FATTY ACID CONTENT AND CHEMICAL COMPOSITION OF FRESHWATER MICROALGAE1

Fatty acid (FA), total lipid, protein, amino acid, carbon, nitrogen, and phosphorus content was analyzed in 24 samples of freshwater microalgae. The samples originated from batch, continuous, or mass cultures in various growth phases and from net samples from lakewater. FA were analyzed quantitatively by using an internal standard in a GLC system and expressed as mg·g^?1 dry weight (DW). The FA of one group of blue-greens (e.g. Oscillatoria and Microcystis) were similar to those of the greens with higher amounts of 18C acids of the ω3 type compared to the ω6 type, whereas the other group (e.g. Anabaena and Spirulina) contained mostly ω6 acids. The flagellates, a taxonomically diverse group, were characterized by high amounts of long-chained (20–22 C) polyunsaturated FA (PUFA), particularly of the ω3 type. The ω3/ω6 ratio appears to be highest in algae in the exponential growth phase. The increased lipid content in stressed algae was mostly due to increased saturated fatty acids and ω6 acids, whereas the valuable ω3 acids were unchanged or even decreased. Amino acid composition (% of total amino acids) did not vary much betaken species, but when analyzed quantitatively (mg-g^?1 DW), varied considerably between species and within species in different growth phases. The nitrogen and phosphorus contents were variable in all three algal groups. The relationship between PUFA and phosphorus content differed among the algal groups. The data suggest that PUFA in the phospholipids consist mostly ω3 acids.     

Fatty acid composition of consumers in boreal lakes – variation across species,space and time

1. Fatty acids (FAs) have been widely applied as trophic biomarkers in aquatic food web studies. However, current knowledge of inter‐ and intraspecific variation in consumer FA compositions across spatial and temporal scales is constrained to a few pelagic taxa. 2. We analysed the FAs of 22 taxa of benthic macroinvertebrates, zooplankton and fish collected from the littoral, pelagic and profundal habitats of nine boreal oligotrophic lakes over spring, summer and autumn. We quantified and compared the FA variance partitions contributed by species identity (i.e. an integrative effect of phylogenetic origin, life history and functional feeding guild of individual taxa), site and season using partial redundancy analysis both on all consumers and on benthic arthropods alone. 3. Species identity alone contributed 84.4 and 72.8% of explained FA variation of all consumers and benthic arthropods, respectively. Influences of site, season and all joint effects accounted for 0–11.3% only. Fatty acid profiles of primary consumers differentiated below class level, but those of predators were distinguishable only when they became more taxonomically distinct (i.e. among classes or higher). 4. Pelagic and profundal consumers showed stronger reliance on autochthonous resources than did their littoral counterparts as reflected by their higher ω3 to ω6 FA ratios. Polyunsaturated FAs (PUFAs) were increasingly retained with trophic levels, and saturated FAs (e.g. FA 16 : 0) gradually reduced. Ecologically, this trade‐off enhances the trophic transfer efficiency and confirms the importance of PUFA‐rich autotrophs in aquatic food webs. 5. Our findings indicate strong interspecific differences in FA requirements and assimilation among aquatic consumers from a wide range of taxonomic levels, habitats and lakes. Consumers were able to maintain homoeostasis in FA compositions across spatial and temporal changes in resource FAs, but consumer homoeostasis did not limit the effectiveness of FAs as trophic biomarkers.     

Food sources and lipid retention of zooplankton in subarctic ponds

1. Subarctic ponds are seasonal aquatic habitats subject to short summers but often have surprisingly numerous planktonic consumers relative to phytoplankton productivity. Because subarctic ponds have low pelagic productivity but a high biomass of benthic algae, we hypothesised that benthic mats provide a complementary and important food source for the zooplankton. To test this, we used a combination of fatty acid and stable isotope analyses to evaluate the nutritional content of benthic and pelagic food and their contributions to the diets of crustacean zooplankton in 10 Finnish subarctic ponds. 2. Benthic mats and seston differed significantly in total lipids, with seston (62.5 μg mg^?1) having approximately eight times higher total lipid concentrations than benthic mats (7.0 μg mg^?1). Moreover, the two potential food sources differed in their lipid quality, with benthic organic matter completely lacking some nutritionally important polyunsaturated fatty acids (PUFA), most notably docosahexaenoic acid and arachidonic acid. 3. Zooplankton had higher PUFA concentrations (27–67 μg mg^?1) than either of the food sources (mean benthic mats: 1.2 μg mg^?1; mean seston: 9.9 μg mg^?1), indicating that zooplankton metabolically regulate their accumulation of PUFA. In addition, when each pond was evaluated independently, the zooplankton was consistently more ¹³C‐depleted (δ¹³C ?20 to ?33‰) than seston (?23 to ?29‰) or benthic (?15 to ?27‰) food sources. In three ponds, a subset of the zooplankton (Eudiaptomus graciloides, Bosmina sp., Daphnia sp. and Branchinecta paludosa) showed evidence of feeding on both benthic and planktonic resources, whereas in most (seven out of 10) ponds the zooplankton appeared to feed primarily on plankton. 4. Our results indicate that pelagic primary production was consistently the principal food resource of most metazoans. While benthic mats were highly productive, they did not appear to be a major food source for zooplankton. The pond zooplankton, faced by strong seasonal food limitation, acquires particular dietary elements selectively.     

