Laboratory studies on the biodegradation of organisms for estimating carbon storage potential in coastal aquatic ecosystems

To assess the potential as carbon storages of short-life organisms in shallow coastal areas, refractory carbon fractions were examined using rapid biodegradation experiments. Refractory fractions of primary producers, such as seaweed and phytoplankton represented 31.2%-44.0% of the total carbon content. The seagrass Zostera marina contained a high rate of refractory carbon fraction, with 83.4% of the carbon in the belowground parts of Z. marina remaining as refractory carbon, which suggested that it had a significant function as a carbon storage in the shallow coastal area. The content of refractory carbon in the soft tissues of bivalves and gastropods were approximately 8.5%-31.5%, lower than that in other macrobenthos such as arthropods and echinoderms (29.7%-52.0%). The residual carbon in mollusk shells was mostly particulate inorganic carbon. In addition, 4.0%-19.1% of refractory organic carbon derived from polysaccharides and/or proteins in biominerals, while byssus remained. Considering the amount of shells in the shallow coastal zone, this organic carbon appeared to be a substantial carbon storage. Results suggested that not only primary producers but also macrobenthos and sessile animals have important carbon storage functions in coastal aquatic ecosystems.