Understanding the architecture of marine food webs and the diverse patterns of trophic controls is fundamental to assessing ecosystem functioning. Energy pathways are mediated by complex combinations of top-down, bottom-up and wasp-waist controls and quantifying the relative contribution of direct and indirect interactions played by species (or trophic groups) is a critical challenge. This contribution provides a preliminary quantitative assessment of trophic control patterns and direct and indirect impacts played by key species within the food web of the Northern Ionian Sea (NIS, Central Mediterranean Sea).

An Ecopath trophodynamic model was developed for the NIS food web, described by 64 functional groups (FGs) for the 2008-2010 period. The model integrated inputs for each FG, including biomass (ton/km²), production and consumption rates (year^-1), diets (W%), gear-specific landing and discard (ton/km²). For FGs identified by keystoneness indices, a novel breakdown analysis based on the Mixed Trophic Impact matrix was applied with Trophic Level (TL) Decomposition routine across integer TLs.

The food web was organized across five integer TLs, with odontocetes occupying the highest trophic position. High-TL predators displayed two distinct top-down cascading patterns: pelagic apex consumers (e.g. striped dolphin) propagated positive indirect effects down to TLII via competitor removal and mesopredator release, whereas demersal top predators, such  as anglers, exhibited high negative impacts mostly on TLIV. Squids and mesopelagic fishes functioned as wasp-waist regulators, supporting the benthic-pelagic coupling. Conversely, zooplankton and benthic macroinvertebrates exerted predominant bottom-up control that progressively attenuated starting from TL>3.5. The analysis estimated a 58% contribution of indirect trophic impacts across the food web, mostly represented by the removal of competitors by keystone FGs. By capturing non-linear pathways and identifying key groups, this multi-level decomposition provides quantitative metrics to assess trophic controls patterns, and the methodology could be applied to assess the indirect fishing impacts on the food web.