Fatty acid composition as an indicator of the trophic position of abyssal megabenthic deposit feeders in the Kuril Basin of the Sea of Okhotsk

Abstract

This study examines the fatty acid (FA) composition in eight species of deposit feeders, including holothurians, echiurans, sipunculan, polychaete and bivalve mollusc from the Kuril Basin of the Sea of Okhotsk. Most of the FAs in the species studied have been described previously for abyssal deposit feeders, but 20:2(n-12), 22:4(n-8), and 22:5(n-5) were new among megabenthic invertebrates. Principal component analysis indicated sample separation of the deposit feeders into three groups. The first group included subsurface deposit feeders, and the other two consisted of surface deposit feeders. All groups differed in the ratio of 20:5(n-3) to 20:4(n-6). This ratio was 0.2–0.4 in the subsurface deposit feeder Molpadia musculus Risso, 1826 (group I) and 0.6–0.9 in the surface deposit feeding echiuran Pseudoikedella achaeta (Zenkevitch, 1958) and the elasipodid holothurian Psychropotes raripes Ludwig, 1893 (group II). In the second group of surface deposit feeders (group III), this ratio was a little larger in the polychaete Travisia sp. (1.3) and was much larger (2.1–2.5) in the echiuran Alomasoma nordpacificum Zenkevitch, 1958, the sipunculan Golfingia margaritacea (Sars, 1851), and the holothurian Peniagone dubia (D′yakonov and Savel'eva in D′yakonov et al., 1958). Unlike previous data, we found that the most abundant megabenthos species in the basin are subsurface deposit feeders and two groups of surface deposit feeders.