Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Estudos de comunidades de esponjas marinhas são escassos no Brasil, sendo este trabalho pioneiro nessa abordagem para a Ilha Grande - RJ, um local de alta diversidade biológica. A estrutura das assembleias de esponjas marinhas e da comunidade bentônica marinha séssil foi avaliada, a partir de índices descritores de diversidade, em seis pontos da Ilha Grande e ilhas próximas, sendo três do lado continental e três do lado oceânico. As assembleias foram comparadas entre os diferentes lado e profundidade, através da contagem do número de indivíduos e área de cobertura por foto-quadrados. Paralelamente, as esponjas foram coletadas, fixadas e posteriormente identificadas através de metodologia e literatura especializada. Foi encontrado um total de 5.457 indivíduos, representando as Classes Demospongiae e Calcarea, distribuídos em 41 espécies e nove morfotipos, indicando maior diversidade para Lagoa Azul e menor para Parnaióca, sendo o local com maior riqueza a Ilha do Abraão. Dentre as espécies identificadas, quatro dominaram mais de 50% do total e 26 não alcançaram nem 5% da abundância absoluta. Análises de variância por GLM só evidenciaram diferença significativa para profundidade com substratos diferentes (F= 2,79; p<0,04), enquanto o fator lado (F= 2,23; p>0,16) e a interação entre os fatores (F= 1,17; p>0,38) não tiveram diferença estatística. As análises multivariadas de ordenação Cluster e MDS indicaram a formação de quatro assembleias de esponjas: 1) quatro locais com substrato não consolidado; 2) Lagoa Azul com substrato não consolidado; 3) locais oceânicos de substrato rochoso; e 4) locais continentais de substrato consolidado. Já para a comunidade geral, 49 espécies foram encontradas, sendo o Filo Porifera o de maior representatividade específica, apesar das macroalgas terem formado o grupo mais abundante. A comunidade bentônica foi dominada por quatro espécies, que juntas alcançaram média de 50% da cobertura bentônica: alga calcária incrustante, algas formadoras de tapete de turf, a esponja Iotrochota arenosa e o zoantídeo Palythoacaribaeorum. Estatisticamente, o lado continental se mostrou diferente do oceânico, o qual possui maior riqueza, diversidade e uniformidade de espécies, muito provavelmente pelo menor número de espécies dominantes e aliado a isso maior heterogeneidade de habitats, o que promove o aumento da diversidade. Quinze novas espécies estão sendo registradas para a Baía da Ilha Grande, sendo três novas espécies, as quais estão sendo descritas por especialistas, e 12 são novos registros de espécies ou gêneros para a região, evidenciando que a diversidade de esponjas marinhas na BIG é alta e ainda pouco conhecida e que a formação de assembleias pode ser devida a singularidade de cada local, implicando na necessidade de conservação dos costões rochosos da Ilha Grande e cercanias, a qual pode ser manejada através da realização de rápidos levantamentos sobre a riqueza e o número de indivíduos da espécie na região / Marine sponge community studies are scarce in Brazil and this is a pioneering study in this approach on Ilha Grande RJ, a high diversity region. The structure of marine sponges assemblages and sessile marine benthic organisms was evaluated from diversity descriptors index in six sites of Ilha Grande and nearby islands, three in continental side and three on oceanic side. Assemblages were compared between sides and depths counting number of individuals and its coverage area by photo-quadrats method. At the same time, the sponges were collected, fixed and, in lab, identified through specialized methodology and literature. There was a total of 5.457, representing Class Demospongiae and Calcarea, distributed in 41 species and nine morphotypes (50 possible species) with greater diversity to