico das espécies. Nos últimos anos, o estudo das distribuições dos organismos ganhou grande impulso e destaque na literatura. O motivo foi a maior disponibilidade de catálogos de presença de espécies, o desenvolvimento de bancos de variáveis ambientais de todo o planeta e de ferramentas computacionais capazes de projetar mapas de distribuição potencial de um dado organismo. Estes instrumentos, coletivamente chamados de Modelos de Distribuição de Espécies (MDEs) têm sido desde então amplamente utilizados em estudos de diferentes escopos. Um deles é a avaliação de potenciais áreas suscetíveis à invasão de organismos exóticos. Este estudo tem, portanto, o objetivo de compreender, através de MDEs, os fatores subjacentes à distribuição de duas espécies de corais escleractíneos invasores nativos do Oceano Pacífico e ambas invasoras bem sucedidas de diversas partes do Oceano Atlântico, destacadamente o litoral fluminense. Os resultados mostraram que os modelos preditivos da espécie Tubastraea coccinea (LESSON, 1829), cosmopolita amplamente difundida na sua região nativa pelo Indo- Pacífico demonstraram de maneira satisfatória suas áreas de distribuição nas áreas invadidas do Atlântico. Sua distribuição está basicamente associada a regiões com alta disponibilidade de calcita e baixa produtividade fitoplanctônica. Por outro lado, a aplicação de MDEs foi incapaz de predizer a distribuição de T. tagusensis (WELLS,1982) no Atlântico. Essta espécie, ao contrário de sua congênere, tem distribuição bastante restrita em sua região nativa, o arquipélago de Galápagos. Através de análises posteriores foi possível constatar a mudança no nicho observado durante o processo de invasão. Finalmente, o sucesso preditivo para T. coccinea e o fracasso dos modelos para T. tagusensis levantam importantes questões sobre quais os aspectos ecológicos das espécies são mais favoráveis à aplicação de MDEs. Adicionalmente, lança importantes ressalvas na utilização recentemente tão difundida destas ferramentas como forma de previsão de invasões biológicas e em estudos de efeitos de alterações climáticas sobre a distribuição das espécies. / The factors underpinning the observed distribution of plants and animals across time and space are a central question in ecology and has intrigued scientists for over a century. But even back on those early times, the role of climatic tolerances of the species were recognized as one of the main explanations for such distributional patterns. Later, these assumptions gave rise to the concept of niche which triggered several advances in the study of natural history. Recently, these studies were addressed in the light of novel computational techniques capable of providing potential distributional maps for a given species, generically called Species Distribution Models (SDMs). This coupled with the broader availability of species occurrence records and of environmental data from international databases made studies with SDMs very popular and ubiquitous in the literature. One of the main uses of the SDMs approach is the assessment of potentially susceptible areas of invasion by non- indigenous species. Therefore, here we used SDMs to better understand the major factors related to the current distribution of two well established invasive scleractinian coral species in the Atlantic, both from the Pacific Ocean. The results showed that the models were successful in predicting the potentially invaded sites by the cosmopolitan Tubastraea coccinea (LESSON, 1829), broadly distributed throughout the Pacific. This species distribution was basically associated with increasing concentrations of calcite and lower levels of phytoplankton activity. However, the models were incapable of predicting the survival and establishment of T. tagusensis (WELLS, 1982) in the Atlantic. This species, unlike its congener, has a very restricted distribution in its native regions, the Galapagos Islands. A posterior analyzes indeed showed a niche shift during the invasion event of T. tagusensis in the Atlantic. Finally, the good modelling results for T. coccinea contrasted with the failure of modelling T. tagusensis invasion highlight important explanations on methodological procedures in SDMs. It also helps to better understand which ecological aspects of the species are favourable toward good modelling performance. In addition to that, these results calls for precaution when analyzing SDMs results, particularly in invasion and climate change scenarios studies.

