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Quinlan ZA, Remple K, Fox MD, Silbiger NJ, Oliver TA, Putnam HM, Kelly LW, Carlson CA, Donahue MJ, Nelson CE.2017. Fluorescent organic exudates of corals and algae in tropical reefs are compositionally distinct and increase with nutrient enrichment. PeerJ Preprints5:e3372v1https://doi.org/10.7287/peerj.preprints.3372v1
Dissolved organic matter (DOM) composition is a key determinant of microbial community metabolism and trophic nutrient transfer. On coral reefs, four primary groups of benthic organisms dominate photosynthetic production: corals, macroalgae, microphytobenthos, and encrusting algae on rubble, all of which exude significant quantities of DOM. We conducted a mesocosm experiment to characterize and contrast DOM exudates from these four organismal groups under three levels of continuous inorganic nutrient enrichment. We measured bulk dissolved organic carbon and nitrogen and the multivariate spectral characteristics of fluorescent DOM (fDOM). Moderate nutrient enrichment enhanced DOM exudation by all producers. Corals exuded rapidly accumulating DOM with a markedly high concentration of aromatic amino acid-like fDOM components that clearly distinguishes them from algal exudates, which were dominated by humic-like fDOM components and did not accumulate significantly. Our results emphasize the differences between coral and algae in their potential to influence microbial communities and metabolism in reefs.
Corals and algae support reef food webs and release a significant proportion of their primary production as dissolved compounds metabolized by planktonic and benthic microbes. Little is known about the composition of these compounds, how they may differ among producers or how nutrient availability may alter their production. This experiment contrasted the composition of fluorescent organics exuded by four coral reef benthic constitutents and measured the effects of nutrient enrichment on exudate release. While all producers released significant amounts of bulk and fluorescent organics, and nutrients stimulated exudation, coral exudates were distinctly enriched in aromatic amino acid-like compounds and accumulated faster. These findings clarify a mechanism whereby anthropogenic activities that alter benthic cover and nutrient pollution on reefs will influence microbial organic matter processing.
Supplemental Figures S1-S4 and Supplemental Tables S1-S2