Vladimir I. Kharlamenko

The composition of fatty acids and stable isotopes in the detritophage Acila insignis (Gould, 1861) (Bivalvia: Nuculidae): Searching for markers of a microbial food web

The fatty acid composition and stable isotope ratios of carbon, nitrogen, and sulfur were analyzed in the protobranch bivalve Acila insignis, a selective detritophage inhabiting subtidal sand sediments of Vostok Bay (Sea of Japan). Soft tissues of A. insignis contained abnormally high concentrations of the polyunsaturated arachidonic acid, 20: 4(n-6), and a rare monounsaturated fatty acid 20: 1(n-13), which distinguishes this species from other bivalves. The high concentrations of these fatty acids in A. insignis, together with the low values of σ34S and the high values of σ13C and σ15N, are probably a result of feeding on the microbial food web.

The fatty-acid composition and nutrition of deep-sea holothurians from the Sea of Okhotsk

The results of a comparative study of the fatty-acid composition in eight species of holothurians that were collected in the Sea of Okhotsk in the area of the Kuril Islands (depths of 90–560 m) are presented. It is shown that interspecific differences in the fatty-acid compositions of the holothurians were consistent with the isotope composition (δ13C and δ15N) and the structural features of the tentacles and the lifestyle of holothurians, as indicators of trophic resources used by these holothurians. According to the results of the cluster analysis, the holothurians were divided into three groups. The first group included suspension-feeding dendrochirotides Eupentacta pusilla and Pseudocnus fallax with a high content of the fatty acid 20:5(n-3), which is a marker of diatoms, and with the δ15N values that are typical of consumers of suspended organic matter. The second group consisted of the dendrochirotides Psolus chitonoides and Psolidium sp. with a much lower content of 20:5 (n-3) and higher contents of 20:4 (n-6) and 22:6 (n-3), as well as high values of δ15N, which are typical of surface deposit-feeders. The third group consisted of surface and subsurface depositfeeders, Chiridota sp., Molpadia orientalis, Pseudostichopus mollis, and Synallactes nozawai. Very high contents of 20: 4 (n-6) and 21: 4 (n-7) were typical of the third group and the highest values of δ15N, indicating feeding on repeatedly recycled organic matter.

The bitter crab syndrome in commercial crabs in the Western part of the Bering and Chukchi Seas

We studied the distribution of the “bitter-crab” syndrome, a disease caused by the parasitic dinoflagellate Hematodinium sp., in eight commercial species of crabs in the west of the Bering and Chukchi seas. The crabs (25 388 individuals) were sampled during bottom trawl surveys of July‒September 2010 and October‒November 2012. The disease was first identified visually by a color change of the exoskeleton and the hemolymph of the animals and then using microscope analysis of hemolymph samples. Infestation was detected in crabs of three species, Chionoecetes opilio, C. bairdi, and Paralithodes platypus. The prevalence of the disease (the percent of infected individuals relative to all of those examined) in C. bairdi and P. platypus was very low, 0.1 and 0.3%, respectively. Infestation was widespread among C. opilio, its peak in the Bering Sea was in the fall. The average prevalence of the crab disease in different areas of the Bering Sea ranged from 0.8 to 10.8%. A high rate of crab infection was recorded in the Korfa Bay. In the Chukchi Sea, the average prevalence was 2%. Infestation by Hematodinium sp. was not revealed in the deep-sea snow crabs Chionoecetes tanneri and C. angulatus, and in three species of lithodid crabs, Paralithodes camtschaticus, P. brevipes, and Lithodes couesi. This can be explained by the small sample volume and/or ecology of these species, since the disease was registered in other areas in four of them.

Polyunsaturated molecular species of galactolipids: Markers of zooxanthellae in a symbiotic association of the soft coral Capnella sp. (Anthozoa: Alcyonacea)

A method that uses marker fatty acids (FAs) is widely applied in investigations of trophic and symbiotic relationships. In a search for new lipid markers, we determined the total lipid FA composition, as well as the composition of molecular species of mono- and digalactosyl diacylglycerols (MGDGs and DGDGs), which are specific galactolipids of thylakoid membranes, in zooxanthellae (endosymbiotic dinoflagellates) of the tropical soft coral Capnella sp. Some FAs of zooxanthellae were suggested for use as marker polyunsaturated FAs (PUFAs). Thirteen molecular species of MGDGs and ten molecular species of DGDGs were detected using the method of high-resolution tandem mass spectrometry. All marker PUFAs of zooxanthellae were found in acyl groups of galactolipids. The major molecular species of DGDGs (18:4/18:4, 18:4/20:5, and 16:2/22:6) and the unique molecular species of MGDGs (16:4/18:5) were described. The identification of several polyunsaturated molecular species of galactolipids that contain marker FAs allowed us to propose that this lipid group be used as molecular lipid markers of zooxanthellae for the study of symbiont–host interactions in soft corals.

Occurrence of Hexacosapolyenoic Acids 26:7(n-3), 26:6(n-3), 26:6(n-6) and 26:5(n-3) in Deep-Sea Brittle Stars from Near the Kuril Islands

Significant amounts of polyunsaturated fatty acids (PUFA) with a chain length of 26 carbon atoms were detected in lipids of five deep water species of Ophiuroidea besides common fatty acids with chain lengths between 14 and 24. By means of hydrogenation, GC–MS of the methyl esters, and 4,4-dimethyloxazoline (DMOX) derivatives of these C26 acids were characterized as 5,8,11,14,17,20,23-hexacosaheptaenoic [26:7(n-3)]; 8,11,14,17,20,23-hexacosahexaenoic [26:6(n-3)]; 5,8,11,14,17,20- hexacosahexaenoic [26:6(n-6)]; and 11,14,17,20,23-hexacosapentaenoic [26:5(n-3)]. Concentrations of these acids varied from 0.3 to 4.5 mol% of the total FA. In all the samples investigated, the main component of C26PUFA was hexacosaheptaenoic acid 26:7(n-3). These C26PUFA are localized mainly in polar lipids. The presence of the possible biosynthesis precursors suggests that the C26PUFA are produced by the brittle stars, and are not accumulated from food sources. This finding can also explain the presence of small amounts of the 26:7(n-3) acid detected earlier in flesh lipids of the roughscale sole Clidoderma asperrimum, which feeds on deep water brittle stars. We suggest a possible scheme of the biosynthesis of C26 PUFA.

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

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.