Nutrient dynamics and ecosystem metabolism in the Bay of Blanes (NW Mediterranean)

The dynamics of the nutrient pools and their stoichiometry as well as their control by ecosystem metabolism (benthic and planktonic) and benthic–pelagic exchanges (sedimentation rates and sediment waterfluxes) were examined in the Mediterranean littoral (Blanes Bay, NE Spain). Dissolved organic nitrogen comprised about half of the nitrogen present in the water column and the carbon pool was dominated by the inorganic pool (95% of the carbon present in the water column). The dissolved and particulate organic pools were deficient in P relative to C and N, indicating a rapid recycling of P from organic matter. The pelagic compartment was heterotrophic, supported by significant allochthonous inputs of land material, which also contributed greatly to the sedimentary inputs (37% of total sedimenting carbon). In contrast, the benthic compartment was autotrophic, with the excess net benthic community production balancing the deficit in pelagic community production, leading to metabolic equilibrium at the station studied. Sedimentary inputs of nitrogen, phosphorus and silicon exceeded the benthic release, indicating that the benthic compartment acted as a sink for nutrients, consistent with its autotrophic nature. Carbon inputs to the benthic compartment also exceeded requirements, due to the allochthonous subsidies to the system, so that the benthic compartment stored or exported organic carbon. An erratum to this article can be found at .     

Light and nutrients regulate energy transfer through benthic and pelagic food chains

The amount of energy flowing to top trophic levels depends on primary production and the efficiency at which it is converted to production at each trophic level. In aquatic systems, algal production is often limited by light and nutrients, and the nutritional quality of algae depends on the relative balance of these two resources. In this study, we used a mesocosm experiment to examine how light and nutrient variation affected food chain efficiency (FCE, defined as the proportion of primary production converted to top trophic level production), using a food web with benthic and pelagic food chains. We also related variation in benthic and pelagic efficiencies to the nutritional quality of primary producers, i.e. carbon:nitrogen:phosphorus stoichiometry. As predicted, pelagic and benthic FCEs were highest under low light/high nutrient conditions, the treatment with the best algal food quality, i.e. the lowest C:nutrient ratios. Pelagic FCE and pelagic herbivore efficiency (HE_P) were more responsive than benthic FCE to variation in light and nutrients. Furthermore, pelagic FCE and HE_P were highly correlated with algal C:P, suggesting ‘carryover effects’ of algal food quality on carnivores (larval fish) via effects on herbivore (zooplankton) quality. Benthic (tadpole) production was primarily explained by primary production rate, suggesting food quantity rather than quality drives their production. However, benthic FCE was also highest at low light/high nutrients and was significantly correlated with food quality. The stronger effect of food quality in mediating pelagic compared to benthic efficiencies, is consistent with differences in the stoichiometric mismatches between algae and consumers. Pelagic FCE and HE_P were more likely to be P‐limited, whereas benthic FCE was more likely N‐limited. This study is the first to examine both pelagic and benthic FCE within the same system, and highlights the importance of differential consumer needs in determining how food quality affects energy transfer efficiency.     

