Marine Fungi and Their Diversity in Coral Reefs

Reef-building corals support a wide range of species from microorganisms to reef sharks and manta rays. However, the impact of anthropogenic stress is beginning to show, with increases in the frequency of coral bleaching having knock-on effects for the wider reef community. In recent years, research has begun to show interest in the role microbes play within reefs. Some are suggesting they may hold the answer to the crisis that is unfolding (e.g. the use of microbes to mitigate heat stress or disease susceptibility in corals) (Peixoto et al., 2021). To date, most of this research has focused on prokaryotes and the coral algal symbionts, Symbiodiniaceae, while other microbial groups such as protists and fungi have received considerably less attention (Ainsworth et al., 2017; Bonacolta et al., 2023). The few studies that have explored the impacts of fungal communities on corals have tended to focused on the pathogenic nature (Le Campion-Alsumard et al., 1995), and only recently have people proposed they may be beneficial although a lot is still unknown (Roik et al., 2022). This thesis addresses several aims, including, aiming to further understanding of fungal diversity throughout the coral, as well as aiming to understand how fungal communities within the coral respond to external factors, all of which intend to increase our overall understanding of fungi in corals. Chapter 1 consists of an overview of our knowledge of fungi in the marine environment and fungi associated with corals. Chapter 2 explores how fungal diversity is distributed across coral compartments by separating different compartments (mucus, tissue and skeleton), and using molecular techniques to identify the fungal species found in each compartment. Here I found there were significant differences of the fungal diversity between the compartments (mucus and skeleton), but not between the mucus and tissue and the tissue and skeleton. There were also similarities between mucus and the surrounding environmental pools (sediment and water). In Chapter 3, the final chapter, spatial and temporal factors affecting coral fungal diversity were investigated, by collecting samples from multiple reefs, over multiple time points and across different depths, using molecular techniques to analyse the fungal communities. Surprisingly and in contrast to bacteria, the mycobiome was unchanged across space and time. However, similarities between the fungal diversity found in the coral mucus and the environmental pools of in situ corals were shown, supporting the findings of Chapter 2, which also saw similarities between the fungal communities in the mucus and environmental pools. Therefore, this thesis adds to our understanding of coral associated fungal species in terms of compartmentalisation and response to temporal and spatial factors.