Bulk isotope data from sponges collected in Summerland Key in Florida between July 27 - August 19, 2021

Sponges represent one of the oldest extant animal phyla, and their associations with microbial symbionts have likely played a critical role in their success on oligotrophic coral reefs. For example, variation in the abundance, diversity, and community composition of microbiomes across host species may drive niche partitioning due to differential assimilation and recycling of nutrients across sponge species. Stable isotope analysis of bulk sponge tissue allowed us to test for evidence of partitioning of three major resource pools (dissolved organic matter: DOM, particulate organic matter: POM, and inorganic nutrients: NaHCO3 and NaNO3) among four emergent Caribbean sponge species. Results from bulk (holobiont tissue including both sponge and microbial cells) stable isotope analysis show niche partitioning, with strong interspecific variation in the relative exploitation of each resource pool. These results demonstrate that associations with microbial symbionts have facilitated niche partitioning by allowing host sponges to acquire and recycle diverse nutrient pools via unique mechanisms.