To evaluate the stability and resilience¹ of coastal ecosystem communities to perturbations that occurred during the Anthropocene,² pre-industrial biodiversity baselines inferred from paleoarchives are needed.^3,4 The study of ancient DNA (aDNA) from sediments (sedaDNA)⁵ has provided valuable information about past dynamics of microbial species6, 7, 8 and communities9, 10, 11, 12, 13, 14, 15, 16, 17, 18 in relation to ecosystem variations. Shifts in planktonic protist communities might significantly affect marine ecosystems through cascading effects,19, 20, 21 and therefore the analysis of this compartment is essential for the assessment of ecosystem variations. Here, sediment cores collected from different sites of the Bay of Brest (northeast Atlantic, France) allowed ca. 1,400 years of retrospective analyses of the effects of human pollution on marine protists. Comparison of sedaDNA extractions and metabarcoding analyses with different barcode regions (V4 and V7 18S rDNA) revealed that protist assemblages in ancient sediments are mainly composed of species known to produce resting stages. Heavy-metal pollution traces in sediments were ascribed to the World War II period and coincided with community shifts within dinoflagellates and stramenopiles. After the war and especially from the 1980s to 1990s, protist genera shifts followed chronic contaminations of agricultural origin. Community composition reconstruction over time showed that there was no recovery to a Middle Ages baseline composition. This demonstrates the irreversibility of the observed shifts after the cumulative effect of war and agricultural pollutions. Developing a paleoecological approach, this study highlights how human contaminations irreversibly affect marine microbial compartments, which contributes to the debate on coastal ecosystem preservation and restoration.

为了评估沿海生态系统群落¹对人类世期间发生的扰动的稳定性和复原力，需要从古档案中推断出^{2个工业前生物多样性基线。3 , 4}从沉积物中研究古 DNA (aDNA) ( sed aDNA) ⁵提供了有关微生物物种 6、7、8 和群落 9、10、11、12、13、14、15、16、17、18 与生态系统变化相关的过去动态的宝贵信息。浮游原生生物群落的变化可能会通过级联效应显着影响海洋生态系统，19、20、21，因此对该区域的分析对于评估生态系统变化至关重要。在这里，从布雷斯特湾（法国东北大西洋）的不同地点收集的沉积物核心允许约。1400 年来人类污染对海洋原生生物影响的回顾性分析。sed的比较aDNA 提取和不同条形码区域（V4 和 V7 18S rDNA）的元条形码分析表明，古代沉积物中的原生生物组合主要由已知会产生静止阶段的物种组成。沉积物中的重金属污染痕迹归因于二战时期，与甲藻和原生藻群落的变化相吻合。战后，尤其是从 1980 年代到 1990 年代，原生生物属的转变伴随着农业来源的慢性污染。随着时间的推移，社区组成重建表明没有恢复到中世纪的基线组成。这表明在战争和农业污染的累积效应之后观察到的变化是不可逆的。发展古生态学方法，