INCREASING CORAL RESILIENCE TO BLEACHING THROUGH MICROBIOME MANIPULATION

Although the early coral reef-bleaching warning system (NOAA/USA) is
established, there is no feasible treatment that can minimize temperature
bleaching and/or disease impacts on corals in the field. Here, we present
the first attempts to extrapolate the widespread and well-established use
of bacterial consortia to protect or improve health in other organisms
(e.g., humans and plants) to corals. Manipulation of the coral-associated
microbiome was facilitated through addition of a consortium of native
(isolated from Pocillopora damicornis and surrounding seawater) putatively
beneficial microorganisms for corals (pBMCs), including five
Pseudoalteromonas sp., a Halomonas taeanensis and a Cobetia marina-related
species strains. The results from a controlled aquarium experiment in two
temperature regimes (26 °C and 30 °C) and four treatments (pBMC; pBMC with
pathogen challenge – Vibrio coralliilyticus, VC; pathogen challenge, VC;
and control) revealed the ability of the pBMC consortium to partially
mitigate coral bleaching. Significantly reduced coral-bleaching metrics
were observed in pBMC-inoculated corals, in contrast to controls without
pBMC addition, which displayed strong bleaching signs as indicated by
significantly lower photopigment contents
and Fv/Fm ratios. The structure of the coral microbiome
community also differed between treatments and specific bioindicators were
correlated with corals inoculated with pBMC (e.g., Cobetia sp.) or VC
(e.g., Ruegeria sp.). Our results indicate that the microbiome in corals
can be manipulated to lessen the effect of bleaching, thus helping to
alleviate pathogen and temperature stresses, with the addition of BMCs
representing a promising novel approach for minimizing coral mortality in
the face of increasing environmental impacts.