Among the many research projects conducted during the B121 cruise, trophic ecology has taken an important place for divers and fish specialists all along the campaign. But what is it about ? Beyond the formal and bit severe words, trophic ecology can be simply and instinctively recapped by the famous idiom “you are what you eat” ! Every single piece of snack each of us ingests or drop of liquid we are happy to sip not only contributes to maintaining our whole body in good shape but also, and insidiously leaves its indelible mark in our organs. This holds true for all living beings and for isotopes as well ! Analyzing the composition of organisms in Carbon, Nitrogen and Sulfur stable isotopes can tell us a lot about the long story of what they usually eat and where they have been living. Eventually, analyzing the isopotic composition of organisms living in close vicinity to each other in a same place can help unreveal biological interactions between them in the food chain that is, who’s eating whom and what. That’s why specimens of some common and key species of the visited sites were sampled at the sea bottom, from seaweeds to sponges, worms, starfish, sea urchins and fish, to caracterize main food web elements and compare them between sites. The complexity of food webs is also a condition of ecosystem resilience facing climate change, the more redundant and complex biotic interactions are in a food web and the more likely the ecosystem is to resist to change. Let’s wait a bit and see what isotopes will tell … !