Introduction Caribbean mangrove-associated sponge communities are very distinct from sponge communities living on nearby reefs, but the mechanisms that underlie this distinction remain uncertain. It has been hypothesized that dissolved organic matter (DOM) leaching from mangrove roots and the ability of mangrove-associated sponge-bacterial consortia to degrade mangrove DOM may cause this distinction. Methods This study tested whether mangrove DOM, leaching from mimicry substrates or directly injected in sponge tissue, affected the performance of a reef and a mangrove sponge species. Results Controls and the mangrove sponge remained unaffected by mangrove DOM leaching from mimicry substrates or directly injected in sponge tissue, but the reef species showed substantial necrosis when exposed to mangrove DOM. Conclusions Results presented in this study suggest that mangrove DOM confines the composition of sponge communities in mangrove ecosystems, explaining the exclusion of typical reef species and the adjacent occurrence of distinct sponge communities.
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