Corals are animals that form close

Corals are animals that form close mutualistic associations
with endosymbiotic photosynthetic algae of the
genus Symbiodinium. Together they provide the calcium
carbonate framework of coral reef ecosystems. The
importance of the microbiome (i.e., bacteria, archaea,
fungi, and viruses) to holobiont functioning has only
recently been recognized. Given that growth and density
of Symbiodinium within the coral host is highly dependent
on nitrogen availability, nitrogen-cycling microbes
may be of fundamental importance to the stability of
the coral–algae symbiosis and holobiont functioning, in
particular under nutrient-enriched and -depleted scenarios.
We summarize what is known about nitrogen
cycling in corals and conclude that disturbance of microbial
nitrogen cycling may be tightly linked to coral
bleaching and disease.