Sediment archives reveal irreversible shifts in plankton communities after World War II and agricultural pollution

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.

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Document S1. Figures S1–S4 and Tables S1 and S2.
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Data S1. Dating of Elorn Estuary (EE), Daoulas Estuary (DE), and Brest Harbor (BH) cores, related to STAR Methods. (A) Elorn Estuary (EE) sediment chronology. (B) Daoulas Estuary (DE) sediment...
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Data S2. Taxa known to form resting stages , related to STAR Methods. (A) V7 barcode. (B) V4 barcode.
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Document S2. Article plus supplemental information.
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Siano Raffaele, Lassudrie Duchesne Malwenn, Cuzin Pierre, Briant Nicolas, Loizeau Veronique, Schmidt Sabine, Ehrhold Axel, Mertens Kenneth, Lambert Clément, Quintric Laure, Noël Cyril, Latimier Marie, Quéré Julien, Durand Patrick, Penaud Aurélie (2021). Sediment archives reveal irreversible shifts in plankton communities after World War II and agricultural pollution. Current Biology. 31 (12). 2682-2689.e7.,

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