Long-term biodiversity responses to anthropogenic change are spatially and taxonomically heterogeneous across coastal wetlands

Coastal wetlands in the Iberian Peninsula have experienced centuries of human impact, yet their long-term biodiversity patterns remain unclear due to limited monitoring efforts. Sedimentary ancient DNA (sedaDNA) provides a historical lens for studying how biodiversity varies across different environments and timeframes. Researchers analyzed COI and 18S sedaDNA, along with 210Pb and radiocarbon dating, sediment chemistry, and stable isotope data from eight coastal wetlands across four regions.

They examined how eukaryotic amplicon sequence variant (ASV) richness and taxonomic composition related to an Anthropogenic Enrichment Index (AEI), a measure of human activity levels.

The relationship between richness and enrichment varied among sediment samples and genetic markers. In one Cadiz site, higher enrichment led to lower biodiversity for both markers, while in the Ebro Delta, COI richness increased with enrichment. However, considering calendar time, only the positive association in the Ebro Delta remained significant, suggesting that some initial correlations were influenced by shared temporal trends.

Analyzing rolling correlations revealed that the relationship between richness and enrichment changed over time within individual sites. Taxonomic profiles differed between markers and wetlands, and community composition was distinct among sediment records, indicating ecological differences not visible through richness data alone.

The multiproxy changes followed locally specific patterns rather than a uniform regional trend. These findings demonstrate that long-term relationships between sedimentary enrichment and biodiversity are context-dependent and influenced by the chosen temporal perspective. Combining molecular, geochemical, and isotopic records enhances the historical understanding of biodiversity change and aids in developing conservation strategies that consider taxonomic composition, environmental history, and location-specific reference conditions.