Lagoa Azul on the inside and lower for Parnaióca, outside, while Ilha do Abraão had the greatest richness. Among the identified species, four dominated more than 50% of the total and 26 did not reach even 5% of total abundance. General linear model (GLM) on ANOVA highlighted significant difference only between depths with different substrates (F=2.79; p<0.04), while side (F=2.23; p>0.16) and the interaction between factors did not have differences (F=117; p>0.38). Ordination multivariate analyses, Cluster and MDS, distinguished four sponge assemblages: 1) four sites with unconsolidated substrate; 2) Lagoa Azul with unconsolidated substrate; 3) oceanic sites with hard substratum; 4) continental sites with hard substrate. For the community, 49 species were found and Phylum Porifera was the highest specific representation, despite macroalgae have formed the most abundant group. Encrusting calcareous algae, turf algae, sponge Iotrochotaarenosa, exclusive of the continental side and zoanthid Palythoacaribaeorum added approximately 50% of the benthic cover in all sites. The sides were significantly different with highest richness, diversity and evenness for oceanic side while continental had more abundance of species, most probably due to fewer dominant species. Moreover, greater heterogeneity of habitats may promote increased diversity. The 15 new species now recorded which three are new for science and 12 represent new species or genus records for Ilha Grande Bay revealing this area as one of the highest diverse area in marine sponges from Brazil, despite the low knowlegment. Furthermore, this result implies the need to increase the preservation of the rocky shores of the region and shows that a quick survey of the number of species and their abundance is sufficient to manage a conservation area

A diversidade bacteriana pode ser estudada, combinando técnicas convencionais e técnicas que empreguem tecnologias modernas para sua melhor compreensão. O objetivo do trabalho foi analisar a diversidade de bactérias cultiváveis e não cultiváveis em amostras de água do mar coletadas no Canal de São Sebastião no período de agosto/2005 a março/2007. As bactérias marinhas foram quantificadas em Agar marinho e identificadas por seqüenciamento do gene 16S rDNA. A concentração dos grupos a-, b-, g- e s-proteobacteria foi verificada através da técnica de FISH. A comunidade total foi analisada através da construção de três bibliotecas mensais (novembro/2006, fevereiro/2006, fevereiro/2007). O seqüenciamento identificou 87% das bactérias marinhas como Vibrio sp. A técnica de FISH detectou maior concentração de b-proteobacteria (10,2%), em relação ao número de células totais (DAPI) que variou de 7,0x106 a 2,3x107 céls/mL. As bibliotecas de clones foram compostas pelos filos Proteobacteria, Bacteroidetes, Cyanobacteria, Firmicutes, Fusobacteria, Verrucomicrobia e Chloroflexi. / Microbial diversity can be studied by a combination of techniques of both conventional and modern approaches for better understanding. The aim of this study was analyze marine bacteria culturable and nonculturable diversity from seawater samples collected at São Sebastião Channel during August 2005 to March 2007. Marine bacteria were quantified using Marine Agar and identified by 16S rRNA sequencing. Concentration of a-, b-, g- e s-proteobacteria group was verified through three clones library monthly (November 2006, February 2006, February 2007). The sequencing identified 87% of marine bacteria such as Vibrio sp. The FISH technique to detect higher concentration of b-proteobacteria (10.2%), compared to number total cells (DAPI) which range from 7.0 x 106 to 2.3 x 107 cells/mL. Clones library were composed of the phylum Proteobacteria, Bacteroidetes, Cyanobacteria, Firmicutes, Fusobacteria, Verrucomicrobia e Chloroflexi.

