In situ diet patterns and health status of cold-water corals in the Lacaze-Duthiers canyon (NW Mediterranean Sea): insights from fatty acid biomarkers on lipid classes

Hydrodynamic and food supply favourable conditions in the Lacaze-Duthiers Canyon (northwestern Mediterranean Sea) have supported the establishment of deep-sea corals, with some of the highest densities recorded in the Mediterranean. However, increasing pressures on these vulnerable habitats raise critical questions about their ecological status and resilience to environmental changes, emphasising the need to understand their trophic ecology. This study provides the most detailed analysis to date of the lipid profiles and fatty acid signatures of two key framework-building cold-water corals, Madrepora oculata and Desmophyllum pertusum (syn. Lophelia pertusa ), offering insights into their feeding strategies, dietary requirements, and nutritional condition. The results reveal that lipid classes exhibit distinct fatty acid compositions based on functional roles (storage vs. structural). Fatty acid trophic markers (FATM) indicative of herbivorous calanoids, carnivorous copepods, and phytodetritus were detected in the storage lipids (waxes and triglycerides) of both species, yet no FATM was specific to either species. This indicates a mixed diet and dietary overlap between the two corals. However, the composition of storage lipids varied significantly across samples, likely reflecting (1) species-specific feeding preferences, with D. pertusum showing greater reliance on overwintering copepods, and (2) the dynamic availability of food resources within the canyon. Phospholipids were enriched in polyunsaturated fatty acids (PUFA), suggesting that dietary inputs are of sufficiently high quality to meet the metabolic demands of cold-water corals. High levels of storage lipids, primarily long-term reserves (wax esters) enriched in PUFA and zooplankton markers, underscore the good nutritional status of cold-water corals in the Lacaze-Duthiers Canyon. • Distinct fatty acid profiles identified in phospholipids and storage lipids. • High PUFA content in phospholipids shows selective assimilation of dietary fatty acids. • Trophic markers show overall dietary overlap and strong reliance on mesozooplankton. • Feeding preferences and food source dynamic account for local and temporal variability. • High storage lipids reveal favourable nutritional condition in cold-water corals.