Abyssal foraminifera as the main source of rare and new polyunsaturated fatty acids in deep-sea ecosystems

Many rare and new polyunsaturated fatty acids (FM) have been found in lipids of the foraminifera Reophax nodulosus, Crithionina sp. and Pyrgo sp. from the abyssal zone of the Kuril Basin (Sea of Okhotsk) and the adjacent abyssal area of Pacific Ocean, including the slope of Kuril-Kamchatka Trench. Polyunsaturated fatty acids (PUFAs) of the (n-5) family, previously unknown for marine organisms, dominated among PUFAs of the agglutinated foraminifera Reophax nodulosus. Moreover, 22:5(n-5) is the main FA of these foraminifera: its content (16.1-20.6%) is much higher than that of other PUFAs. The new FM 23:5(n-6), 23:4(n-9), 24:4(n-10), and 24:5(n-7) have been found in the agglutinated foraminifera Crithionina sp., with their concentrations reaching 1.4%, 0.5%, 0.1%, and 1.6%, respectively. Lipids of the calcareous foraminifera Pyrgo sp. contained new 23:4(n-7), 24:4(n-8), 24:5(n-9), 24:6(n-6), and 26:5(n-3) PUFAs at concentrations of 0.4%, 0.4%, 1.7%, 0.9%, and 0.9%, respectively. The possible pathways of biosynthesis of these rare and new FAs in foraminifera are proposed. These PUFAs are not found in the bottom sediments inhabited by these foraminifera, but have been detected in lipids of various abyssal deposit-feeding invertebrates (echiurans, irregular echinoids and sea stars). The presence of new FAs, previously known only from foraminifera, in such benthic animals is a valuable supplement to the study of trophic relationships of these animals.