The PEACETIME cruise (May–June 2017) was a basin-scale survey covering the Provencal, Algerian, Tyrrhenian, and Ionian basins during the post-spring bloom period and was dedicated to tracking the impact of Saharan dust deposition events on the Mediterranean Sea pelagic ecosystem. Two such events occurred during this period, and the cruise strategy allowed for the study of the initial phase of the ecosystem response to one dust event in the Algerian Basin (during 5 d at the so-called “FAST long-duration station”) as well as the study of a latter response to another dust event in the Tyrrhenian Basin (by sampling from 5 to 12 d after the deposition). This paper documents the structural and functional patterns of the zooplankton component during this survey, including their responses to these two dust events. The mesozooplankton were sampled at 12 stations using nets with two different mesh sizes (100 and 200 µm) that were mounted on a Bongo frame for vertical hauls within the depth layer from 0 to 300 m. The Algerian and Tyrrhenian basins were found to be quite similar in terms of hydrological and biological variables, which clearly differentiated them from the northern Provencal Basin and the eastern Ionian Basin. In general, total mesozooplankton showed reduced variations in abundance and biomass values over the whole area, with a noticeable contribution from the small size fraction (<500 µm) of up to 50 % with respect to abundance and 25 % with respect to biomass. This small size fraction makes a significant contribution (15 %–21 %) to the mesozooplankton fluxes (carbon demand, grazing pressure, respiration, and excretion), which is estimated using allometric relationships to the mesozooplankton size spectrum at all stations. The taxonomic structure was dominated by copepods, mainly cyclopoid and calanoid copepods, and was completed by appendicularians, ostracods, and chaetognaths. Zooplankton taxa assemblages, analyzed using multivariate analysis and rank frequency diagrams, slightly differed between basins, which is in agreement with recently proposed Mediterranean regional patterns. However, the strongest changes in the zooplankton community were linked to the abovementioned dust deposition events. A synoptic analysis of the two dust events observed in the Tyrrhenian and Algerian basins, based on the rank frequency diagrams and a derived index proposed by Mouillot and Lepretre (2000), delivered a conceptual model of a virtual time series of the zooplankton community responses after a dust deposition event. The initial phase before the deposition event (state 0) was dominated by small-sized cells consumed by their typical zooplankton filter feeders (small copepods and appendicularians). The disturbed phase during the first 5 d following the deposition event (state 1) then induced a strong increase in filter feeders and grazers of larger cells as well as the progressive attraction of carnivorous species, leading to a sharp increase in the zooplankton distribution index. Afterward, this index progressively decreased from day 5 to day 12 following the event, highlighting a diversification of the community (state 2). A 3-week delay was estimated for the index to return to its initial value, potentially indicating the recovery time of a Mediterranean zooplankton community after a dust event. To our knowledge, PEACETIME is the first in situ study that has allowed for the observation of mesozooplankton responses before and soon after natural Saharan dust depositions. The change in the rank frequency diagrams of the zooplankton taxonomic structure is an interesting tool to highlight short-term responses of zooplankton to episodic dust deposition events. Obviously dust-stimulated pelagic productivity impacts up to mesozooplankton in terms of strong but short changes in taxa assemblages and trophic structure, with potential implications for oligotrophic systems such as the Mediterranean Sea.

中文翻译：

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地中海春季PEACETIME游轮上表皮中层浮游生物的结构，功能及其对尘埃沉积事件的响应

PEACETIME巡游（2017年5月至2017年6月）是一项盆地规模的调查，涵盖了春季开花后时期的普罗旺斯，阿尔及利亚，第勒尼安和爱奥尼亚海盆地，并致力于追踪撒哈拉沙尘沉积事件对地中海中上层的影响生态系统。在此期间发生了两次这样的事件，巡航策略允许研究生态系统对阿尔及利亚盆地一次尘埃事件的响应的初始阶段（在所谓的“ FAST长持续时间站”的5天期间），以及对第勒尼安盆地另一个尘埃事件的后一种响应的研究（通过在沉积后5到12 d采样）。本文记录了这次调查期间浮游动物组成部分的结构和功能模式，包括它们对这两个沙尘事件的响应。 （ μm），安装在Bongo框架上，用于从0到300 m的深度层内垂直拖拉。在水文和生物变量方面，阿尔及利亚和第勒尼安河流域被认为是非常相似的，这清楚地将它们与普罗旺斯北部盆地和爱奥尼亚东部盆地区分开来。总的来说，总中生浮游生物在整个区域内的丰度和生物量值变化减小，小尺寸部分（< 500  µm）相对于丰度最高为50％，相对于生物质最高为25％。这个很小的比例对中层浮游生物通量（碳需求，放牧压力，呼吸和排泄）做出了重大贡献（15％–21％），这是通过与所有站点中层浮游生物尺寸谱的异形关系估算的。分类学结构以co足类动物为主，主要是摆线足和类颅骨co足动物，并由阑尾虫，成骨纲和cha足纲动物完成。使用多变量分析和等级频率图分析的浮游动物分类群在各流域之间略有不同，这与最近提出的地中海区域模式相符。然而，浮游动物群落中最强烈的变化与上述尘埃沉积事件有关。根据排名频率图和Mouillot和Lepretre（2000）提出的推导指标，对第勒尼安和阿尔及利亚流域观测到的两个沙尘事件进行了概要分析，提供了浮游动物群落响应后虚拟时间序列的概念模型。灰尘沉积事件。沉积事件之前的初始阶段（状态0）主要由小型浮游动物滤食器（小型co足动物和阑尾动物）消耗的小细胞所控制。沉积事件后的第一个5 d（状态1）期间的扰动阶段随后导致较大细胞的滤食器和放牧者的强烈增加，以及食肉物种的逐渐吸引，从而导致浮游动物分布指数急剧增加。之后，该指数从事件发生后的第5天到第12天逐渐降低，突显了社区的多元化（状态2）。估计该指数要延迟3周才能恢复到其初始值，这可能表明发生尘埃事件后地中海浮游动物群落的恢复时间。 据我们所知，PEACETIME是第一个原位研究，它可以观察到撒哈拉自然粉尘沉积前后的中生浮游生物反应。浮游生物分类结构的等级频率图的变化是一个有趣的工具，可以突出浮游动物对偶发性粉尘沉积事件的短期响应。显然，受粉尘刺激的浮游生产力影响到中层浮游生物，这主要是由于分类单元和营养层结构的强而短的变化，对地中海等贫营养系统具有潜在的影响。