Resource partitioning between Pacific walruses and bearded seals in the Alaska Arctic and sub-Arctic

Climate-mediated changes in the phenology of Arctic sea ice and primary production may alter benthic food webs that sustain populations of Pacific walruses (Odobenus rosmarus divergens) and bearded seals (Erignathus barbatus). Interspecific resource competition could place an additional strain on ice-associated marine mammals already facing loss of sea ice habitat. Using fatty acid (FA) profiles, FA trophic markers, and FA stable carbon isotope analyses, we found that walruses and bearded seals partitioned food resources in 2009–2011. Interspecific differences in FA profiles were largely driven by variation in non-methylene FAs, which are markers of benthic invertebrate prey taxa, indicating varying consumption of specific benthic prey. We used Bayesian multi-source FA stable isotope mixing models to estimate the proportional contributions of particulate organic matter (POM) from sympagic (ice algal), pelagic, and benthic sources to these apex predators. Proportional contributions of FAs to walruses and bearded seals from benthic POM sources were high [44 (17–67)% and 62 (38–83)%, respectively] relative to other sources of POM. Walruses also obtained considerable contributions of FAs from pelagic POM sources [51 (32–73)%]. Comparison of δ¹³C values of algal FAs from walruses and bearded seals to those from benthic prey from different feeding groups from the Chukchi and Bering seas revealed that different trophic pathways sustained walruses and bearded seals. Our findings suggest that (1) resource partitioning may mitigate interspecific competition, and (2) climate change impacts on Arctic food webs may elicit species-specific responses in these high trophic level consumers.     

Sedimentation of Nodularia spumigena and distribution of nodularin in the food web during transport of a cyanobacterial bloom from the Baltic Sea to the Kattegat

Nodularia spumigena is a toxic cyanobacteria that blooms in the Baltic Sea every year. In the brackish water of the Baltic Sea, its toxin, nodularin, mainly affects the biota in the surface water due to the natural buoyancy of this species. However, the fate of the toxin is unknown, once the cyanobacteria bloom enters the more saline waters of the Kattegat. In order to investigate this knowledge gap, a bloom of N. spumigena was followed during its passage, carried by surface currents, from the Baltic Sea into the Kattegat area, through the Öresund strait. N. spumigena cells showed an increased cell concentration through the water column during the passage of the bloom (up to 130 10³ cells ml⁻¹), and cells (4.2 10³ cells ml⁻¹) could be found down to 20 m depth, below a pycnocline. Sedimentation trap samples from below the pycnocline (10–12 m depth) also showed an increased sedimentation of N. spumigena filaments during the passage of the bloom. The toxin nodularin was detected both in water samples (0.3–6.0 μg l⁻¹), samples of sedimenting material (a toxin accumulation rate of 20 μg m^-2 day⁻¹), zooplankton (up to 0.1 ng ind.⁻¹ in copepods), blue mussels (70–230 μg kg⁻¹ DW), pelagic and benthic fish (herring (1.0–3.4 μg kg⁻¹ DW in herring muscle or liver) and flounder (1.3-6.2 μg kg⁻¹ DW in muscle, and 11.7-26.3 μg kg⁻¹ DW in liver). A laboratory experiment showed that N. spumigena filaments developed a decreased buoyancy at increased salinities and that they were even sinking with a rate of up to 1,7 m day⁻¹ at the highest salinity (32 PSU). This has implications for the fate of brackish water cyanobacterial blooms, when these reach more saline waters. It can be speculated that a significant part of the blooms content of nodularin will reach benthic organisms in this situation, compared to blooms decaying in brackish water, where most of the bloom is considered to be decomposed in the surface waters.     

Fatty acid content of the dorsal muscle—an indicator of fat quality in freshwater fish

In 56 samples of freshwater fish, most were low in fat, ≤ 5% of dry weight (D.W.), and the sum of all fatty acids (ΣFA) was about 2% of D.W. Trout, whitefish, and grayling had the highest content of the long-chained FA. of ω3 type, EPA and DHA (1·7–2·6% of D.W.). Two large, low-fat pikes with ΣFA of about12–3% of D.W. and a medium-fat whitefish had the highest ω3/ω6 ratios, 8–9, whereas the fattiest fishes, eels from two lakes and the Baltic (ΣFA =17–26% of D.W.) had lower ω3/ω6 ratios, 1·1–1·8 (ω3 and ω6 FA are two important series of FA). The results indicate that ΣA controls the content of saturated FA (SAFA) and monounsaturated FA (MUFA), whereas the polyunsaturated FA (PUFA) was independent of ΣFA after a break point of about 10%ΣFA of D.W. The P/S ratio (PUFA/SAFA) and the PUFA/ΣFA ratio decreased with increased ΣFA, whereas the ω3/ω6 ratio showed no clear correlation to ΣFA. The difference in fatty acid patterns lay between low-fat and high-fat fishes, rather than between marine and freshwater fishes. The variation, both within and between species of the separate FA is small in fish with similar ΣFA content. Also, low-fat and medium-fat fishes tend to be more dietarily favourable than high-fat fishes, when considering the latest criteria for high nutritional value to humans. Abbreviations used in the text: FA, fatty acids; ΣFA, sum of all FA; AA, arachidonic acid (20 : 4ω6); EPA, eicosapentaenoic acid (20 : 5ω3); DHA, docosahexaenoic acid (22 : 6ω3); SAFA, saturated fatty acids; MUFA, monounsaturated fatty acids; PUFA, polyunsaturated fatty acids; D.W., dry weight; F.W. fresh weight; CV, coefficient of variation; ω3 FA, series of PUFA with the first double bond located at carbon number 3; ω6 FA, series of PUFA with the first double bond located at carbon number 6. The fatty acids are described by three numbers, x:ywz, where x=number of carbon atoms, y=number of double bonds, and z=position of the first double bond counted from the methyl end of the molecule.     