La falta de infraestructuras donde se promuevan iniciativas sobre la conservación de áreas protegidas: islas Palomino y Cavinzas, cuya fauna en estatus vulnerable es debido a la contaminación por plástico, da cuenta de la acción ausente del Estado sobre la Ordenanza Regional del Callao N° 003 por promover su conservación. Es así como la propuesta del Proyecto RE+ consiste en reinterpretar, revalorar y reintegrar la ciudad con el entorno natural marino y como resultado, ser un dispositivo integrador entre ambos escenarios, lo que atribuye incluso a una reflexión crítica del uso de suelo actual y relación espacial con los usuarios del distrito La Punta, remate de la Costa Verde con proyección de alcance metropolitano y denominada zona ecoturística; no siendo aprovechada en términos urbanos como fuente de activación del desarrollo económico y turístico. Este centro de interpretación propone una revaloración de la biodiversidad marina a través del desarrollo local como medio de conservación y el turismo como reactivador del Patrimonio; donde el diseño arquitectónico parte de una experiencia única de interpretación de ambos usuarios y la activación de espacios públicos que permitan dinamizar la contemplación, recreación y a su vez la revaloración por parte del usuario con su medio ambiente; que mitigue la degradación ambiental-cultural actual sobre nuestros océanos y vida marina. Siendo necesaria en esta investigación el ámbito sociocultural, económico y ambiental, en la búsqueda del uso de la arquitectura y espacio urbano con el fin de conservar la biodiversidad marina. / The lack of infrastructure to promote initiatives on the conservation of protected areas: Palomino and Cavinzas Islands, whose fauna in vulnerable status is due to plastic pollution, gives an account of the state's absent action on the Regional Callao Ordinance N° 003 to promote its conservation. This is how the RE+ Project's proposal consists in reinterpret, reassess and reintegrate the city with the marine natural environment and as a result, be an integrative device between the two scenarios, which attributes even to a critical reflection of current ground use and spatial relationship with users of the La Punta district, final top of the Costa Verde with projection of metropolitan scope and referred ecotourism zone; not being used in urban terms as a source of activation of economic and tourist development. This interpretation center proposes a reassessment of marine biodiversity through local development as a means of conservation and tourism as a reactivator of Heritage; where the architectural design starts from a unique experience of interpretation for both users and the activation of public spaces that make it possible to stimulate contemplation, recreation and, in turn, the reassessment by the user with their environment; that mitigates the current environmental-cultural degradation of our oceans and sea life. Being necessary in this research the sociocultural, economic and environmental field, in the search for the use of architecture and urban space in order to conserve marine biodiversity. / Tesis

Subsistence fishing is impacting on freshwater and marine biodiversity to the extent of extinction of some fish species. These illegal subsistence fishermen have created a huge impact on marine biodiversity, irrespective of marine and riverine laws that are put in place and practiced. There have been attempt to provide subsistence fishing extension officer services to facilitate in bringing subsistence fishermen fully into the management system, in an orderly and equitable manner, by facilitating the granting of formal subsistence fishing right, providing permits via policy management and effective rules via permit applications. However the follow up process as to whether these policies and rules administered is effective or not has not been measured. This investigation attempts to identify potential fishing that should be considered as suitable for subsistence fisheries in selected highly exploitable areas. Though it cannot be confirmed from previous studies that some relevant organizations are not fully taking their responsibilities, the study will further enable exploration of options and challenges associated with future management of subsistence fisheries and provide recommendations to enable proper implementation of the policies and legislations. / Environmental Sciences / M. Env. Sc. (Agriculture and Environmental Affairs)

Marine protected areas (MPAs) cannot be managed outside the context of human societies that are dependent on their associated ecosystems and resources. This means that local people’s perceptions need to be considered in the establishment of MPAs as well as their subsequent management, planning and decision making processes. Accordingly, this study investigated respondents’ perceptions of the Ponta do Ouro – Kosi Bay MPA. The MPA is part of the now proclaimed Lubombo Trans-frontier Conservation Area (TFCA). An interviewer - administered questionnaire was used to obtain primary data from 35 respondents, all resident in the study area and who are involved in various activities based on the coastal area and its marine resources. The focus of the study was on awareness regarding the establishment, impacts of the MPA, the setting of priorities for the MPA and lastly, respondents’ roles and responsibilities The findings from the study reveal low levels of awareness of the establishment of the MPA among respondents, although there was acknowledgement of its potential contribution to biodiversity conservation. Various types of impacts of the establishment of the MPA were noted. The establishment of the MPA was perceived to negatively impact on the access to, and use of, marine resources. It was also felt that the MPA would impact on the exercise of traditional authority. Concerning the setting of future priorities for the MPA, socio-economic considerations, particularly job creation rated highest. Biodiversity conservation ranked highest in terms of factors that should shape the current priorities of the MPA. Overall, tourism and related job creation and biodiversity conservation were identified as the main opportunities associated with the establishment of the MPA. Controlling access to the area, curbing inappropriate resource use, controlling development and ensuring that local people benefit were highlighted as major opportunity benefits. Constraints were mainly considered in relation to the exercise of traditional leadership, access to the area and restrictions in selling of harvested marine resources. Regarding how to collaborate in the MPA, various skills among the respondents were mentioned, with respect to the following areas: enforcement (control, patrols and security) and community relations and awareness (including communication and the translation of documents). Lastly, while the respondents displayed both supportive and unsupportive attitudes as results of perceptions of the intended MPA, in an overall sense, the MPA was considered as a positive development. This was in spite of the perceived weak communications that exist at present between the authorities and local people. Enhanced, communication between authorities in charge of the MPA and local people could help to provide a more positive sentiment towards the MPA. This is particularly true of the local people who, if they understood the rationale for the MPA more fully and how it would impact on their use of the resources of the MPA, would be more likely to support its establishment and existence. / Thesis (M.Env.Dev.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.

