The Venus nux association during the Early Pleistocene of the Adriatic Sea: a comparative analysis with its Pliocene and Recent distribution

Interplay between environmental drivers and antagonistic biotic interactions shape the niche of species. Understanding the extent to which species retain parameters of their ecological niches amid long-term environmental changes is crucial for numerous palaeoecological inferences applicable to conservation efforts, sequence stratigraphic reconstructions, and macroevolutionary theory. 

The Venus nux association of the Arda and Stirone River sections (Early Pleistocene, western Emilia, northern Italy) has been here analyzed from a systematic and a paleoecological point of view, resulting in the identification of 23 mollusc taxa. As the majority of the retrieved taxa is represented by living species, a comparison between their fossil and present-day environment has been carried out, focusing also on the Venus nux association during the Pliocene of the same region. This research aimed to assess whether the overall bathymetric range and dominance of the bivalve Venus nux have changed over the last 5 million years in the Adriatic basin. Preliminary results indicate a shift in the ecological niche of this common species during a time marked by increasingly pronounced climatic oscillations.

Indeed, currently, V. nux is rarely retrieved in the Adriatic basin, but it is common in the Alboran Sea and the Ibero-Moroccan Gulf (southern Spain), where it thrives in muddy to muddy-sandy substrates at depths between 30 and 350 meters (Salas, 1996), but typically is abundant within 60 and 120 m depth ranges. Conversely, during the Pliocene and Pleistocene geological intervals, V. nux was common in the sedimentary successions of the Adriatic Basin, though it exhibited dominance at different depths and a potentially different bathymetric range. Specimens of V. nux from the Lower Pleistocene Arda and Stirone River sections reveal a shallower bathymetric distribution (20-40 meters of water depth), as evidenced by the co-occurrence in the mollusc association of shallow-water species, like Mytilus edulis and Ostrea edulis. During the warm Pliocene (Zanclean-Piacenzian transition), its bathymetric distribution was slightly deeper than in the cold Early Pleistocene, possibly mirroring current conditions. Although further detailed studies are necessary, it seems that over the past few million years, this species has changed its niche parameters, possibly due to climate shifts.

 

 

Salas, C. 1996. Marine bivalves from off the southern Iberian Peninsula collected by the Balgim and Fauna 1 expeditions. Haliotis 25: 33–100.