Fatty-Acid and Stable-Isotope Compositions in Shallow-Water Bivalve Mollusks and their Food

Abstract

We conducted a comparative analysis of the fatty acid (FA) composition and the ratios of stable isotopes of carbon (δ13C) and nitrogen (δ15N) in soft tissues of ten species of bivalve mollusks collected simultaneously on adjacent biotopes in shallow Vostok Bay (the Sea of Japan). Comparison of the FA composition of the lipids of digestive gland and all soft tissues showed that the percentages of C16 and C18 marker FAs were greater in the digestive gland and the levels of marker C20 and C22 FAs were, in most cases, higher in soft tissues. According to the results of cluster analysis and principal component analysis, four groups of samples were identified with a similarity of the FA composition of more than 80% within groups. The carbon stableisotope ratios varied within very wide limits in the studied species of bivalves; the range of δ13C variations was 8.1‰. The range of δ15N variations was much smaller, 2.5‰. Two pairs of species of mollusks (Saxidomus purpurata–Protothaca euglypta and P. jedoensis–Diplodonta semiasperoides) did not differ in the values of both δ15N and δ13C, the remaining species differed in at least one of these parameters. The greatest similarity of the FA composition and stable-isotope ratios was found in species that inhabit similar substrates, except Macoma irus and D. semiasperoides. Particularly marked differences in the FA composition and stable-isotope ratios were found between a filter-/surface deposit-feeder M. irus and filter-feeders Arca boucardi and Mytilus coruscus that live next to this species.