O recrutamento é extremamente importante no ambiente recifal, sendo o principal responsável pelo reabastecimento de populações adultas de peixes. Esse fenômeno é altamente complexo, não sendo claro se é influenciado apenas por processos estocásticos ou também por processos determinísticos. No presente estudo avaliamos a dinâmica temporal do recrutamento de diversas espécies de peixes recifais, identificando sítios de berçário (i.e. recrutamento estável e alto) e a influência de variáveis ambientais. Para tal, utilizamos dados de um monitoramento de médio prazo (i.e. 2001 a 2014) realizado no Banco dos Abrolhos (BA-Brasil). Foram amostrados mais de 45 sítios, sendo levantados dados sobre a comunidade de peixes, comunidade bentônica e outras variáveis ambientais. A partir desses dados, avaliamos a variação do recrutamento por sítio em dois períodos distintos (i.e. 2001-2008/2006-2014) e a influência de variáveis ambientais no recrutamento, através da técnica Boosted Regression Trees. Constatamos que diversas espécies de peixe apresentam-se com recrutamento estável em distintos sítios de amostragem. Também observamos um efeito positivo da densidade de peixes recifais coespecíficos adultos e da cobertura relativa de algas frondosas no recrutamento de diversas espécies analisadas. No geral, observamos que há certa espécie especificidade no processo de recrutamento, porém, em escalas espaciais maiores, os padrões podem estar ligados a características mais gerais, relacionadas a um grupo taxonômico mais elevado. Em relação aos sítios de berçário, um se destacou, sendo berçário de 5 diferentes espécies, incluindo Scarus trispinosus, uma das espécies prioritárias para conservação na região de Abrolhos. Assim, recomendamos a criação de uma área marinha de proteção integral que englobe o sítio em questão. Além disso, as descobertas deste trabalho nos permitem reforçar a teoria de que o recrutamento de peixes recifais pode ser influenciado por fenômenos determinísticos e não varia simplesmente de maneira estocástica. / Recruitment is extremely important in the reef environment, because it is the main source of population replenishment. Reef fish recruitment is a highly complex process and it is not clear whether it is influenced only by stochastic processes or also by deterministic processes. Herein, we aimed to investigate temporal dynamics of reef fish recruitment, identify nursery sites (i.e. predictably high recruitment sites) and evaluate the influence of environmental variables on recruitment. We used data from a medium-term time series (i.e. 2001-2014) of scientific surveys in Abrolhos Bank (BA-Brazil). We sampled more than 45 sites, for several consecutive years and recorded data about fish community, benthic community and other environmental variables. We assessed the variation of recruitment on each site, during two distinct periods (i.e. 2001-2008 / 2006-2014), and used the Boosted Regression Trees technique to evaluate the influence of environmental variables in recruitment. We found that several reef fish species present a low variable recruitment at different sampling sites. BRT showed a positive effect of the coverage of flesh algae and abundance of conspecific in the abundance of recruits (i.e. young-of-year) of many species. Overall, we notice that the recruitment traits seems to be species specific, but we also found indications that in larger spatial scales, recruitment spatial and temporal patterns may be related to general characteristics among species of the higher taxa. Nursery sites varied among species and one site was a nursery to 5 different reef fish species, including Scarus trispinosus, a species that require priority conservation in the Abrolhos Bank. Therefore, we recommend the creation of a new no-take marine protected area that encompasses this site. Our results also indicated that reef fish recruitment may be influenced by deterministic processes and do not vary only stochastically.