Subsistence fishing is impacting on freshwater and marine biodiversity to the extent of extinction of some fish species. These illegal subsistence fishermen have created a huge impact on marine biodiversity, irrespective of marine and riverine laws that are put in place and practiced. There have been attempt to provide subsistence fishing extension officer services to facilitate in bringing subsistence fishermen fully into the management system, in an orderly and equitable manner, by facilitating the granting of formal subsistence fishing right, providing permits via policy management and effective rules via permit applications. However the follow up process as to whether these policies and rules administered is effective or not has not been measured. This investigation attempts to identify potential fishing that should be considered as suitable for subsistence fisheries in selected highly exploitable areas. Though it cannot be confirmed from previous studies that some relevant organizations are not fully taking their responsibilities, the study will further enable exploration of options and challenges associated with future management of subsistence fisheries and provide recommendations to enable proper implementation of the policies and legislations. / Environmental Sciences / M. Env. Sc. (Agriculture and Environmental Affairs)

Epibiosis is an ecological relationship that has been described as one of the closest possible associations in marine ecosystems. In the space limited rocky intertidal, mussel beds provide important secondary space for barnacles. The epibiotic relationship between mussels and barnacles on the south-east coast of South Africa was considered at different scales, from large-scale, natural patterns of epibiosis on the rocky shore, to fine-scale settlement choices of barnacles and the effects on the condition and growth rates of individual mussels. Mussel and barnacle assemblages were generally stable over a 12-month period. The tracking of individual mussels with and without barnacle epibionts resulted in a significant increase in mortality rate of mussels with epibionts over 12 months (two-way ANOVA, p = 0.028). Barnacles on rocks, as well as on mussels, were also tracked with no significant effect of substratum on mortality of barnacles (two-way ANOVA, p = 0.119). Prevalence and intensity of barnacle infestations was also examined in relation to coastline topography on two co-occurring mussel species, the indigenous Perna perna and invasive Mytilus galloprovincialis. The results were complex, but bay status had significant effects on prevalence and intensity for both mussel species, depending on the time and zone. The effect of bay in relation to time was particularly relevant for M. galloprovincialis (four-way nested ANOVA, Season X Site(Bay): p = 0.0002), where summer prevalence was higher than that of winter in bays, regardless of zone, while in open coast sites, the effect of season was only significant in the mid zone. Patterns of intensity generally showed higher values in summer. Substratum preference by barnacles was investigated by recording settlement, survival and mortality of Chthamalus dentatus barnacles on various treatments. There was a strong preference for the rock-like plastic substratum by primary settlers (pair-wise tests of PERMANOVA: Dead < Rock mimic (p = 0.0001); Replica < Rock mimic (p = 0.019) and Live < Rock mimic (p = 0.0001)). This indicates that barnacles settle on mussel shells only as a secondary choice and that micro-topography is an important variable in barnacle settlement. The effect of barnacle epibiosis on condition index and growth of P. perna and M. galloprovincialis was also examined as a direct indication of the health of mussels subjected to the biological stress of epibiosis. Although not significant (PERMANOVA: P. perna: p(perm) = 0.890; M. galloprovincialis: p(perm) = 0.395), growth for both mussel species was slower for barnacle-infested individuals in summer, which is the main growing season for mussels in the region. Results from condition index calculations, however, showed no negative impacts of epibiotic barnacles (three-way ANCOVA: P. perna: p = 0.372; M. galloprovincialis: p = 0.762). Barnacle epibionts create a new interface between the mussel and its environment and this interaction can affect other members of the community. The possibility of the barnacle epibiont causing increased drag also needs further investigation. Biological processes operating within a wide range of physical stressors drive the interactions on the rocky shore, such as epibiosis. Overall, the results of this study suggest that the epibiotic relationship between mussels and barnacles on the south-east coast of South Africa does not significantly affect the mussel species present and that barnacles only use mussel shells as a secondary choice of substratum.

