Sight unseen: Elucidating the trophic role and metapopulation structure of Southern Ocean gelatinous zooplankton using DNA metabarcoding

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Gelatinous zooplankton (GZP) including pelagic ctenophores, cnidarians and salps are reputed to be climate change winners. In several marine ecosystems worldwide, they significantly increased in numbers over recent decades. This so-called “jellification” also holds for the warming region of Southern Ocean, with its notorious shift from a krill-based to a salp-based ecosystem. Besides salps, other Antarctic gelatinous zooplankton are barely studied, since this elusive component of the pelagic realm remained undetectable due to artefacts of traditional net sampling, overlooking GZP diversity and underestimating their abundances. Considering that GZP compose a large fraction of the pelagic biomass and will become even more central, their ecosystem impact as prey may similarly increase. Until recently, GZP were considered as a “trophic dead end”. This biased view finds it origin in the rapid digestion of the watery, soft tissues of GZP, making them “invisible” in predators’ stomachs for traditional microscopy, in the same way many are “invisible” in plankton samples. However, new approaches have shown that many taxa routinely consume GZP throughout the World Ocean. Here, we want to validate this paradigm shift for Southern Ocean pelagic and demersal ecosystems. To do so, we will investigate the spatio-temporal variation in diet composition and the occurrence of GZP predation for amphipod and fish species using a DNA metabarcoding approach. Subsequently, based on the millions of DNA reads obtained with this method and bioinformatic denoising, we want to conduct a metaphylogeographic study. By this, we aim to explore the genetic structure and population connectivity of the otherwise difficult to sample gelatinous zooplankton species.