Made available in DSpace on 2014-12-17T14:54:48Z (GMT). No. of bitstreams: 1 AntonioPMH.pdf: 3481703 bytes, checksum: 60ec6cc8df48e68b6c13c12104d289d6 (MD5) Previous issue date: 2008-08-08 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The use of the maps obtained from remote sensing orbital images submitted to digital processing became fundamental to optimize conservation and monitoring actions of the coral reefs. However, the accuracy reached in the mapping of submerged areas is limited by variation of the water column that degrades the signal received by the orbital sensor and introduces errors in the final result of the classification. The limited capacity of the traditional methods based on conventional statistical techniques to solve the problems related to the inter-classes took the search of alternative strategies in the area of the Computational Intelligence. In this work an ensemble classifiers was built based on the combination of Support Vector Machines and Minimum Distance Classifier with the objective of classifying remotely sensed images of coral reefs ecosystem. The system is composed by three stages, through which the progressive refinement of the classification process happens. The patterns that received an ambiguous classification in a certain stage of the process were revalued in the subsequent stage. The prediction non ambiguous for all the data happened through the reduction or elimination of the false positive. The images were classified into five bottom-types: deep water; under-water corals; inter-tidal corals; algal and sandy bottom. The highest overall accuracy (89%) was obtained from SVM with polynomial kernel. The accuracy of the classified image was compared through the use of error matrix to the results obtained by the application of other classification methods based on a single classifier (neural network and the k-means algorithm). In the final, the comparison of results achieved demonstrated the potential of the ensemble classifiers as a tool of classification of images from submerged areas subject to the noise caused by atmospheric effects and the water column / A utiliza??o de mapas, derivados da classifica??o de imagens de sensores remotos orbitais, tornou-se de fundamental import?ncia para viabilizar a??es de conserva??o e monitoramento de recifes de corais. Entretanto, a acur?cia atingida no mapeamento dessas ?reas ? limitada pelo efeito da varia??o da coluna d ?gua, que degrada o sinal recebido pelo sensor orbital e introduz erros no resultado final do processo de classifica??o. A limitada capacidade dos m?todos tradicionais, baseados em t?cnicas estat?sticas convencionais, para resolver este tipo de problema determinou a investiga??o de uma estrat?gia ligada ? ?rea da Intelig?ncia Computacional. Neste trabalho foi constru?do um conjunto de classificadores baseados em M?quinas de Vetor de Suporte e classificador de Dist?ncia M?nima, com o objetivo de classificar imagens de sensoriamento remoto de ecossistema de recifes de corais. O sistema ? composto por tr?s est?gios, atrav?s dos quais acontece o refinamento progressivo do processo de classifica??o. Os padr?es que receberam uma classifica??o amb?gua em uma determinada etapa do processo s?o reavaliados na etapa posterior. A predi??o n?o amb?gua para todos os dados aconteceu atrav?s da redu??o ou elimina??o dos falsos positivos. As imagens foram classificadas em cinco tipos de fundos: ?guas profundas, corais submersos, corais intermar?s, algas e fundo arenoso. A melhor acur?cia geral (89%) foi obtida quando foram utilizadas M?quinas de Vetor de Suporte com kernel polinomial. A acur?cia das imagens classificadas foi comparada, atrav?s da utiliza??o de matriz de erro, aos resultados alcan?ados pela aplica??o de outros m?todos de classifica??o baseados em um ?nico classificador (redes neurais e o algoritmo k-means). Ao final, a compara??o dos resultados alcan?ados demonstrou o potencial do conjunto de classificadores como instrumento de classifica??o de imagens de ?reas submersas, sujeitas aos ru?dos provocados pelos efeitos atmosf?ricos e da coluna d ?gua

