Integrating Dietary Characterisation and Gut Microbiome Analysis in Norway Lobster (Nephrops norvegicus) Through Gut-Isotope-DNA (GID) Approach

Abstract The Norway lobster ( Nephrops norvegicus ) is an ecologically and commercially important species in the Mediterranean Sea and the North-East Atlantic. Therefore, studies on its trophic ecology are particularly relevant also for the purpose of sustainable management. This work aims to characterise, to the authors’ knowledge for the first time in a crustacean, both gut microbial composition and feeding ecology through Gut-Isotope-DNA (GID) approach, which integrates gut content, stable isotopes and DNA metabarcoding analyses. Specimens were collected inside and outside the Pomo Pits Fishery Restricted Area (Adriatic Sea) in 2019 and 2023, in order to assess the spatial and temporal variability in diet and microbiome. Visually identified prey were dominated by the squat lobster Iridonida speciosa , and this was also confirmed through isotopic mixing models. However, DNA metabarcoding allowed a more exhaustive reconstruction of the mixed scavenger-predator behaviour of Norway lobster, with a higher dietary diversity, and greater contribution from finfish, recorded in 2019 than 2023, both inside and outside the Pomo Pits. Gut microbiome composition followed these trophic patterns, with significantly higher microbial diversity in specimens collected outside the Pits. The microbiome was dominated by Vibrionaceae, Erysipelotrichaceae and Mycoplasmataceae, and was able to distinguish both sampling area and years more effectively than strictly dietary analyses. While dietary composition and gut microbiome structure in Norway lobster appeared consistent, each technique homes in on different biological phenomena, requiring tailored interpretations and careful consideration when integrating evidence for the purpose of management.