IDENTIFYING THE MAIN STRUCTURE OF BENTHIC TROPHIC NETWORKS IS NECESSARY TO UNDERSTAND THE FUNCTIONING OF MARINE COMMUNITIES. FOR THAT PURPOSE, THE TRAINEE WILL ANALYSE NATURAL ¹³C AND ¹⁵N STABLE ISOTOPES AND FATTY ACID BIOMARKERS ON ECHINOID SPECIMENS TO ALLOW DISCRIMINATING AMONG THE FOOD SOURCES OF TARGET SPECIES, THE MEAN/BROAD POSITION OF THE TARGET SPECIES IN THE TROPHIC NETWORKS (FEEDING STRATEGIES), AND THE TROPHIC PLASTICITY OF THESE SPECIES. THREE TARGET ECHINOID SPECIES WITH ALREADY KNOWN A PRIORI CONTRASTED TROPHIC STRATEGIES WILL BE STUDIED: STERECHINUS DIADEMA, ABATUS CORDATUS, AND CTENOCIDARIS NUTRIX. ELEMENTAL (C/N) AND ISOTOPIC ANALYSES (¹³C, ¹⁵N) WILL ALSO BE PERFORMED ON DIFFERENT ORGANIC MATTER SOURCES (DISSOLVED ORGANIC MATTER OF SEA WATER, SEDIMENT ORGANIC MATTER, MACROALGAE) AND COMPARED WITH OTHER PRIMARY AND SECONDARY CONSUMERS (SPONGES, KEY MARINE INVERTEBRATES). THIS WILL BE COMPLETED BY DIGESTIVE TRACK CONTENT ANALYZES OF SAMPLED SPECIMENS.