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Os fatores que explicam a distribuição observada em plantas e animais é uma pergunta que intriga naturalistas, biogeógrafos e ecólogos há mais de um século. Ainda nos primórdios da disciplina de ecologia, as tolerâncias ambientais já haviam sido apontadas como as grandes responsáveis pelo padrão observado da distribuição dos seres vivos, o que mais tarde levou à concepção de nicho ecológico das espécies. Nos últimos anos, o estudo das distribuições dos organismos ganhou grande impulso e destaque na literatura. O motivo foi a maior disponibilidade de catálogos de presença de espécies, o desenvolvimento de bancos de variáveis ambientais de todo o planeta e de ferramentas computacionais capazes de projetar mapas de distribuição potencial de um dado organismo. Estes instrumentos, coletivamente chamados de Modelos de Distribuição de Espécies (MDEs) têm sido desde então amplamente utilizados em estudos de diferentes escopos. Um deles é a avaliação de potenciais áreas suscetíveis à invasão de organismos exóticos. Este estudo tem, portanto, o objetivo de compreender, através de MDEs, os fatores subjacentes à distribuição de duas espécies de corais escleractíneos invasores nativos do Oceano Pacífico e ambas invasoras bem sucedidas de diversas partes do Oceano Atlântico, destacadamente o litoral fluminense. Os resultados mostraram que os modelos preditivos da espécie Tubastraea coccinea (LESSON, 1829), cosmopolita amplamente difundida na sua região nativa pelo Indo- Pacífico demonstraram de maneira satisfatória suas áreas de distribuição nas áreas invadidas do Atlântico. Sua distribuição está basicamente associada a regiões com alta disponibilidade de calcita e baixa produtividade fitoplanctônica. Por outro lado, a aplicação de MDEs foi incapaz de predizer a distribuição de T. tagusensis (WELLS,1982) no Atlântico. Essta espécie, ao contrário de sua congênere, tem distribuição bastante restrita em sua região nativa, o arquipélago de Galápagos. Através de análises posteriores foi possível constatar a mudança no nicho observado durante o processo de invasão. Finalmente, o sucesso preditivo para T. coccinea e o fracasso dos modelos para T. tagusensis levantam importantes questões sobre quais os aspectos ecológicos das espécies são mais favoráveis à aplicação de MDEs. Adicionalmente, lança importantes ressalvas na utilização recentemente tão difundida destas ferramentas como forma de previsão de invasões biológicas e em estudos de efeitos de alterações climáticas sobre a distribuição das espécies. / The factors underpinning the observed distribution of plants and animals across time and space are a central question in ecology and has intrigued scientists for over a century. But even back on those early times, the role of climatic tolerances of the species were recognized as one of the main explanations for such distributional patterns. Later, these assumptions gave rise to the concept of niche which triggered several advances in the study of natural history. Recently, these studies were addressed in the light of novel computational techniques capable of providing potential distributional maps for a given species, generically called Species Distribution Models (SDMs). This coupled with the broader availability of species occurrence records and of environmental data from international databases made studies with SDMs very popular and ubiquitous in the literature. One of the main uses of the SDMs approach is the assessment of potentially susceptible areas of invasion by non- indigenous species. Therefore, here we used SDMs to better understand the major factors related to the current distribution of two well established invasive scleractinian coral species in the Atlantic, both from the Pacific Ocean. The results showed that the models were successful in predicting the potentially invaded sites by the cosmopolitan Tubastraea coccinea (LESSON, 1829), broadly distributed throughout the Pacific. This species distribution was basically associated with increasing concentrations of calcite and lower levels of phytoplankton activity. However, the models were incapable of predicting the survival and establishment of T. tagusensis (WELLS, 1982) in the Atlantic. This species, unlike its congener, has a very restricted distribution in its native regions, the Galapagos Islands. A posterior analyzes indeed showed a niche shift during the invasion event of T. tagusensis in the Atlantic. Finally, the good modelling results for T. coccinea contrasted with the failure of modelling T. tagusensis invasion highlight important explanations on methodological procedures in SDMs. It also helps to better understand which ecological aspects of the species are favourable toward good modelling performance. In addition to that, these results calls for precaution when analyzing SDMs results, particularly in invasion and climate change scenarios studies.

