Delayed feeding onset in cold-water coral larvae: first evidence of microalgal ingestion in Desmophyllum pertusum revealed by fluorescence microscopy

Abstract Successful larval recruitment in the cold-water coral Desmophyllum pertusum (formerly known as Lophelia pertusa ) is critical for population persistence and restoration efforts, yet little is known about their early life stages, in particular larval feeding and energy acquisition. Previous studies suggest that the formation of the oral pore (~ 14 days post-fertilization, dpf) and protractible mouth (~ 20 dpf) might indicate feeding readiness, but direct evidence of feeding onset has been lacking. In this study, we used fluorescence microscopy to investigate active feeding onset in D. pertusum larvae by tracking the development of the gastrovascular cavity (GVC) and the ingestion of microalgae. Despite early formation of oral structures, no food ingestion was observed at 22-25 dpf. Instead, feeding and internalization of food particles in the GVC were first detected at 38 dpf, coinciding with complete GVC differentiation, indicating a delayed onset of feeding compared to previous assumptions. These findings suggest that the presence of a mouth alone is insufficient for feeding and that complete digestive development is required. Our study provides: (1) the first direct evidence of microalgal ingestion in D. pertusum larvae, (2) a functional timeline linking morphological development to feeding capability, and (3) methodological validation of fluorescence microscopy for larval trophic studies. These findings redefine energy allocation timelines for this keystone species and establish critical baselines for conservation-focused larval rearing efforts.