Probiotics reshape the coral microbiome in situ without affecting the surrounding environment

The use of Beneficial Microorganisms for Corals (BMCs), or coral probiotics, has been validated in laboratory trials as a microbial therapy to enhance coral health and resilience to climate change and other impacts. Here, we present the first in situ application of a BMC consortium. Colonies of Pocillopora verrucosa from a central Red Sea reef were repeatedly inoculated over a period of three months and fragments were collected at four time points to assess bacterial community, algal photosynthetic capacity, and coral holobiont thermal thresholds. Microbiome analyses via 16S rRNA gene-based amplicon sequencing revealed a significant effect of the probiotic treatment on coral-associated bacteria, but not on the microbiomes of the surrounding seawater or sediments.