Les poissons herbivores jouent un rôle écologique majeur face au phénomène de « coral-algal phase-shift », qui sévit depuis le début des années 80 dans les récifs coralliens de la Caraïbe. Dans cette étude, les habitudes alimentaires des principales espèces de poissons herbivores ont été étudiées afin de comprendre comment ces espèces utilisent et se partagent les ressources trophiques en milieu récifal et dans les herbiers. Les niches trophiques de ces espèces ont été décrites par deux méthodes complémentaires: les analyses des contenus des tractus digestifs et les analyses des isotopes stables du carbone C3C/ 12C) et de l'azoteCSN/ '4N). La qualité nutritionnelle des sources alimentaires a été évaluée par leurs concentrations de macronutriments (protéines, lipides, glucides solubles et insolubles) afin d'expliquer en partie le choix des ressources par les herbivores. Parmi les 14 espèces de poissons étudiées, appartenant aux familles des Pomacentridae, des Acanthuridae et des Scaridae, huit types de niches trophiques ont été décrits, indiquant une diversité fonctionnelle de ces espèces. Les niches trophiques décrites sont occupées par une ou plusieurs espèces, indépendamment de leur morphologie et de leurs affinités taxinomiques. Les résultats de cette étude suggèrent une complémentarité entre ces espèces, en terme d'utilisation des ressources, et soulèvent la question de leur conservation afin de préserver leur rôle écologique dans les écosystèmes côtiers de la Caraïbe. / Herbivorous fishes play a major ecological role against the « coral-algal phase-shift » phenomenon in the coral reefs of the Caribbean. In this study, the feeding patterns of the most important species of herbivorous fishes have been studied to understand how these species use and share the trophic resources on reefs and seagrass beds . Trophic niches of these species have been described by two complementary methods: the analyses oftheir digestive contents and the analyses of stable isotopes of carbon C3C/ J2C) and nitrogen (lsN/14N). The nutritional quality of the sources has been evaluated by their concentrations of macronutrients (proteins, lipids, soluble and insoluble carbohydrates) to explain partially the choice of resources by herbivorous fishes . Among the 14 studied species of herbivorous fishes (Pomacentridae, Acanthuridae and Scaridae), eight types of trophic niches have been described, indicating a functional diversity of these species . The trophic niches are occupied by one or several species, independently oftheir morphology or their taxonomie affinities. The results of this study suggest a complementarity among these species and raise the question of their conservation to preserve their ecological role on marine ecosystems of the Caribbean.

Les récifs coralliens de Nouvelle-Calédonie constituent un « hot-spot » de biodiversité marine et sont classés au patrimoine mondial de l’Unesco depuis 2008. Ces récifs sont dans un bon état général, mais ils sont soumis à des pressions anthropiques de plus en plus intenses, engendrées par un développement industriel (mines de nickel) et urbain croissant.Mieux comprendre le fonctionnement des écosystèmes lagonaires calédoniens est donc devenu un enjeu majeur. Ce travail s’inscrit dans cette démarche, avec pour objectifs principaux : (1) de reconstruire l’architecture des réseaux trophiques de ces écosystèmes (méthode des isotopes stables), (2) de déterminer leurs niveaux de contamination en éléments traces métalliques et en polluants organiques, et (3) de décrire l’intégration et le cheminement de certains de ces contaminants en leur sein. L’étude des écosystèmes récifo-lagonaires et de leurs réseaux trophiques a été réalisée au travers du prisme de prédateurs méconnus de hauts rangs trophiques : les poissons anguilliformes (murènes, congres et poissons-serpents). Pour ce faire, différentes sources de matière organique (MO) et divers consommateurs, parmi lesquels les poissons anguilliformes, ont été prélevés dans plusieurs sites répartis sur un gradient côte-large et provenant de deux zones du lagon sud.Quatre réseaux trophiques ont été identifiés au cours de ce travail. La voie benthique basée sur la MO du turf algal est la voie trophique majeure, commune à tous les poissons anguilliformes. L’utilisation complémentaire de la voie benthique sédimentaire et de la voie « pélagique lagonaire », est également mise en évidence avec une importance variable selon les espèces. En revanche, la MO provenant