Coral tumors are atypical skeletal forms found on coral reefs worldwide. Here we present an analysis of the microbial communities associated with skeletal tumors on the coral Porites compressa. Microbial growth rates on both healthy and tumorous P. compressa were decoupled from the surrounding water column. Microbial communities associated with tumorous colonies had a significantly faster growth rate than those associated with healthy P. compressa. The microbial community associated with the tumors contained more culturable Vibrio spp. and could utilize more carbon sources than the microbes associated with healthy colonies. Presence of tumors affected the composition and dynamics of the microbial population associated with the entire colony.