Olesia N. Makhutova

Production of EPA and DHA in aquatic ecosystems and their transfer to the land

Most omnivorous animals, including humans, have to some degree relied on physiologically important polyunsaturated fatty acids (PUFAs), such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from food. Only some taxa of microalgae, rather than higher plants can synthesize de novo high amounts of EPA and DHA. Once synthesized by microalgae, PUFA are transferred through trophic chain to organisms of higher levels. Thus, aquatic ecosystems play the unique role in the Biosphere as the principal source of EPA and DHA for most omnivorous animals, including inhabitants of terrestrial ecosystems. PUFA are transferred from aquatic to terrestrial ecosystems through riparian predators, drift of carrion and seaweeds, emergence of amphibiotic insects, and water birds. The essential PUFA are transferred through trophic chains with about twice higher efficiency than bulk carbon. Thereby, PUFA are accumulated, rather than diluted in biomass of organisms of higher trophic levels, e.g., in fish. Mankind is faced with a severe deficiency of EPA and DHA in diet. Although additional sources of PUFA supply for humans, such as aquaculture, biotechnology of microorganisms and transgenic terrestrial oil-seed producing plants are developed, natural fish production of aquatic ecosystems will remain one of the main sources of EPA and DHA for humans. Aquatic ecosystems have to be protected from anthropogenic impacts, such as eutrophication, pollution and warming, which reduce PUFA production.

Efficiency of transfer of essential polyunsaturated fatty acids versus organic carbon from producers to consumers in a eutrophic reservoir

One of the central paradigms of ecology is that only about 10% of organic carbon production of one trophic level is incorporated into new biomass of organisms of the next trophic level. Many of energy-yielding compounds of carbon are designated as ‘essential’, because they cannot be synthesized de novo by consumers and must be obtained with food, while they play important structural and regulatory functions. The question arises: are the essential compounds transferred through trophic chains with the same efficiency as bulk carbon? To answer this question, we measured gross primary production of phytoplankton and secondary production of zooplankton and content of organic carbon and essential polyunsaturated fatty acids of ω-3 family with 18–22 carbon atoms (PUFA) in the biomass of phytoplankton and zooplankton in a small eutrophic reservoir during two summers. Transfer efficiency between the two trophic levels, phytoplankton (producers) and zooplankton (consumers), was calculated as ratio of the primary production versus the secondary (zooplankton) production for both carbon and PUFA. We found that the essential PUFA were transferred from the producers to the primary consumers with about twice higher efficiency than bulk carbon. In contrast, polyunsaturated fatty acids with 16 carbon atoms, which are synthesized exclusively by phytoplankton, but are not essential for animals, had significantly lower transfer efficiency than both bulk carbon, and essential PUFA. Thus, the trophic pyramid concept, which implicitly implies that all the energy-yielding compounds of carbon are transferred from one trophic level to the next with the same efficiency of about on average 10%, should be specified for different carbon compounds.

Is the Fatty Acid Composition of Freshwater Zoobenthic Invertebrates Controlled by Phylogenetic or Trophic Factors

We studied the fatty acid (FA) content and composition of ten zoobenthic species of several taxonomic groups from different freshwater bodies. Special attention was paid to essential polyunsaturated fatty acids, eicosapentaenoic acid (EPA, 20:5n-3), docosahexaenoic acid (DHA, 22:6n-3), and arachidonic acid (ARA, 20:4n-6); and the n-3/n-6 and DHA/ARA ratios, which are important for consumers of higher trophic levels, i.e., fish. The content and ratios of these FA varied significantly in the studied zoobenthic species, consequently, the invertebrates were of different nutritional quality for fish. Eulimnogammarus viridis (Crustacea) and Dendrocoelopsis sp. (Turbellaria) had the highest nutrition value for fish concerning the content of EPA and DHA and n-3/n-6 and DHA/ARA ratios. Using canonical correspondence analysis we compared the FA profiles of species of the studied taxa taking into account their feeding strategies and habitats. We gained evidence that feeding strategy is of importance to determine fatty acid profiles of zoobenthic species. However, the phylogenetic position of the zoobenthic species is also responsible and may result in a similar fatty acid composition even if species or populations inhabit different water bodies or have different feeding strategies.

