Organic matter release by the benthic upside-down jellyfish Cassiopea sp. fuels pelagic food webs in coral reefs

Recent studies have demonstrated that organic matter released by hermatypic corals can play an important role as carrier of energy, thereby initiating element cycles in coral reef systems. However, although another commonly occurring cnidarian, the scyphozoan upside-down jellyfish Cassiopea sp., can reach high abundances in such reef systems, its potential contribution to cycles of matter remains unresolved. Therefore this study aimed to quantify organic matter release by Cassiopea from the Northern Red Sea and evaluate whether this material is transferred to planktonic microbes and zooplankton. Mean mucoid particulate organic matter release was 21.2 ± 9.4 mg POC and 2.3 ± 1.1 PN m− 2 jellyfish surface area h− 1, which exceeds release rates reported for hermatypic corals by factors of 2 to 15. Labelling experiments using stable N isotopes demonstrated uptake of Cassiopea-derived organic matter by the jellyfish-associated zooplanktonic mysids Idiomysis tsurnamali. Incubation experiments revealed that O2 consumptions by microbes and zooplankton were 5.9- and 3.8-fold higher compared to seawater controls, respectively, when Cassiopea-derived organic matter was present. Total organic carbon (TOC) degradation rates increased 5.0-fold (0.27% h− 1 versus 1.38% h− 1), thereby indicating fast mineralization of Cassiopea-derived organic matter. These findings suggest that Cassiopea-derived organic matter may function as a newly discovered trophic pathway for organic matter from the benthic environment to pelagic food chains in coral reefs and other marine ecosystems.