CELLULAR RESOLUTION OF NUTRIENT UPTAKE AND RECYCLING INDICATES MICROBIOME COMPOSITION AFFECTS RESOURCE PARTITIONING AMONG CARIBBEAN SPONGES
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Jones II, Hal Hunt
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Marine sponges are dominant benthic organisms that range from the tropics to the poles, and from shallow waters to the deep sea. They are especially dominant on Caribbean coral reefs, where they often occupy greater percent cover than soft corals. However, the diversity and abundance of sponges in the Caribbean represent a paradox, as resources, especially nitrogen, are limiting. The ecological success of sponges on Caribbean coral reefs may thus be linked to the exploitation of novel and unique resources facilitated by microbial symbionts, but no study to date has tested whether microbiome composition contributes to the partitioning and recycling of both heterotrophic and autotrophic resources. To address this, we conducted three 75-hour pulse-chase experiments with four dominant Caribbean sponge species that targeted resource pools including both organic (dissolved and particulate) and inorganic matter enriched with 13C and 15N. Isotopic enrichment was measured in bulk sponge tissue to demonstrate differential uptake and retention of diverse sources of carbon and nitrogen through time. We also analyzed enrichment at the cellular level using nanoscale secondary ion mass spectrometry (nanoSIMS) to evaluate the role of the host and its symbionts in the processing of these resources. Enrichment in bulk tissue varied significantly among hosts across experiments and through time, as did enrichment within both sponge and microbial cells. Our results suggest links between divergence in sponge microbiomes and the ability to assimilate and recycle nutrients from diverse resources. This work supports the hypothesis that microbiome composition facilitates resource partitioning in Caribbean sponges, and thus contributes to the maintenance of sponge biodiversity in this ocean basin.