Corals are habitat-forming species that support highly diverse benthic communities by providing shelter, breeding grounds and food sources for a wide range of marine species. They are key organisms to ecosystem structure and function but are currently severely threatened by several anthropogenic pressures linked to the climate crisis. Marine heat waves are becoming more intense and frequent in the Mediterranean and are causing mass mortality events in many marine communities, coral habitats among them. Degradation and loss of corals is causing a functional shift towards simplified habitats with significantly decreased biodiversity. Corals host a large, diverse, and abundant microbial community that has a strong influence on the evolution, physiology, and ecological functions of the coral host.

The study of the coral holobiont (the coral and its microbiome) has mainly focused on the bacterial community or the Symbiodiniaceae photosymbionts, leaving the vast majority of the protist community overlooked and creating an extensive gap in our understanding of the coral holobiont, and therefore coral habitats as a whole. We do not know much about the protistan symbionts' diversity, their location, and their morphological and genomic diversity. Past studies have shown that they play an important role in coral’s resistance to heat waves, suggesting that having information on them could provide insights to plan better conservation strategies of coral habitats. In this project, we aim to explore coral protists symbionts by doing a molecular characterization, a phylogenetic assignment and a community analysis of their diversity (Aim 1).

Furthermore, we also aim to understand how abundant these coral protists symbionts are and their location within the coral holobiont (Aim 2). Finally, our third goal is to do a morphological and transcriptomic characterization of coral protists symbionts to explore their morphological and functional diversity (Aim 3), since there is very limited genomic information on protistan symbionts. Throughout the project, we will develop and optimize several methodologies to reach these aims, which we expect will fill the enormous gap that represents the absence of protists in the current conceptual frameworks used to study corals and their resilience in front of the current climate crisis..