Beneficial properties of mucus in coral adaptations and ecological interactions

Abstract

Coral mucus secreted by mucocytes provides a protective physicochemical and physiological barrier between coral tissue and external environmental threats. The biomolecules and nutrients of the secreted mucus are derived from endosymbionts, coral polyps and support coral functions, such as feeding, sediment clearing and protection, against numerous biotic and abiotic stressors. The surface mucus layer also houses a diverse community of beneficial microorganisms that defend against pathogens. Enzymes including peptidases, esterases, and glycosidases were observed and described in mucus. Most importantly, the presence of phenoloxidase, an intracellular enzyme in secretory mucus, generally triggers melanin synthesis, providing fast-acting components of invertebrate immunity in disease resistance. However, the purpose and the mechanism of mucus release, effects of mucus components on defense properties, and functional roles in intra- and interspecific interactions are not well described. Thus, the present review aims to understand the mucus components and the complex roles played by mucus in microbial associations, feeding, and resilience that influence coral health.