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Microbial Degradation of Jellyfish-Derived Substrates

Periodic Reporting for period 1 - MIDAS (Microbial Degradation of Jellyfish-Derived Substrates)

Reporting period: 2018-07-02 to 2020-07-01

The complex pool of dissolved organic matter (DOM) in the oceans is almost exclusively accessible to diverse members of microbial community carrying out different types of metabolism thereby, affecting the biogeochemical state of the ocean. To predict the response of the marine ecosystem to natural and anthropogenic perturbations, a mechanistic understanding on the relation between the organic matter (OM) field and the metabolic network operated by the microbial community needs to be refined. One largely overlooked but significant source of DOM are jellyfish. Regardless the debate over the accuracy of their reported global increase and on the true cause of the observed jellyfish fluctuations, the increase in their population size can have serious ecological and socio-economic consequences. As jellyfish blooms decay, sinking carcasses represent large quantities of detrital OM (jelly-OM), rich in proteins and hence, a high quality substrate for the ambient bacterial community. However, the exact processes and mechanisms of bacterial jelly-OM degradation remain unknown. In the MIDAS project, an integrated interdisciplinary approach was applied to characterize the composition of jelly-OM at the molecular level and the metabolic network operated by jelly-OM degrading bacterial communities using state-of-the-art analytical tools and cutting edge –omics techniques.
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.
The increase in jellyfish populations is most likely a symptom of cumulative deterioration of marine ecosystems possibly as a consequence of the combined effects of multiple anthropogenic stressors and/or climate change. The environmental consequences of jellyfish blooms and their impact on some ecosystem services have been demonstrated in several marine areas worldwide during the last decades. Beside ecological consequences, jellyfish blooms can have also a detrimental socio-economic impact on human wellbeing, representing threats to human health due to stinging, by blocking cooling intakes of coastal industry, power plants, desalinization plants, interfering with ship operations, affecting fishing industry, aquaculture by causing damage to farmed fish and acting as vectors of fish pathogens and by reducing commercial fish via predation and competition. Therefore, by investigating the jellyfish blooms’ related issues this project has the potential to be of great interest to the general public. The outcomes of this project have the potential to contribute to the solution of some of the issues associated with jellyfish blooms on the human wellbeing.
The MIDAS project - Conceptual Figure