Orientadores: Lúcia da Costa Ferreira, Cristiana Simão Seixas / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Filosofia e Ciências Humanas / Made available in DSpace on 2018-08-25T21:03:31Z (GMT). No. of bitstreams: 1 Araos_Francisco_D.pdf: 8695110 bytes, checksum: ba48abe9f0ebe07a654ee792894af637 (MD5) Previous issue date: 2014 / Resumo: Nas últimas décadas, a criação e implementação de Áreas Marinhas Protegidas têm-se intensificado nos diferentes oceanos do mundo. Como resposta à crise ambiental produzida pela sobre-exploração dos recursos pesqueiros, a poluição das zonas costeiras, a expansão das aglomerações urbanas nas áreas litorais e os impactos do aquecimento global, as Áreas Marinhas Protegidas aparacem como o instrumento chave para mitigar os impactos antropogênicos e promover a sustentabilidade marinha e costeira. No entanto, os conflitos causados pela imposição de áreas de proteção em zonas utilizadas por múltiplos usuários e a constatação do fracasso de muitas Áreas Marinhas Protegidas na conservação efetiva da biodiversidade, revelam a importância das dimensões humanas da conservação marinha. À luz deste problema de pesquisa, a presente tese de doutorado tem por objetivo analisar o processo decisório que define criação e implentação de duas Áreas Marinhas Protegidas na América do Sul: no Município de Navidad no Litoral Central do Chile e no Litoral Norte do Estado de São Paulo no Brasil. Os resultados da pesquisa demonstram a emergência de arenas ambientais para a conservação marinha com a finalidade de construir regras para regular os múltiplos usos dos recursos naturais e promover a sustentabilidade das zonas costeiras. Estas arenas cumprem um papel fundamental na explicitação dos conflitos e na promoção de pactos sociais, evidenciado os alcances e limites do processo democrático vivenciado nos dois países. Para além da biodiversidade, comprova-se que a conservação marinha representa uma oportunidade única para reorientar a trajetória de insustentabilidade até agora percorrida, assim como para experimentar novas formas de fazer democracia / Abstract: Over the last years the establishment of Marine Protected Areas has intensified worldwide. In response to the environmental crisis of the oceans produced by overexploitation of fishery resources, pollution of coastal areas, the expansion of urban agglomerations in coastal zone and the impacts of global warming, Marine Protected Areas are recognized as the key tool for mitigate anthropogenic impacts and promote the marine sustainability. Nevertheless, the conflicts triggered by the imposition of protected areas in zones used by multiple users and the failure of Marine Protected Areas improving effective biodiversity conservation, highlight the relevance of the human dimensions of marine conservation. Considering this problem the thesis aims to analyze the environmental decision-making process that defines the establishment and management of two Marine Protected Areas in South America: Municipalty of Navidad at the Central Coast of Chile and North Coast of the São Paulo State in Brazil. The study demonstrates the emergence of environmental arenas for marine conservation in order to regulate the multiples uses of marine resources and support the sustainability of the coastal zones. These arenas play a key role for the recognition of conflicts and the promotion of environmental social contracts, showing the advances and constrains of the democratic process in both countries. Beyond biodiversity, marine conservation represents an exceptional opportunity to redirect the paths of unsustainability, as well to experiment new democratic practices / Doutorado / Aspectos Sociais de Sustentabilidade e Conservação / Doutor em Ambiente e Sociedade

Under the growing demand for marine fish resources, and the apparent and expected impacts of global climate change, there is a need to conduct long-term monitoring (LTM) to ensure effective management of resources and conservation of biodiversity. However LTM programmes often suffer from design deficiencies and fail to achieve their objectives. These deficiencies stem from the fact that insufficient consideration is afforded to the design phase, with programmes selecting methods that are not suitable to address the objectives, or are not cost-efficient, compromising the sustainability of the LTM. To facilitate the establishment of LTM programmes along the southern coast of South Africa, background research needed to be conducted to identify which