The present study carried out a detailed assessment of the metazoan parasite fauna in Boops boops (Sparidae) along the Spanish coasts off the Western Mediterranean and North-East Atlantic, which provided taxonomically consistent dataset comprising three levels of parasite community organisation that allowed questions regarding the structure of parasite communities to be addressed. The diversity of the parasite fauna of B. boops appeared to be higher than previously thought, as evidenced by the description of one new species, Wardula bartolii Pérez-del-Olmo et al., 2006 and the recovery of 53 parasite species (25 new host records). The complete checklist of parasites of this host throughout its distributional range comprises 78 species and 365 host-parasite-area records. A group of nine species with a wide geographical distribution was identified as the core of the parasite fauna of B. boops. The regional parasite fauna of B. boops was richest in the North-East Atlantic. There was a clear separation of the North-East Atlantic and Mediterranean local faunas, with a transition location occupying an intermediate position. Local parasite faunas were generally diverse. There was a high representation of parasites with complex life-cycles, transmitted via food ingestion, mostly trematodes. The phylogenetic influence on the parasite communities in B. boops is rather weak, since generalist parasites comprised a considerable part of communities. The species of the core parasite fauna of B. boops were already present in juvenile fish, whereas all species added to communities in larger fish were rare/accidental. The observed sequence of species appearance and persistence supported the hypothesis that species with wide geographical distributions appear in the fish population earlier than rare/stochastic species. Parasite communities were rich and abundant from an early age. Six species of the core parasite fauna of B. boops were identified as key parasites in developing communities since they persisted as common in all size cohorts and represented the majority of the individuals. A nested subset pattern was found which could not be completely attributed to either accumulation over time or segregation of the parasite species among different host cohorts. Nestedness was strongly related to the differential species abundance, suggesting that passive sampling could be the mechanism leading to this non-random structure. The data revealed that the geographical distance and the region affect the species composition and structure of parasite faunas and component communities in B. boops. The distance between localities/regions contributed significantly to the decay of the similarity estimated from parasite abundance at the infracommunity level. The structured spatial patterns were consistent in time but not across seasons. The spatial synchrony observed was solely due to the assemblage of the core species, supporting the hypothesis that widespread species would be strongly associated with patterns of variation in environmental conditions. The interspecific abundance-distribution patterns were recognized as the most important for the distance-decay relationship of similarity in this system due to the strong correlations observed at all scales of analysis. The comparative analyses revealed a notable alteration of parasite abundance patterns and dramatic changes in community richness, abundance and structure of parasite communities in B. boops studied after the Prestige oil-spill. A directional trend in parasite community succession was detected. However, the differences were still large indicating that shifting pollution baselines probably affect community recovery. The elevated levels of monoxenous infections could indicate that changes in immune parameters of fish. The increase of heteroxenous may have reflected an enhancement of the populations of the mollusc and copepod hosts due to organic enrichment following the oil-spill. Focusing on higher taxonomic/functional levels and the use of multivariate statistical approach have proved to be very useful in studying the response of parasite communities to pollution. __________________________________________________________________________________________________ RESUMEN En la presente tesis doctoral se realizó un estudio exhaustivo de los metazoos parásitos de la boga, Boops boops (Sparidae) en la costa Mediterránea y Atlántica española. La diversidad parásita fue mucho mayor de lo que previamente se pensaba, como se evidenció en la descripción de una nueva especie y la presencia de 53 especies (incluyendo 25 nuevos registros). Se encontró regularmente un grupo de nueve especies de amplia distribución, que fueron considerados el núcleo de la parasitofauna de B. boops. Las faunas parásitas locales resultaron ser diversas y caracterizadas por una gran representación de parásitos generalistas y con ciclos vitales complejos. La secuencia de aparición y persistencia observada en el desarrollo de las comunidades parásitas apoyó la hipótesis de que las especies con distribución geográfica amplia aparecen en las poblaciones de peces antes que las raras y estocásticas. Las comunidades parásitas de B. boops fueron ricas y abundantes desde una edad temprana. Se detectó una estructura anidada fuertemente relacionada con una abundancia diferencial de las especies, sugiriendo que el muestreo pasivo de parásitos del hospedador podría ser el mecanismo responsable de esta estructura no-aleatoria. Tanto la distancia geográfica como la región de origen afectaron la composición de especies y la estructura de las faunas parásitas y comunidades componentes. El patrón de estructura espacial fue consistente en el tiempo pero no entre estaciones. La relación abundancia-distribución interespecífica fue el aspecto más importante en el declive de la similitud con la distancia. El análisis comparativo de las muestras de localidades afectadas por el vertido del petrolero Prestige reveló un cambio drástico en la riqueza, abundancia y estructura de las comunidades parásitas, así como una notable alteración de los patrones de abundancia. Se detectó una tendencia direccional en la sucesión de las comunidades parásitas tras el vertido. Sin embargo, las diferencias siguen siendo acusadas, lo que podría indicar un desplazamiento de los niveles base que estaría afectando la recuperación de las comunidades bentónicas y parásitas tras el vertido. Tanto el enfoque basado en niveles taxonómicos y funcionales superiores como la aproximación mediante análisis estadísticos multivariantes, resultaron ser muy efectivos para este tipo de estudios.