Where are the jellyfish? An integrative molecular study to reveal the gelatinous zooplankton species diversity, distribution, and connectivity within a changing Southern Ocean

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Gelatinous zooplankton (GZP) are a paraphyletic and ecologically diverse planktonic group comprising cnidarian, ctenophores, and tunicates. GZP are notorious for their “jellyfish blooms”, that can have detrimental impacts on human activities at sea and on the structure of marine ecosystems. Recently, a paradigm shift has however occurred, also underlying the widespread importance and benefits of GZP, from playing a key role in the trophic pelagic web, to providing an important ecosystem service with their contribution to the carbon pump through “jelly-falls”. In the Southern Ocean (SO), environmental changes have led in some areas to an abundance shift in microzooplankton grazers from krill to salps. Besides the extensively studied salp, there is still a considerable knowledge gap on other SO GZP taxa. This knowledge gap is primarily due to traditional net surveys being unsuitable to study these fragile organisms. Therefore, the main goal of this project is to integrate molecular methodologies to characterize the species diversity, distribution, and population connectivity of SO GZP and to link these to environmental parameters. In the first objective, environmental DNA (eDNA) analyses will be used to characterize the GZP species composition and how it can be linked to different water masses. The species composition of the eDNA found in marine sediments will also be compared with those of overlaying water column, to better understand the role of GZP in the carbon pump. In a second objective, phylogeographic analyses based on sampled specimens will be employed to answer genetic diversity and connectivity questions related to SO GZP. Whether populations are circumpolar and the role of the Antarctic Polar Front against gene flow will be tested. In a third and final objective, ecological niche modelling in three dimensions will be used to model the distribution range of SO GZP and define their limiting factors. Establishing this baseline information will be crucial to predict how environmental change will affect the GZP community composition and distribution, and by consequence, how it will impact trophic networks and the SO carbon pump in the future.