methods were most appropriate for LTM of reef fish. This study presents a detailed field-based assessment of the suitability and cost-efficiency of monitoring methods for long-term monitoring of reef fish in the Agulhas Ecoregion of South Africa. The approach adopted to identify the method, or suite of methods most suited for LTM, involved (i) the selection of methods considered suitable for LTM, (ii) the individual assessment and optimisation of method performance, and (iii) the comparative assessment of the fish community sampled by the different methods. The most suited method(s) were then identified as those that provide the most comprehensive assessment of the fish community and had the highest cost-efficiency. The research was conducted between January 2008 and 2011 in the Tsitsikamma and Table Mountain National Park (TNP and TMNP, respectively) marine protected areas (MPAs) within the Agulhas Ecoregion. The methods selected included fish traps (FT), controlled angling (CA), underwater visual census (UVC), remote underwater video (RUV), baited RUV (BRUV) and remotely operated vehicles (ROV). The individual assessment and optimisation was conducted with the FT, UVC, RUV and BRUV methods. The assessment of the FT method aimed to identify the optimal soak time, and whether or not the size of the funnel entrance to the trap affected the catch. The results identified that larger funnel entrances caught more fish and soak times of 80 minutes produced the highest catches per unit effort. However the data were highly variable and the method detected few of the species typical of the region. Fish traps were also associated with high levels of mortality of fish post-release. The assessment of UVC strip transect method involved directly comparing the precision of data collected by researchers and volunteers using a novel double-observer technique (paired-transects). The results showed considerable error in both the volunteers and researchers data, however the researchers produced significantly higher precision data, compared to the volunteers. The distinction between researchers and volunteers was not evident in the data for the dominant species of fish. For all observers, the abundance of a species in the sample had a significant influence on its detectability, with locally scarce or rare species poorly detected. UVC was able to sample the majority of species typical of reefs in the region, however it appeared plagued by observer and detectability biases. The assessments of RUV and BRUV were conducted simultaneously which enabled the assessment of the effect of bait on the observed fish community. In addition the optimal deployment time for both methods to maximise species richness and abundance was determined. The results showed that BRUV, and to a lesser degree RUV, were able to effectively survey the reef fish community for the region with a 50 minute and 35 minute deployment time, respectively. Baited remote underwater video was especially good at detecting the invertebrate and generalist carnivores, and cartilaginous species. On the other hand, RUV was more effective at surveying the microinvertebrate carnivores. Remote underwater video was characterised by higher data variability, compared to BRUV, and was ultimately considered a less cost-efficient monitoring method. Comparative methods assessments were conducted during two field experiments with the FT, UVC and BRUV methods in the TMNP MPA, and the FT, CA, UVC, RUV, BRUV and ROV methods compared in the TNP MPA. The objectives of the comparison were to investigate differences in the fish communities observed with the different methods, and to determine the power of the data to detect an annual 10% growth in the fish populations over a period of five years. The results from the method comparison were in turn used to conduct the cost-benefit analysis to determine the efficiency of the different methods at achieving monitoring objectives requiring population data from multiple trophic and functional groups with the community, and from species of fisheries importance. The results indicated that FT, CA and ROV were ineffective at monitoring the reef fish community, although CA appeared to provide valuable data for the dominant fisheries species. Both CA and FT required minimal initial investment however, the variability in the data translated into high annual monitoring costs, as the required sampling effort was great. The ROV required the highest initial investment and was identified as the