Abundance of Cnidaria and Ctenophora taxa in the North Atlantic sampled during the G. O. Sars Cruise in May 2013

In recent years a global increase in jellyfish (i.e. Cnidarians and Ctenophores) abundance and a rise in the recurrence of jellyfish outbreak events have been largely debated, but a general consensus on this matter has not been achieved yet. Within this debate, it has been generally recognized that there is a lack of reliable data that could be analyzed and compared to clarify whether indeed jellyfish are increasing throughout the world ocean as a consequence of anthropogenic impact and hydroclimatic variability. During the G.O. Sars cruise jellyfish were collected at different depths in the 0-1000m layer using a standard 1 m**2 Multiple Opening/Closing Net and Environmental Sensing System (MOCNESS) (quantitative data), Harstad and macroplankton trawls (qualitative data). The comparison of records collected with different nets during the G.O. Sars transatlantic cruise shows that different sampling gears might provide very different information on jellyfish diversity. Indeed, the big trawls mostly collect relatively large scyphozoan and hydrozoan species such as Atolla, Pelagia, Praya, Vogtia, while small hydrozoans (e.g. Clytia, Gilia, Muggiaea) and early stages of ctenophora are only caught by the smaller nets.

近年来，全球范围内水母（即刺胞动物门（Cnidarians）与栉水母动物门（Ctenophores））丰度的提升，以及水母暴发事件频发程度的加剧，已成为学界广泛讨论的焦点议题，但目前尚未就该问题达成普遍共识。在这场学术讨论中，学界普遍认可当前缺乏可供分析与对比的可靠数据，无法厘清全球海洋中的水母丰度是否确实因人类活动影响及水文气候变异而呈上升趋势。在G.O.萨尔兹（G.O. Sars）科考航次中，研究人员采用标准1平方米多网分层开闭网与环境感知系统（Multiple Opening/Closing Net and Environmental Sensing System, MOCNESS）采集定量数据，同时使用Harstad拖网与大型浮游生物拖网采集定性数据，于0-1000米水层的不同深度收集了水母样本。通过对G.O.萨尔兹跨大西洋航次中不同网具采集的记录开展对比分析可知，不同采样设备所获取的水母多样性信息可能存在显著差异。具体而言，大型拖网主要捕获体型相对较大的钵水母纲（Scyphozoa）和水螅纲（Hydrozoa）物种，如发冠水母属（Atolla）、霞水母属（Pelagia）、管水母属（Praya）、沃格特水母属（Vogtia）等；而小型水螅类（如克里昂水母属（Clytia）、吉利亚水母属（Gilia）、穆格水母属（Muggiaea））以及栉水母动物的幼体阶段，仅能通过小型网具捕获。