A comparison of the fatty acid composition of Gammarus lacustris and its food sources from a freshwater reservoir, Bugach, and the saline Lake Shira in Siberia, Russia

We studied fatty acid (FA) composition in samples from bodies and intestinal contents of the littoral amphipod Gammarus lacustris Sars, from the Bugach freshwater reservoir. Simultaneously, samples of seston and bottom sediments were also collected from the reservoir during early August. There were no differences in FA composition of gut contents, seston and sediments of pebbly bottom. Seston was the main food source of Gammarus but some FAs Gammarus got from sediments. The FA composition of G. lacustris and seston from the Bugach freshwater reservoir were compared with those of the animals from the saltwater Lake Shira (Siberia). While FA composition of the two Gammarus populations differed significantly, those of seston were practically similar: the composition of long-chain unsaturated fatty acids, 20:5ω3, 22:6ω3 and 20:4ω6, were significantly higher in animals from saline Shira Lake, whereas 16:1 and 16:0 were higher in the freshwater populations of amphipods from the Bugach freshwater reservoir. Taking into account the relevant literature data, we hypothesise that this difference in C16 acid might be a distinguishing characteristic of FA composition of freshwater and saltwater crustaceans.

Study of non-consumptive mortality of Crustacean zooplankton in a Siberian reservoir using staining for live/dead sorting and sediment traps

We studied non-consumptive (non-predatory) mortality of Daphnia and Cyclops vicinus during four sampling seasons. Mortality estimations were based on live/dead sorting using special staining and measurements of sedimentation rates for dead individuals, depended on wind speed. Original equations were used for calculations. The estimated specific non-consumptive mortality never had biologically senseless negative values, which were often obtained on the basis of the other ways of mortality estimations, and was in a good agreement with other components of population dynamics. As found, the non-consumptive mortality was the important, often the determinant component of the zooplankton population dynamics.

Stable isotope composition of fatty acids in organisms of different trophic levels in the Yenisei River.

We studied four-link food chain, periphytic microalgae and water moss (producers), trichopteran larvae (consumers I), gammarids (omnivorous – consumers II) and Siberian grayling (consumers III) at a littoral site of the Yenisei River on the basis of three years monthly sampling. Analysis of bulk carbon stable isotopes and compound specific isotope analysis of fatty acids (FA) were done. As found, there was a gradual depletion in 13C contents of fatty acids, including essential FA upward the food chain. In all the trophic levels a parabolic dependence of δ13C values of fatty acids on their degree of unsaturation/chain length occurred, with 18:2n-6 and 18:3n-3 in its lowest point. The pattern in the δ13C differences between individual fatty acids was quite similar to that reported in literature for marine pelagic food webs. Hypotheses on isotope fractionation were suggested to explain the findings.

Feeding spectra of Arctodiaptomus salinus (Calanoida, Copepoda) using fatty acid trophic markers in seston food in two salt lakes in South Siberia (Khakasia, Russia)

During two vegetation seasons (2004–2005), we compared feeding spectra of Arctodiaptomus salinus (Calanoida, Copepoda) populations inhabiting two neighboring salt lakes, Shira and Shunet, Khakasia, Russia, using fatty acid (FA) trophic markers. Sestonic FA composition in two lakes moderately differed, whereas levels of diatom FA markers were higher in Lake Shunet and of Cyanobacteria and green algae markers in Lake Shira. In general, markers in storage lipids—triacylglycerols (TAG) of A. salinus—reflected the differences in sestonic composition of the two lakes. Nevertheless, TAG fraction was also enriched by FA trophic markers of the minor components of seston, which were selectively ingested by the animals. In Lake Shira, A. salinus had significantly higher concentrations of bacterial FA markers in TAG. In Lake Shunet, TAG of A. salinus contained significantly higher relative amounts of 18:4ω3, 18:5ω3 and C22 polyunsaturated fatty acids (PUFA), which indicated marked contribution of cryptophytes or (and) flagellates into the diet. Laboratory experiments showed feeding on Cryptomonas and sulfur purple bacteria in Lake Shunet and ciliates and colonial picoplankton in both lakes, and generally confirmed the differences in FA trophic markers in A. salinus between the lakes. The two populations of A. salinus markedly differed in levels of essential long-chain PUFA, eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids, although the levels of these FA in seston were quite similar between the two lakes. The higher levels of the essential ω3 PUFA in A. salinus in Lake Shunet may be an adaptive response of the animals to a vertical stratification of physico-chemical conditions and significantly higher salinity levels at the boundary of adjacent bottom layer in this lake.

