High level of tetracosapolyenoic fatty acids in the cold-water mollusk Tochuina tetraquetra is a result of the nudibranch feeding on soft corals

Abstract

Fatty acid (FA) markers are used to trace predator–prey relationships in the marine environment. Soft corals contain tetracosapolyenoic acids (TPA), namely 24:5n-6 and 24:6n-3, which are considered as octocoral FA markers. The nudibranch mollusks are known to feed on soft corals. To check whether TPA are transferred from soft corals to nudibranch mollusks during their nutrition, we determined and compared FA compositions of total lipids of Tochuina tetraquetra and soft corals (Acanella sp., Anthomastus rylovi, Gersemia fruticosa, and Paragorgia arborea) collected together near the Kuril Islands (the depths of 80–550 m). FA compositions of T. tetraquetra, Acanella sp. and A. rylovi were described for the first time. In Acanella sp., G. fruticosa, A. rylovi, and P. arborea, the average contents of TPA were 6.5, 13.4, 5.9, and 12.0 % of total FAs, whereas the 24:5n-6/24:6n-3 ratio was 1.0, 1.4, 5.4, and 2.6, respectively. The high level of TPA (21.7 %) found in T. tetraquetra indicates that 24:5n-6 and 24:6n-3 are transferred from soft corals to the mollusks during their feeding and accumulated in mollusk tissues. The most possible feed source of the mollusk is suggested to be G. fruticosa and/or Acanella sp., because the 24:5n-6/24:6n-3 ratios in T. tetraquetra and these soft corals were similar. Thus, the TPA could be used as FA markers to estimate a proportion of soft corals in feeding of cold-water nudibranch mollusks.