The role of glass sponge reefs in nutrient cycling: inputs, outputs, and evidence of population changes through the millennia

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Glass sponges form dense reefs covering hundreds of kilometers of seafloor in the shallow waters of British Columbia. The sponges provide a unique habitat for commercially important rockfishes, but their role in local biogeochemical cycling has not yet been explored. The reefs are under consideration for protection from trawling and other fishing operations, but their role as sources of carbon (food) and silicon (skeletal material) for other less productive habitats nearby may be of equal if not greater importance. In the proposed work, a sponge "carbon signature" will be traced downstream of the reefs using fatty acid and stable isotope analyses from sediment traps, cores, water samples, and sponge samples. This signature will be used to trace carbon inputs into the reefs and the fate of that carbon once it is processed by the sponges. Rates of silicon uptake, which have historically been below detection limits of current methods, will be integrated over time using a novel method involving the dye PDMPO to mark growth rings in spicules. Finally, the robustness and extent of these reefs will be examined using sediment cores collected around British Columbia by the Integrated Ocean Drilling Program. Combining the different approaches and novel methods proposed here will provide a clear picture of the role sponge reefs play in carbon and silicon cycling and will help inform policymakers for decisions on future marine protected areas.