Content of essential polyunsaturated fatty acids in three canned fish species

Three canned fish species—Pacific saury (Cololabis saira), Pacific herring (Clupea harengus) and Baltic sprat (Sprattus sprattus)—most common and popular in Russia, were analyzed for fatty acids. Special attention was paid to long-chain essential polyunsaturated fatty acids: eicosapentaenoic acid (20:5ω3) and docosahexaenoic acid (22:6ω3). Sums of eicosapentaenoic acid and docosahexaenoic acid in saury, herring and sprat were, on average, 2.42, 1.80 and 1.43 g/100 g product, respectively. Contents of these essential acids in all the canned fish species were found to be very high compared with many other fish reported in the available literature. All the canned fish appeared to be highly valuable products for human nutrition concerning the content of eicosapentaenoic and docosahexaenoic acids.

Feeding spectra of bivalve mollusks Unio and Dreissena from Kanevskoe Reservoir, Ukraine: are they food competitors or not?

BackgroundOne of the most abundant freshwater invaders is Dreissena polymorpha which provide wide-ranging direct and indirect impacts on the invaded ecosystems. A particularly notable impact on benthic communities is the extinction of native mollusks of the order Unionida. However, the settlement of D. polymorpha on unionids shells in Kanevskoe Reservoir did not increase native unionid mortality. Since the reason for the successful coexistence of native unionids and invading dreissenids in Kanevskoe Reservoir is unknown, we hypothesized that these mollusks have different feeding spectra. To evaluate this hypothesis, we compared feeding spectra of the mollusks using a fatty acid (FA) marker analysis.ResultsSignificant differences in the number and percentages of FAs were found among the mollusks and their food sources, seston, and sediments. Analyses of FA trophic markers in mollusk tissues showed that U. tumidus and Dreissena species mainly consumed algae (greens, diatoms, and dinoflagellates), cyanobacteria, and detritus particles enriched with bacteria. According to the multivariate statistical analysis, the mollusks had different feeding spectra: Dreissena species fed on planktonic sources, while U. tumidus mostly consumed food sources of benthic origin, mainly detritus. In addition, U. tumidus and Dreissena species differed in percentages of long-chain polyunsaturated FAs of n-3 and n-6 families and specific FAs which they could synthesize (20:1n-13 and 22:3 ∆7,13,16).ConclusionsU. tumidus and Dreissena species obviously obtained foods of different qualities. Dreissena consumed plankton species, i.e., more-valuable food, while U. tumidus fed on detritus and phytobenthic species which were of a lower food quality in terms of levels of physiologically important eicosapentaenoic and docosahexaenoic fatty acids. We concluded that the different feeding spectra of mollusks and adaptations of U. tumidus, the synthesis of specific FAs, might be the basis for the successful coexistence of native species and invaders for a long time.

Comparison of nutrition range in Dreissena polymorpha and Dreissena bugensis mussels by biochemical markers

Based on biochemical markers, we studied the nutrition ranges of populations of Dreissena polymorpha and Dreissena bugensis mussels that inhabit the Volga reach of the Rybinsk reservoir and differ in the long-term population dynamics. Features of the nutrition ranges of mussels are regarded as the probable cause of changes in the number of mollusca.