The giant barrel sponge, Xestospongia muta, is a high microbial abundance sponge on Caribbean coral reefs, living along shallow to mesophotic depth gradients where multiple abiotic factors (e.g., irradiance) change with depth. Samples of X. muta were collected along a depth gradient at Little Cayman (LC) and Lee Stocking Island (LSI) and the microbiome of these samples was analyzed using 16S rRNA (454) amplicon sequencing. The results show a significant shift in community structure from 10 to 91 m in LC sponges, but a similar shift was not detected in sponges from 10-60 m at LSI