The fall of jellies: Quantifying jellyfish bloom detritus deposition on the seafloor and its effects on pelagic and benthic ecosystems

Jellyfish blooms appear to be increasing in frequency and severity across the worlds oceans, including in Norway, as a consequence of over-fishing, eutrophication, coastal development and climate change, and often bring with them substantial negative ecol ogical and economic impacts, which have been the focus of attention in numerous studies. Despite a variety of studies that have addressed the controls behind, and impact from jellyfish blooms on pelagic environments, only a few studies have assessed the impact of jellyfish detritus (carcasses/ discarded gelatinous houses) on pelagic and benthic ecosystems despite recent suggestions that impacts from the detritus could be as large as the blooms themselves, especially in poorly flushed water bodies (e.g. Norwegian fjords) that often support large populations of jellyfish. In this study, we will for the first time 1) assess the impacts of jellyfish detritus on oxygen demand and nutrient production in the water column, 2) quantify the fraction of pelagic b iomass that sinks to the seafloor and therefore the importance of gelatinous zooplankton carcasses/discards in the 'biological-pump', 3) examine scavenger biodiversity and scavenging rates of dead, low energy content jellyfish versus high energy content f ish carrion and 4) explore the impact of jellyfish detritus on benthic sedimentary ecosystem processes. Through elucidating post-bloom processes of several jellyfish species/types typically blooming/ found in Norway, hence placing them in a geographicall y relevant context for Norwegian society, the project will facilitate ongoing management efforts of coastal waters specifically and ocean systems in general and thus be of significance within existing administrative and management frameworks, both nationa lly and internationally. It will also further our understanding of marine ecosystem processes, specifically benthic-pelagic coupling in the context of geographical and species-specific variation and climate change.