Memoria de tesis doctoral presentada por Alan Denis Fernández Valero para obtener el título de Doctor en Ciéncies Marines por la Universitat de Barcelona (UB), realizada bajo la dirección de la Dra. Esther Garcés Pieres y del Dr. Albert Reñé Vicente del Institut de Ciències del Mar (ICM-CSIC).-- 165 pages, [EN] Current knowledge of marine fungi is limited, marked by gaps in the understanding of their diversity, spatio-temporal patterns, and ecological roles within marine ecosystems. The underexplored nature of specific fungal groups, like chytrids occurring during phytoplankton blooms, and the lack of research in most marine regions, such as the Mediterranean Sea, emphasise the need for this thesis.
Consequently, the main objective of this doctoral thesis is to investigate the composition of the fungal community in the Mediterranean coastal ecosystem, with a focus on the basal fungal group Chytridiomycota (chytrids). The study sets for specific objectives: i) to evaluate the spatial distribution of Chytridiomycota diversity in various coastal areas during dinoflagellate proliferations; ii) to evaluate the temporal dynamics of the fungal community in epiphytic communities during benthic dinoflagellate proliferations and to investigate their interaction with hosts; and iii) to identify and describe new parasitic Chytridiomycota species associated with
their host proliferations.
The chytrid community in coastal environments is particularly dynamic and diverse, with a marked specificity towards their preferred hosts. These communities are more diverse and abundant in sediments and on macroalgae surfaces than in the water column. The relative abundance of chytrids increases in the water column during dinoflagellate proliferations, suggesting their opportunistic parasitic behaviour. In the laboratory, strains of four chytrid species, including the most abundant species detected by metabarcoding sequencing, have been cultured and identified by co-culture techniques with dinoflagellates. Three strains correspond to as yet undescribed species and the cultures have allowed the morphological and molecular characterisation of two of them, Dinomyces gilberthii and Paradinomyces evelyniae, which have been newly described in this thesis. In terms of geographic distribution of species, Dinomyces gilberthii is widely distributed in coastal Mediterranean habitats particularly during summer dinoflagellate blooms. Conversely, species like Paradinomyces evelyniae
exhibit a more limited distribution in these habitats. Investigations into the temporal dynamics of the fungal community on poorly explored niches such as biofilms in macroalgae, revealed an alternation in the abundance of fungal groups, significantly in uenced by the epiphytic dinoflagellates dynamics. Dominant chytrid species in these communities, such as Dinomyces arenysensis, exhibit adaptability in their survival strategies, including trophic versatility.
The findings demonstrate that chytrids play a significant role in the structuring of planktonic and benthic microbial communities in the coastal ecosystems, [ES] El conocimiento actual sobre los hongos marinos es limitado, marcado por la falta de conocimiento de su diversidad, patrones espacio-temporales y funciones ecológicas en los ecosistemas marinos. El desconocimiento sobre algunos grupos fúngicos específicos, como los quítridos presentes en proliferaciones fitoplanctónicas, y la falta de investigación en algunas regiones marinas, como el Mar Mediterráneo, enfatizan la necesidad de esta tesis. [...], Alan Denis Fernández Valero was supported by a predoctoral fellowship from the Spanish government (PRE2018-084893). The research was funded by projects COPAS (CTM2017-86121-R) and SMART (PID2020-112978GB-I00) from the Spanish government. The Severo Ochoa Centre of Excellence accreditation (CEX2019-000928-S) from AEI 10.13039/501100011033 is acknowledged, Peer reviewed