The decommissioning of aging oil and gas platforms and the rapid proliferation of offshore wind turbines is causing a paradigm shift in the marine energy infrastructure. Yet, limited understandings of ecological roles of these structures hinders assessments on potential ecological consequences of marine ecosystems and developing ecologically best practices in management strategies. Here, we integrate Northeast Atlantic groundfish trawl data from internationally coordinated surveys with a Bayesian Integrated Nested Laplace Approximation model to assess effects of offshore structures on fish abundance, biomass, and body size at both community and feeding-guild levels for 11,591 surveys. We then assessed scale-dependent diversity estimates by partitioning γ-diversity (regional richness) between α (local richness) and β (species turnover) and tested their responses to structure covariates in terms of the extent and scale. We found that oil and gas platforms and wind turbines altered community abundance, biomass, and body size, while environmental gradients were major drivers of ⍺–, β–, and γ–diversity. Wind turbines favoured fish at lower feeding guilds, while larger piscivores were adversely affected by structures. Overall structure effects on fish biodiversity were limited and spatially heterogeneous, while they were dominant drivers in areas with high exposure. Cumulative wind development promoted fish community reorganisation through fish feeding guild replacement. These findings demonstrate that the transition in infrastructure seascape is reshaping fish food webs and ecosystem functioning at the regional scale.