des phanérogames marines n’est intégrée qu’indirectement, par le biais de la voie détritique. Les différentes espèces d’anguilliformes appartiennent donc à des réseaux trophiques en partie divergents selon leur habitat (substrat dur ou meuble) et leur régime alimentaire (micro-, macrocarnivore ou piscivore). Ces prédateurs de hauts niveaux trophiques, consommant principalement des crustacés et des poissons mais également occasionnellement des annélides polychètes et des céphalopodes, se révèlent pour la plupart opportunistes. Une compétition entre certaines espèces est soulignée par le recouvrement de leurs niches trophiques. Les sources de MO et les consommateurs récifaux du lagon calédonien accumulent des concentrations modérées à fortes en éléments traces d’origine agricole, urbaine et minière. La bioaccumulation dépend des propriétés physico-chimiques du contaminant lui-même et des caractéristiques propres à l’organisme (taille, habitat, régime alimentaire, etc.). Ainsi, les contaminants sont répartis différemment entre les compartiments, et seuls Hg et As sont bioamplifiés le long des réseaux trophiques. Une contamination du lagon par les polluants organiques est également soulignée. Bien que les concentrations mesurées chez les poissons anguilliformes restent relativement faibles, l’étendue spatiale de cette contamination, ainsi que la détection de pesticides très toxiques dont l’utilisation est interdite (DDT), attestent de la nécessité à considérer cette pollution avec attention. Toutes ces considérations renforcent l’importance de mener un suivi à long terme des contaminations d’origines diverses en relation avec le fonctionnement trophique des systèmes récifo-lagonaires. / New Caledonian coral reefs constitute a « hot spot » of marine biodiversity and were registered World Heritage by UNESCO in 2008. These reefs are in good health, but they are subject to intense anthropic threats, induced by the increase of industrial (nickel mining) and urban development. A better understanding of the functioning of the Caledonian coral reefs has become a major issue. This work is part of this approach, with as main goals to: (1) reconstruct the architecture of food webs of these ecosystems (stable isotope method), (2) determine their contamination levels in metallic and organic contaminants and (3) describe integration and pathways of some of these contaminants through the food webs. The description of ecosystems and their food webs was carried out by the study of unknown predators: the anguilliform fish (moray, conger and snake eels). Different sources of organic matter (OM) and consumers, including anguilliform fish, were sampled in several sites distributed over a coast to barrier reef gradient within two areas of the south lagoon. Four food webs were identified. The benthic pathway based on the algal turf OM is the main food web, common to all anguilliform fish. The complementary use of benthic sedimentary (SOM) and “lagoon pelagic” (POM) food webs, is also highlighted with variable importance according to species. In addition, OM from seagrasses is included indirectly by the detrital pathway. The numerous anguilliform fish species belong to diverse food webs in part, depending on their habitat (hard and/or soft bottom) and their diet (micro/macro carnivores or piscivores). These predators of high trophic level, consuming mainly crustaceans and fish but also more occasionally annelids and cephalopods, are mostly opportunistic. A competition between some species is underlined by the overlap of their trophic niches. Sources of OM and consumers of the Caledonian coral reefs accumulate moderate to strong concentrations of trace elements issued from agricultural, urban and mining origins. Bioaccumulation depends on both physical and chemical properties of the contaminant and the organism’s own characteristics (size, habitat, diet, etc.). So, contaminants are distributed differently between compartments and only Hg and As are biomagnified along food webs. Contamination of the lagoon by organic pollutants is also pointed out. Even if concentrations measured in anguilliform fish are rather low, widespread contamination, plus the detection of toxic and forbidden pesticides (DDT), confirm the necessity to include this pollution in further studies. All these considerations reinforce the importance of setting up a long-term tracking system of contamination from diverse origins, linked with the trophic functioning of food webs.