UV radiation and phosphorus interact to influence the biochemical composition of phytoplankton

1. Numerous laboratory studies have shown that food quality is suboptimal for zooplankton growth. However, little is known about how food quality is affected by the interaction of potential global change factors in natural conditions. Using field enclosures in a high altitude Spanish lake, seston was exposed to increasing phosphorus (P) concentrations in the absence and presence of UV radiation (UVR) to test the hypothesis that interactions between these factors affected the biochemical and stoichiometric composition of seston in ways not easily predicted from studies of single factors. 2. Phosphorus enrichment increased the content of total fatty acids (TFA), ω3‐polyunsaturated fatty acids (ω3‐PUFA) and chlorophyll‐a : carbon (Chl‐a : C) and C : N ratios in seston. The pronounced increase in ω3‐PUFA was largely explained by the enhancement of 18:3n‐3 (α‐linolenic acid). In contrast, P‐enrichment lowered the content of highly unsaturated fatty acids (HUFA), the HUFA : PUFA ratio and, at high P loads, seston C : P ratio. Although phytoplankton assemblages dominated by Chlorophytes were not rich in HUFA, seston in the control had substantially higher 20:4n‐6 (arachidonic acid, ARA) content (79% of HUFA) than did P‐enriched enclosures. 3. The UVR increased the content of ω3‐PUFA and TFA in seston at the two ends of the trophic gradient generated at ambient and high concentrations of P, but decreased seston C : P and HUFA at all points on this gradient. ARA was not detected in the presence of UVR. 4. The interaction between P and UVR was significant for seston HUFA and C : P ratios, indicating that the effect of UVR in reducing HUFA (decreased food quality) and C : P ratios (enhanced food quality) was most pronounced at the low nutrient concentrations characteristic of oligotrophic conditions and disappeared as P increased. Therefore, any future increase in UVR fluxes will probably affect most strongly the food quality of algae inhabiting oligotrophic pristine waters although, at least in the Mediterranean region, these effects could be offset by greater deposition of P from the atmosphere.     

Phospholipid characteristics and neutral lipid fatty acid composition related to temperature and nutritional conditions in ecologically important amphipod species from the northern Baltic Sea

Lipid composition of the benthic, stenothermal amphipod Monoporeia affinis collected from constantly cold deep-water (> 80 m) regions of the northern Baltic Sea was analysed in detail to study phospholipid characteristics, its relation to thermal adaptation as well as potential effects of food quality and seasonal variability. Similar measurements were performed on the littoral, eurythermic amphipod Gammarus spp. Fatty acid (FA) composition of storage lipids of Pontoporeia femorata, a sibling species of M. affinis, was also studied. Interannual and interspecies variability in selected FA was observed both in triacylglycerols (TAG) and phospholipids (PL). Differences in monounsaturated vs. polyunsaturated (MUFA/PUFA) FA combinations of phosphatidyl ethanolamine (PE) diacyl and alkylacyl subgroups were also observed. Seasonal variability in M. affinis was considerably lesser compared to Gammarus spp. A literature synopsis shows that in diacyl PE the share of the FA combination MUFA/PUFA increases with lowering body temperature (40-55% in cold-adapted organisms vs. 5-15% in warm adapted ones), signifying that this characteristic is probably in key position concerning regulation of membrane fluidity in temperature adaptation. According to this feature M. affinis belongs to the group of cold-adapted stenothermic species (Group 1) while eurythermic Gammarus spp. settles in the Group 2 (cold-acclimatized) or 3 (warm-acclimatized/tropical) depending on the status of temperature adaptation. Omnivory and/or periodical food item switching is an important strategy in benthic organisms in high-latitude areas characterised by recurring long poor-nutritional periods. Since many benthic species utilise a time-averaged, integrated food source from phytal and animal matter from various sources the FA composition of TAG of the amphipod species measured here do not exclusively point towards any specific feeding mode or food source. In general, using selected FA as food source markers to assess the diet of field collected more-or-less omnivoric species cannot be considered as an optimal approach. The current study gives more insight to the biochemistry of biological membranes of aquatic crustaceans that is essential in estimation of the capacity of the thermal adaptation/acclimatization of organisms as well as the potential effects of food quality on storage lipids.     

