# Past trajectory of a socio-ecosystem at the land-sea interface: the case of the northern watersheds of the Bay of Brest over the last 150 years

Clara Valero, Aurelie Penaud, Muriel Vidal, Sabine Schmidt, Pierre-Antoine

Dessandier, Evelyne Goubert, Erwan Glemarec, Pierre Brigode, Lucas

Bosseboeuf, Yves-Marie Paulet, et al.

► To cite this version:

Clara Valero, Aurelie Penaud, Muriel Vidal, Sabine Schmidt, Pierre-Antoine Dessandier, et al. Past trajectory of a socio-ecosystem at the land-sea interface: the case of the northern watersheds of the Bay of Brest over the last 150 years. European Geosciences Union General Assembly 2025 (EGU25), Copernicus Meetings, Apr 2025, Vienna, Austria. pp.EGU25-17787, 10.5194/egusphere-egu25-17787 hal-05051354

HAL Id: hal-05051354

https://hal.science/hal-05051354v1

Submitted on 6 Jan 2026

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# Past trajectory of a socio-ecosystem at the land-sea interface: the case of the northern watersheds of the Bay of Brest over the last 150 years

Clara Valero<fnref n="1" />, Aurelie Penaud<fnref n="1" />, Muriel Vidal<fnref n="1" />, Sabine Schmidt<fnref n="2" />, Pierre-Antoine Dessandier<fnref n="3" />, Evelyne Goubert<fnref n="4" />, Erwan Glemarec<fnref n="5" />, Pierre Brigode<fnref n="6" />, Lucas Bosseboeuf<fnref n="7" />, Yves-Marie Paulet<fnref n="7" />, Céline Liorzou<fnref n="1" />, Sidonie Revillon<fnref n="8" />, Ndèye Coumba Niass<fnref n="9" />, Pierre Ailliot<fnref n="9" />, Jean-Marc Derrien<fnref n="9" />, Clément Lambert<fnref n="4" />, and Raffaele Siano<fnref n="10" />

The Bay of Brest (BB) is a macro-tidal estuarine environment that has been exposed to strong anthropogenic pressures over the last decades, especially after the Second World War. It is therefore considered as a regional pilot site for addressing coastal ecosystem transformations since the Industrial Revolution. We analysed 4 sediment cores collected in 2 different BB areas more or less exposed to marine hydrodynamic processes: i) Elorn sector (3 cores) and ii) Bay of Daoulas (1 core), in the inner BB, close to the mouth of the Daoulas river, with the aim of deciphering past environmental changes at a high temporal resolution (sub-decadal) over the last 150 years.

Working at a local spatial scale (BB) allows addressing robust correlations between driving forces and environmental changes, as previously demonstrated by pluridisciplinary approaches in the study area (Lambert et al., 2018; Siano et al., 2021). In this project, we are therefore building on this existing dataset (low resolution palynology on the Daoulas core and sedaDNA analyses in the 4 study cores) with the addition of new analyses (high resolution palynology in the Daoulas core and new data for the others, benthic foraminiferal assemblages, sedimentological data and ICP-AES elemental geochemistry in the Daoulas core), with a very fine study resolution (2-year resolution for the Daoulas and 2 to 16-year resolution for the others). Furthermore, statistical analyses based on paleoecological time series allow the detection of major break points, especially thanks to the palynological and sedimentological datasets.

<footnote n="1">¹Geo-Ocean, Univ Brest, Univ Bretagne Sud, CNRS, Ifremer, UMR6538, IUEM, F-29280 Plouzané, France</footnote>

<footnote n="2">²Univ Bordeaux, CNRS, Bordeaux INP, EPOC, UMR 5805, F-33600 Pessac, France</footnote>

<footnote n="3">³Ifremer, BEEP, Univ Brest, F-29280 Plouzané, France</footnote>

<footnote n="4">⁴Geo-Ocean, Univ Bretagne Sud, Univ Brest, CNRS, Ifremer, UMR6538, F-56000 Vannes, France</footnote>

<footnote n="5">⁵Laboratoire Géoarchitecture, Univ Brest, F-29200 Brest, France</footnote>

<footnote n="6">⁶Univ Rennes, CNRS, Géosciences Rennes, UMR 6118, F-35000 Rennes, France</footnote>

<footnote n="7">⁷Laboratoire des Sciences de l'Environnement Marin, LEMAR, IUEM, Univ Brest, UMR6539, F-29280 Plouzané, France</footnote>

<footnote n="8">⁸SEDISOR/Geo-Ocean, Univ Brest, CNRS, Ifremer, UM 6538, IUEM, F-29280 Plouzané, France</footnote>

<footnote n="9">⁹Laboratoire de Mathematiques de Bretagne Atlantique, Univ. Brest, UMR CNRS 6205, F-29200 Brest, France</footnote>

<footnote n="10">¹⁰Ifremer, DYNECO PELAGOS, F-29280 Plouzané, France</footnote>
This work then highlights 3 major thresholds (1945, 1960-170, 1980) allowing discussion of past
changes in protist communities and in BB landscapes through time. These data are finally
discussed in the light of reanalysis of regional precipitation signals (by modelling approaches
based on NOAA data), instrumental data (nutrient concentrations) as well as historical chronicles
(land-use practices and industrial-mining-war pressures) to tackle the main forcing factors
responsible for coastal ecosystem transformations. We especially highlight the strong pressure of
agriculture practices on trophic changes and degradation of BB's water quality, as observed
through coastal observatory series (IUEM, REPHY) with the recrudescence of toxic algal blooms
since the 1980's.