In the MIDAS project we have scaled the characterization of the detrital OM of two different cosmopolitan jellyfish species down to the individual compound level, i.e. the scale relevant for microbially mediated biochemical reactions. We show that about half of the detrital jelly-OM is instantly available as DOM and thus, exclusively and readily accessible to microbes. The composition of jellyfish detritus indicates that it represents a high quality and easily degradable substrate for heterotrophic marine bacteria that could become available to ambient water microbial communities in large quantities at the demise of jellyfish blooms. In fact, our results revealed that essentially the entire labile jelly-OM is rapidly degraded by a simple consortium of bacteria, exhibiting unique metabolic features and complex interspecies interactions. This simple bacterial consortium accounted for > 90% of all metabolically active jelly-OM degraders, exhibiting high bacterial growth efficiencies. This implies that a major fraction of the detrital jelly-OM is rapidly degraded and incorporated into biomass by opportunistic bacteria, with important implications for the structure and functioning of marine ecosystems. We estimate that about half of detrital jelly-OM is remineralized by planktonic bacteria in the water column. This implies that the amount of jelly-OM reaching the seafloor is effectively reduced by microbial processing of jelly-OM in the water column. This has important implications for the fate and flux of jellyfish-derived OM in the ocean. Microbial processing of jelly-OM results in the accumulation of inorganic nutrients, with possible implications for the biogeochemical state of the marine ecosystem. In addition, the increase of the concentrations of major inorganic nutrients after a decay of jellyfish blooms in coastal waters might lead to nuisance phytoplankton blooms in coastal waters. In this way, the MIDAS project provided new insights into the cycling and fate of this jelly-OM pool in the ocean. The knowledge obtained within the MIDAS project will enable us understanding the implications of jellyfish blooms on biogeochemical cycles in coastal seas.
The outcomes of the MIDAS project are of interest for the broader scientific community, in particular to different areas of marine research. In this regard, the outcomes of the project were disseminated at the Symposium of Aquatic Microbial Ecology (SAME) 16 at Potsdam, Germany, and at the Science Talk event organized by University of Vienna, Austria in 2019. Moreover, the outcomes of the project have the potential to be used by the innovative research sector, blue economy promoters and agents and were as such promoted at the competition Falling Walls Lab -MSCA Actions, organized within European Research & Innovation Days in Brussels, Belgium in 2019.
