Inferring the feeding habit of the deep-sea ‘big mouth’ ascidian tunicate, Megalodicopia hians, by fatty acid analysis

Colonies of the ‘big mouth’ tunicate, Megalodicopia hians, were first discovered in Toyama Bay, Japan Sea. The suspension-feeding habit of this organism is inferred from the diets in the oral aperture and feces. The colonies were mainly found on the steep slope (water depth > 1 km), particularly at the sites characterized by exposed rocks and/or thin sediment. Most of the individuals faced ‘mouth’ downward, suggesting that they trap suspended matters adrift or re-suspended sediment in the upward current. We have analyzed the composition of total fatty acids of Megalodicopia hians in comparison with those of other bathyal benthic animals having various feeding habits and phylogenies. A dendrogram was constructed by the cluster analysis of the fatty acid compositions. Primary grouping in the fatty acid-based dendrogram reflected the feeding habits rather than the phylogenic relationships of the studied benthic animals. An inference from the dendrogram suggested that suspension-feeding is usual but occasionally this organism engages in the scavenging habit, in general agreement with the inference from the diet analysis.