An assessment of European and Atlantic sturgeons’ paleoniches during the Holocene

The use of species distribution models (SDMs) in paleoecology enhances its contribution to ecology and conservation biology, such as estimating climate change impacts and informing conservation efforts. Acipenser sturio and A. oxyrinchus are closely related sturgeon species currently arranged in two disjunct distributions across the Atlantic Ocean. However, paleogenetic findings highlighted that both species were present in European waters over at least five millennia. Their joint European history during the Holocene period might have been driven by the thermal hypothesis, with A. oxyrinchus being a cooler-water species than A. sturio . Given their current poor state of conservation, quantifying their environmental preferences at a time when the two species were more abundant could help shape future conservation/restoration measures. Paleo-species distribution models were built for each species based on paleoclimate variables and archeozoological remains, most of which were genetically identified at the species level. Response curves for air temperature and precipitation were then applied to estimate relative continental paleohabitat suitability (HSI) in watersheds across four regions (i.e., the Baltic Sea, the Northern Seas, the South European Atlantic shelf, and the Mediterranean Sea) throughout the Holocene. The estimated niches confirmed the thermal sensitivity difference between the two species, with A. oxyrinchus having a narrower thermal range towards colder annual temperatures. Comparing HSI suitability between the two species, the four regions were globally all suitable for A. sturio but not for A. oxyrinchus , which showed much greater variability. Catchments with outlets to the Mediterranean Sea and the South European Atlantic shelf were mainly suitable for A. sturio . In contrast, those with an outlet in the Baltic Sea were slightly more suitable for A. oxyrinchus than for A. sturio . Catchments with outlets to the Northern Seas showed comparable suitability for both species. This superposition in near-past suitable habitats implied that the two species can potentially exist under the same environmental conditions and as such suggested future risks of biotic interactions which should be further acknowledged in potential stocking practices.