Meeting Abstract
By hosting symbionts, many eukaryotes gain access to the products of microbial metabolism that are crucial for host performance. Within oligotrophic coral reefs, some (High Microbial Abundance [HMA]), but not all (Low Microbial Abundance [LMA]) sponges host such communities. Recent research has revealed substantial disparity in these sponge-microbe associations (termed holobionts), with substantial host specificity for particular symbiont taxa and functional differences in the C and N metabolism of microbial consortia within distinct hosts. To assess how metabolically diverse holobionts are distributed in isotopic niche space, we investigated the niche size (as standard ellipse area [SEAc]) and relative placement of 14 common sponge species in bivariate (δ13C and δ15N) plots. Sponges were collected at multiple sites within the recently explored reefs of the Miskito Cays of Honduras. These reefs support diverse communities of HMA and LMA species spanning a gradient of photosymbiont abundance, as revealed by chlorophyll a analysis. Although the SEAc of HMA sponges was larger than that of LMA, photosymbiont abundance was a better predictor of holobiont function than overall symbiont abundance, suggesting that autotrophic metabolism is an important process in the placement of species in isotopic space. We also observed substantial variation in the placement of individual species within isotopic niche space. We posit that hosting specific, functionally diverse symbiont communities may impact niche utilization across diverse holobionts, potentially contributing to the diversification of sponge communities within tropical reefs.
