What does microbiology tell us?
Each coral species is essentially a separate microbial universe, so studying just one type of coral (like Lophelia pertusa) doesn’t tell us everything we need to know. There are more species of corals in the deep-sea than there are in shallow tropical systems, and so far the bacterial associates of only a handful (less than 15) of deep-sea species have even begun to be characterised. What’s more, bacteria aren’t the only microbes associated with corals; there are also archaea, fungi, and protists. We know essentially nothing about those groups in deep-sea corals.
Why do we need to know about the coral-associated microbes? Coral diseases are caused by microbes; either invading pathogens or when some stressor destabilises the balance between the coral and it communal microbes. In order to know what has gone wrong when disease occurs, it helps a lot to know how the system functions when it is working properly.
Another reason is that the coral’s associated microbes are its first line of adaptation to change. The microbiome (all the genetic capabilities of all the coral associated microorganisms) can be altered in response to environmental stresses on the order of hours to days, compared to decades or centuries for genetic adaptations to manifest in the coral animal. Understanding coral microbiology, in terms of microbial-species diversity as well as metabolic capabilities, is critical to determining the resiliency of deep-sea corals to climate changes such as increasing water temperatures and ocean acidification.