Hidden Fungal Diversity of the Precious Mediterranean Red Coral Corallium rubrum

Corals maintain complex symbiotic relationships with diverse microorganisms, including fungi, which are often overlooked but represent a critical component of the coral holobiont. This study explores the fungal diversity associated with the tissue and skeleton of the red coral Corallium rubrum, a key species in Mediterranean Marine Animal Forests (MAFs). Using a culture-based approach, we recovered a broad spectrum of fungal diversity, dominated by Ascomycota such as Penicillium, Cladosporium and Aspergillus. The discovery of numerous taxa with known bioactive properties underscores the potential ecological and biotechnological relevance of coral-associated fungi. At the same time, the presence of species such as Aspergillus sydowii, which is considered pathogenic under elevated temperatures, raises concerns about coral vulnerability during increasingly frequent Mediterranean marine heatwaves. These taxa should be further investigated to evaluate their pathogenic potential. Overall, our results expand current knowledge of coral-fungal associations, providing a foundation for future work on their ecological significance, role in coral resilience and potential applications in biotechnology.