Benthic-pelagic interactions in shallow water columns: an experimentalist's perspective

Shallow water column benthic and pelagic communities are thought to be linked by trophic relationships, through life history or ontogenetic links, and by biologically or physically-mediated resuspension or sedimentation processes. It is often confusing and sometimes misleading to focus only on benthic or only on pelagic components of aquatic food webs, even though the literature on shallow water column experiments contains few experiments that give a balanced view of these components, or interactions between components in different habitats. The rarity of balanced experiments is especially troublesome because the most common types of manipulations in shallow water column experiments (fish and nutrients) often have rapid, direct effects on both kinds of habitats, or easily recognized indirect links between the two habitats that go unevaluated. Despite a large experimental literature on pelagic and benthic foodwebs (with less on both in the same systems), there appears to be continuing uncertainty about the importance to pelagic productivity of nutrients released from resuspended sediments, the role of macrobenthos in controlling plankton, and the efficacy and interaction of trophic cascades between pelagic and benthic communities.     

Spatial and Temporal Variability in the Ecosystem Metabolism of a High-elevation Lake: Integrating Benthic and Pelagic Habitats

We characterized spatial and temporal variability in net ecosystem production (NEP), community respiration (CR), and gross primary production (GPP) over an ice-free season in an oligotrophic high-elevation lake using high-frequency measurements of dissolved oxygen. We combined the use of free-water and incubation chamber measurements to compare pelagic and benthic habitats and estimate their relative contributions to whole-lake metabolism. Despite a brief period of predominant heterotrophy after snowmelt, both free-water and incubation chamber measurements confirmed autotrophy of the epilimnion in all habitats throughout the ice-free season. In contrast, benthic incubation chambers showed the benthos to be consistently heterotrophic. Although temperature was the strongest seasonal driver of benthic metabolism, bacterioplankton density and indexes of organic matter quality explained the most variability in pelagic metabolism. Driven largely by benthic metabolism, free-water measurements of GPP and CR were twice as high in littoral than pelagic habitats. However, rates of water column primary production overlying the littoral benthos were high enough to overcome net benthic heterotrophy, and seasonal mean NEP in littoral habitats remained positive and not significantly different from pelagic habitats. Benthic rates averaged about 25% of whole-lake metabolism. Pelagic metabolism measurements were affected by littoral rates about half the time, with the degree of isolation between the two a function of advection and water column stability. These results emphasize the importance of characterizing spatial and temporal variability in metabolism within the context of physical dynamics and challenge the notion that benthic metabolism will necessarily be larger than pelagic metabolism in oligotrophic lakes.     

Lifeform indicators reveal large‐scale shifts in plankton across the North‐West European shelf

Increasing direct human pressures on the marine environment, coupled with climate‐driven changes, is a concern to marine ecosystems globally. This requires the development and monitoring of ecosystem indicators for effective management and adaptation planning. Plankton lifeforms (broad functional groups) are sensitive indicators of marine environmental change and can provide a simplified view of plankton biodiversity, building an understanding of change in lower trophic levels. Here, we visualize regional‐scale multi‐decadal trends in six key plankton lifeforms as well as their correlative relationships with sea surface temperature (SST). For the first time, we collate trends across multiple disparate surveys, comparing the spatially and temporally extensive Continuous Plankton Recorder (CPR) survey (offshore) with multiple long‐term fixed station‐based time‐series (inshore) from around the UK coastline. These analyses of plankton lifeforms showed profound long‐term changes, which were coherent across large spatial scales. For example, ‘diatom’ and ‘meroplankton’ lifeforms showed strong alignment between surveys and coherent regional‐scale trends, with the 1998–2017 decadal average abundance of meroplankton being 2.3 times that of 1958–1967 for CPR samples in the North Sea. This major, shelf‐wide increase in meroplankton correlated with increasing SSTs, and contrasted with a general decrease in holoplankton (dominated by small copepods), indicating a changing balance of benthic and pelagic fauna. Likewise, inshore‐offshore gradients in dinoflagellate trends, with contemporary increases inshore contrasting with multi‐decadal decreases offshore (approx. 75% lower decadal mean abundance), urgently require the identification of causal mechanisms. Our lifeform approach allows the collation of many different data types and time‐series across the NW European shelf, providing a crucial evidence base for informing ecosystem‐based management, and the development of regional adaptation plans.     

