Financeur du programme

programme national
ISblue

Résumé

Do ancient protist community shifts coincide with hydrological perturbations of the BoB (e.g. fluvial and hydrodynamic processes, temperature and salinity changes, nutrient fluxes, eutrophication, and pollution)? Are the observed biological changes synchronous at the macro-scale of the BoB (Elorn versus Aulne watershed)?

Dinocyst assemblages, concentrations, fluxes and diversity indexes will be conducted on all available cores. PACTE will deliver a synthesis on both “traditional” (palynology) and “innovative” (DNA in ancient sediments) approaches based on the corpus of acquired paleoecological information. In addition, current monitoring for pollen grains (Objectif Plancton samples and Lanvéoc Somlit-station) will be conducted for dinocysts.

The assemblages of diatoms, marine organisms composed of intricate silica (SiO₂) skeletons, are very sensitive to environmental changes. Diatom species assemblages, biogenic silica (bSiO₂; wet alkaline digestion) and total Si (HF digestion) will be analysed on PACTE cores. This will enable the quantification of the ratio bSiO₂ versus total Si as a proxy for land-use change.

Foraminifera are unicellular eukaryotes, which can produce skeletons of calcium carbonate (CaCO₃) or agglutinated (chitinous organic matter and mineral grains). Assemblages of benthic species are associated with particular environmental conditions, depending on different parameter fluctuations as dissolved oxygen, organic matter, potentially toxic elements, salinities, or suspended matter load. Benthic foraminiferal assemblages, concentrations, fluxes and diversity indexes will be conducted on PACTE cores. In addition, other parameters (e.g. clustering for the identification of ecological groups, rank/frequency analysis, rates of morphological abnormalities) can be reconstructed to identify different drivers (natural or anthropogenic) and to specify deterioration/restoration phases.

Metabarcoding (analysis of barcode gene of taxonomic diversity) of sedaDNA will allow biodiversity analyses of protist paleocommunities on the new core collected at the Aulne River mouth. Metagenomic analyses (analysis of barcode gene of functional diversity) on sedaDNA will be performed on the new collected core to test whether human pollution caused the emergence of new functional community (i.e. heterotrophs vs. autotrophs). Paleo-genomics data will be calibrated in time and compared to contemporary environmental data to assess: i) shifts in plankton community diversity and their anthropogenic drivers, ii) the emergence of novel functional biodiversity traits following ecosystem variations, iii) long-term dynamics of invasive species and biodiversity decline. Paleogenetic analyses in the BoB will be contextualised in the framework of the TREC expedition (TRaversing European Coastline, 2023-2024) led by EMBL and co-organised with Tara Foundation, Ifremer and EMBRC during which about 30 cores will be collected in polluted (industrial, agricultural and WWII impacted sites) and pristine European coastal sites. This comparison will allow understanding if pollution-driven biological shifts observed in the BoB are a common or unique pattern in the European context across the last centuries.

Statistical analyses will be conducted for the detection of tipping points in paleoecological data with the LMBA.