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Ocean acidification is increasing and affects many marine organisms. However, certain sponge species can withstand low-pH conditions. This may be related to their complex association with microbes. We hypothesized that species with greater microbial diversity may develop functional redundancy that could enable the holobiont to survive even if particu- lar microbes are lost at low-pH conditions. We eval- uated the effects of acidification on the growth and associated microbes of three ubiquitous Mediterra- nean sponges by exposing them to the present pH level and that predicted for the year 2100. We found marked differences among the species in the acquisi- tion of new microbes, being high in Dysidea avara , moderate in Agelas oroides and null in Chondrosia reniformis ; however, we did not observe variation in the overall microbiome abundance, richness or diver- sity. The relative abilities to alter the microbiomes contributes to survivorship in an OA scenario as demonstrated by lowered pH severely affecting the growth of C. reniformis , halving that of A. oroides , and unaffecting D. avara . Our results indicate that functional stability of the sponge holobiont to with- stand future OA is species-specific and is linked to the species’ ability to use horizontal transmission to modify the associated microbiome to adapt to envi- ronmental change