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.

Members of the Daphnia longispina O. F. Müller, 1776 group (Branchiopoda: Cladocera) are keystone grazers in freshwater bodies around the world. Multiple cryptic species have been revealed and partially described within the last 20 years. However, high phenotypic plasticity, hybridization, and the limited number of available genetic markers have hampered attempts to fully explore species diversity and speciation factors in this group. Here, we present the first dated phylogeny of the complete D. longispina group using whole-genome data. Multiple mitochondrial relationships including divergent mitochondrial lineages are not supported by nuclear DNA. Additionally, several morphologically distinct species within two species complexes show a low genealogical divergence index, raising the question of lumping by the method. Species trees based on SNPs and gene trees differ strongly in bootstrap support for older nodes. Concordance factors do not strongly support either phylogeny, most likely due to prevalent incomplete lineage sorting. Our analyses indicate that geography has a stronger effect on the speciation of the D. longispina group than the trophic status of their habitat or introgression. We only find evidence of ancient introgression between species known to hybridize concurrently. This study provides novel insights into the species relationships in the D. longispina group.

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.