least cost-efficient method. Underwater visual census was able to adequately survey the bony fish within the community, however it did not detect the cartilaginous species. Underwater visual census required a large initial investment and was not cost-efficient, as a many samples were required to account for the variability in the data. Remote underwater video provided a comprehensive assessment of the reef fish community, however it too was associated with high levels of variability in the data, compared to BRUV, reducing its cost-efficiency. BRUV provided the most comprehensive assessment of the reef fish community and was associated with the highest cost-efficiency to address the community and fisheries species monitoring objectives. During the course of this research stereo-BRUV has gained considerable support as an effective reef fish monitoring method. Although not tested during this research, stereo-BRUV is preferred to BRUV as it provides accurate data on the size of fish. However, the initial investment of stereo-BRUV is over three times that required for the BRUV. Although it is recommended that a baited video technique be used for LTM in the Agulhas Ecoregion, the choice between BRUV and stereo-BRUV will depend on the specific objectives of the programme and the available budget at the implementing agency.

Les diatomées sont des micro-algues unicellulaires, qui jouent un rôle primordial dans l’eco-système marin. En effet, elles sont responsables de 20% de l’activité photosynthétique sur Terre, et sont à la base de la chaîne alimentaire marine, toujours plus menacée par le changement climatique. Les diatomées établissent diverses interactions microbiennes avec des organismes issus de l’ensemble de l’arbre du vivant, à travers des méchanismes complexes tels que la symbiose, le parasitisme ou la compétition. L’objectif de ma thèse a été de comprendre comment ces interactions structurent la communauté du plancton, à grande échelle spatiale. Pour ce faire, j’ai développé de nouvelles approches basées sur le jeu de données inédit de Tara Océans, une expédition mondiale qui a exploré la diversité et les fonctions des microbes marins, en récoltant plus de 40.000 échantillons à travers 210 sites autour du monde. Grâce à l’analyse de réseaux de co-occurrence microbiens, je montre d’une part que les diatomées agissent comme des « ségrégateurs répulsifs » à l’échelle globale, en particulier envers les organismes potentiellement dangeureux tels que les prédateurs et les parasites, et d’autre part que la co-occurrence des espèces ne s’explique qu’en minorité par les facteurs environnementaux. Grâce à la richesse des données Tara Océans, j’ai par ailleurs permis la charactérisation d’une interaction biotique impliquant une diatomée et un cilié hétérotrophe à l’échelle de l’eco-système, illustrant de surcroît le succès des approches dirigées par les données. Dans l’ensemble, ma thèse contribue à notre compréhension des interactions biotiques impliquant les diatomées, de l’échelle globale à la cellule unique. / Diatoms are unicellular photosynthetic microeukaryotes that play a critical role in the functioning of marine ecosystems. They are responsible for 20% of global photosynthesis on Earth and lie at the base of marine food webs, ever more threatened by climate change.Diatoms establish microbial interactions with numerous organisms across the whole tree of life, through complex mechanisms including symbiosis, parasitism and competition. The goal of my thesis was to understand how those biotic interactions structure the planktonic community at large spatial scales, by using new approaches based on the unprecedented Tara Oceans dataset, a unique and worldwide circumnavigation that collected over 40.000 samples across 210 sites to explore the diversity and functions of marine microbes. Through the analysis of microbial association networks, I show that diatoms act as repulsive segregators in the ocean, in particular towards potentially harmful organisms such as predators as well as parasites, and that species co-occurrence is driven by environmental factors in a minority of cases. By leveraging the singularity of the Tara Oceans data, I provide a comprehensive characterization of a prevalent biotic interaction between a diatom and heterotrophic ciliates at large spatial scale, illustrating the success of data-driven research. Overall, my thesis contributes to our understanding of diatom biotic interactions, from the global patterns to the single cell.