Abstract Dynamic symbioses between the host, photosynthetic eukaryotes, and diverse prokaryotes are the foundation of corals’ ecological successes across highly diverse ocean habitats. This may be especially so in mesophotic corals which face unique environmental challenges when compared to shallow-water corals, for example, light levels that drive photosynthesis are significantly reduced. The success of reef-building corals in the mesophotic zone provides insights not only into the capacity of these populations to act as refugia but importantly the biological mechanisms that underpin coral success across divergent environmental regimes. The necessity in answering the fundamental questions—How do corals succeed in diverse habitats, and what is the contribution of all members of the metaorganism to coral function?—is underscored by uncertainty regarding the ability of reef corals to acclimate to rapid environmental changes. “Whole-system” or “whole-organism” studies provide a new direction for biological research in understanding the complexity of coral reef ecosystems and provide the capacity with which to unravel the biological basis of coral reef health and reef sustainability into the future. In this context, the mesophotic zone is of particular importance. Here, we review advances in understanding of the coral holobiont in the mesophotic zone, focusing on both eukaryotic and prokaryotic symbionts, and compare and contrast this to our understanding of shallow-water corals. In addition, we outline the challenges that remain in applying new technologies to advancing our understanding of these highly complex and valuable marine ecosystems.

Depth range
30- 150 m

Mesophotic “mentions”
51 x (total of 5220 words)

Classification
* Focused on 'mesophotic coral ecosystem'

Fields
Ecology
Evolution
Long-term monitoring
Management and Conservation

Focusgroups
Symbiodinium (zooxanthellae)
Viruses
Bacteria and Archaea