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

胶状浮游动物（GZP）包括远洋栉水母、刺胞动物和海带被认为是气候变化的赢家。在世界各地的一些海洋生态系统中，近几十年来它们的数量显著增加。这种所谓的“水母化”也适用于南大洋变暖地区，其生态系统从以磷虾为基础的生态系统转变为以海带为基础的生态系统。除了海鞘外，其他南极凝胶状浮游动物几乎没有被研究过，因为这种难以捉摸的远洋领域的组成部分由于传统的网状取样的人工制品而无法检测到，忽略了GZP的多样性并低估了它们的丰度。考虑到GZP构成了远洋生物量的很大一部分，并且将变得更加重要，它们作为猎物的生态系统影响可能同样增加。直到最近，GZP还被认为是一个“营养死胡同”。这种偏颇的观点认为，它起源于对GZP的水状软组织的快速消化，使它们在捕食者的胃中“看不见”，这是传统显微镜观察的结果，就像许多浮游生物样本“看不见”一样。然而，新的研究表明，在整个世界海洋中，许多分类群经常消耗GZP。在这里，我们想验证这种模式的转变，为南大洋的上层和底层生态系统。为此，我们将采用DNA元条形码方法研究片足类动物和鱼类的食性组成和GZP捕食的时空变化。随后，基于用这种方法和生物信息学去噪获得的数百万条DNA reads，我们希望进行一项metaphylogeography研究。通过这种方法，我们的目的是探索难以取样的凝胶状浮游动物物种的遗传结构和种群连通性。

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.