Département Ecologie aquatique

Seafloors are crucial to marine ecosystems for the functions and services they provide. Benthic organisms, vital to these ecosystems, are particularly vulnerable to climate change. Rising temperatures, ocean acidification, and shifting currents disrupt benthic species and communities, yet future related impact assessments remain limited. Here, we trained species distribution models with predictors from state of the art physical and biogeochemical marine models and a large database of species records (> 100,000 occurrences) to project the current and future distributions of ~350 benthic species (excluding cephalopods, invasive species, and commercially exploited species) and their related changes per site in diversity (α-) and community composition (β-diversity) over the Mediterranean Sea. We predicted most species to shift their distribution northwards for all future scenarios due to changes in water temperature and dissolved oxygen close to the seafloor, with up to 60% of species experiencing range contraction, 77% moving northwards, 20% experiencing range fragmentation (measured as range disjunctions in models' output), and 30% moving toward deeper waters over time. Cold-adapted species were more likely to face range contraction and shifts towards deeper waters, while warm-adapted species were more likely to face range expansions and shifts towards shallower waters. α-diversity increased in the Northern and decreased in the Southern Mediterranean, respectively. Changes in β-diversity within sites highlighted compositional changes (species turnover) in communities located in the Aegean and Tyrrhenian Seas, in deep parts of the Ionian Sea, and in coastal regions of the Adriatic Sea. Climate-smart, ecosystem-based Marine Spatial Planning can capitalize on the identified hotspots of species losses, gains, stability, and turnover. Prioritizing connectivity in regions of strong turnover and extending protected areas in regions with stable α-diversity and limited turnover is recommended for improved conservation actions.

Area-based conservation remains the principal strategy for preserving biodiversity, yet current planning approaches inadequately consider two critical uncertainties: future trajectories of socio-environmental drivers of environmental degradation and preferences for alternate conservation objectives. This study demonstrates how spatial conservation prioritization can be integrated with scenario-based simulation modelling to systematically evaluate conservation strategies under these uncertainties. We simulated conservation area expansion strategies (e.g. timing and extent of interventions) in Switzerland (2020-2060) using a comprehensive full-factorial design testing approaches across five scenarios of climate change, land-use change, and conservation priorities, with strategy robustness assessed through impacts on ten ecosystem services (ES) characterized across both space and time. Results revealed substantial variation in ES provision under alternative futures, with pronounced spatial shifts in service delivery. Critically, only limited spatial overlap existed between regions displaying the highest ES robustness and areas prioritized for protection based on current ecological value, demonstrating the inadequacy of planning approaches that ignore future uncertainties. The most consistently robust strategy for securing ES provision involved rapidly expanding conservation areas to 30% coverage (aligned with the Kunming-Montreal Global Biodiversity Framework target), prioritizing small patches in human-dominated landscapes, and employing mixed management combining both preservation and restoration. However, strategy effectiveness varied across different ES and scenarios, indicating that optimal approaches must account for societal preferences regarding trade-offs between services. This research addresses a recognized gap in conservation planning science and provides both methodological guidance for uncertainty-informed planning and specific recommendations for Switzerland's pursuit of the 30x30 target under accelerating environmental change.

Accurate information on species abundances and their distribution in space is key to ecological research and essential for informed decision-making in environmental management. Environmental DNA (eDNA) allows community-wide detection of biodiversity, but its limited ability to estimate species abundance from metabarcoding outputs poses important challenges for its broader application. The eDNA Integrating Transport and Hydrology (eDITH) framework addresses some of these limitations by partly accounting for eDNA transport and decay dynamics in river networks and allows predicting the spatial distribution of taxa at high resolution. However, its capability for providing quantitative estimates of taxon abundances has so far not been empirically validated. Here, we utilized spatially replicated eDNA and kick-net samples collected in spring and summer at 25 sites along a 126 km² river catchment. We contrasted species-level relative abundances of insect communities obtained via eDNA metabarcoding read counts and via eDITH estimates with those obtained from the kick-net samples. We found that eDNA read counts of sampled locations did not correlate with the associated local kick-net (i.e., realized) insect abundance, but that the eDITH estimates did. However, results varied across insect orders and the improvements provided by eDITH were highly species-specific. Our findings corroborate the inadequacy of utilizing raw read counts for quantitative inference and pose forward the potential of the eDITH framework in circumventing some of the limitations of metabarcoding outputs. Together with other recently proposed correction approaches, this framework contributes to ongoing efforts to refine the interpretability of metabarcoding data. As the demand for quantitative biodiversity data continues to grow in both ecological research and environmental management, refining and validating sampling approaches remains a critical priority.