Modelling the trophic roles of the demersal Chondrichthyes in the Northern Ionian Sea (Central Mediterranean Sea)

•Three mass-balance models were used to explore the trophic role of demersal chondrichthyes in the food web of the northern ionian sea.•The bathyal sharks resulted the most keystone species acting as apex predators and meso‑predators.•Demersal chondrichthyes resulted beneficial predators of lower trophic levels and some commercial species.•The trawl exerted a great indirect impact on the demersal chondrichthyes especially in coastal shelf.•The implementation of appropriate conservation measures for these top-predators is required to guarantee valuable ecosystem services. The maintenance of natural capital and the stability of regulation services of marine ecosystems has proved to be linked to the conservation of key species supporting the ecosystems function. Chondrichthyes are key top-predators and their removal from marine ecosystems due to fishing exploitation could lead to changes in species interactions and biomass that can negatively influence the provision of ecosystems services. The ecological role of the demersal Chondrichthyes living in the marine food web of the Calabrian area in the Northern Ionian Sea (Central Mediterranean Sea) was analysed by means of ecological indicators derived from Ecopath mass-balance food web models estimated in their stationary states during the periods 1995–1997, 2003–2005 and 2013–2015. The trophic web model was described by 57 functional groups (7 of which representing the demersal Chondrichthyes), which were described by their Biomass (t/km2), Production and Consumption rate, Diet, Landings (t/km2) e Discards (t/km2). Remarkable changes in biomass were recorded for shark and rays, as a consequence of changes in fishing patterns and oceanographic regime shift named Bimodal Oscillating Systems (BiOS). Demersal Chondrichthyes occupy high trophic positions in the Calabria food web showing trophic levels higher than 4.1, with the D. licha identified as the main apex predators, while E. spinax and G. melastomus as meso‑predators. The pattern of the consumption flows highlighted a potential sensitivity of E. spinax and G. melastomus to the changes in deep waters circulation caused by the BiOS acting on the entire ecosystem of the Ionian Sea. D. licha was identified as the main keystone predators in all the investigated periods. The analysis of the trophic indirect and direct impacts shows the role of the demersal Chondrichthyes as beneficial predators, with positive effects on several preys. Results also showed that G. m