Characterizing the bacterial associates of three Caribbean sponges along a gradient from shallow to mesophotic depths.

Bacteriosponges have been shown to support relatively stable microbial communities across both distance and time, but little is known about the effect of depth on the composition of the associated community. To address this question, we examined the bacterial communities associated with three common Caribbean bacteriosponges collected at the same location over a depth gradient from approximately 10-100 m. The 16S rRNA genes of the associated communities were assessed using terminal restriction fragment length polymorphism and clone library analyses. Our results indicated that the stability and specificity of the associated bacterial communities varied with the host sponge but that each sponge supported a distinct community. Analyses of similarity suggested differences in community composition with depth, but examination of in silico predicted terminal restriction fragments failed to identify bacteria that occurred specifically at particular depths. Plakortis angulospiculatus, Agelas conifera, and Xestospongia muta supported diverse Chloroflexi species, while X. muta appeared to be the only sponge that hosted a cyanobacterial community. Regardless of host sponge, each species maintained a 'core' group of bacterial associates across a depth range with the composition of the remaining community presumably influenced by both biotic and abiotic factors.