Intraspecific stoichiometric variability and the ratio of nitrogen to phosphorus resupplied by zooplankton

1. An in situ experiment was carried out in a high-mountain oligotrophic lake (La Caldera) to quantify the specific release rates of ammonium and phosphorus in different phases of the seasonal succession of plankton. The zooplankton community was dominated by the calanoid copepod Mixodiaptomus laciniatus .
2. The rates of release of N and P (from non-detectable to 3.58 μg N mg^–1 DW h^–1 and from 0.26 to 2.29 μg P mg^–1 DW h^–1, respectively) and the N : P released ratio (not detectable to 4.77) fell within the range typical of oligotrophic lakes dominated by copepodite assemblages.
3. The values of the zooplankton N : P ratio (5 : 1 to 10 : 1 by weight) were lower than those established for other species of calanoids, and followed a well-established pattern of seasonal variation from year to year with higher values after ice thaw and lower values as individual size increased (ontogenetic development).
4. The elemental composition of the zooplankton depended on individual size, while the released N : P ratio was inversely related to the N : P ratio of the food. This pattern conforms to the predictions of the homeostasis theory of Sterner (1990).
5. A feedback regulation was established between the stoichiometric composition of the zooplankton, their food and the released N : P ratio that can help explain changes in pelagic community structure during the ice-free period.     

Intraspecific stoichiometric variability and the ratio of nitrogen to phosphorus resupplied by zooplankton

1. An in situ experiment was carried out in a high-mountain oligotrophic lake (La Caldera) to quantify the specific release rates of ammonium and phosphorus in different phases of the seasonal succession of plankton. The zooplankton community was dominated by the calanoid copepod Mixodiaptomus laciniatus .
2. The rates of release of N and P (from non-detectable to 3.58 μg N mg^–1 DW h^–1 and from 0.26 to 2.29 μg P mg^–1 DW h^–1, respectively) and the N : P released ratio (not detectable to 4.77) fell within the range typical of oligotrophic lakes dominated by copepodite assemblages.
3. The values of the zooplankton N : P ratio (5 : 1 to 10 : 1 by weight) were lower than those established for other species of calanoids, and followed a well-established pattern of seasonal variation from year to year with higher values after ice thaw and lower values as individual size increased (ontogenetic development).
4. The elemental composition of the zooplankton depended on individual size, while the released N : P ratio was inversely related to the N : P ratio of the food. This pattern conforms to the predictions of the homeostasis theory of Sterner (1990).
5. A feedback regulation was established between the stoichiometric composition of the zooplankton, their food and the released N : P ratio that can help explain changes in pelagic community structure during the ice-free period.     

Carbon and nitrogen stable isotopic inventory of the most abundant demersal fish captured by benthic gears in southwestern Iceland (North Atlantic)

Stable isotopes (δ¹³C and δ¹⁵N) were used to examine the origin of organic matter for the most representative demersal species of the SW Icelandic fishery, accounting for over 70% of landings of those species in the North Atlantic. Samples were collected during a 2-week period in early September 2004 from landings and directly during fishing cruises. Stable isotopes showed that particulate organic matter and sedimentary organic matter were at the base of the food web and appeared to fill two different compartments: the pelagic and the benthic. The pelagic realm was composed of only capelin and sandeel; krill and redfish occupied an intermediate position between pelagic and benthic realms; while anglerfish, haddock, cod and ling resulted as the true demersal species while tusk, rays and plaice were strongly linked to the benthic habitat.     

Fatty acids in anopheline mosquito larvae and their habitats

Larvae of the three important Central American malaria vectors, Anopheles albimanus, An. vestitipennis, and An. darlingi, are found in distinctly different habitats broadly defined by hydrology and aquatic vegetation, but little is known about the actual food quality and quantity of these habitats. Polyunsaturated fatty acids (PUFA) are of special interest, because mosquitoes require 20:5ω3 (EPA), 20:4ω6 (ARA), and 22:6ω3 (DHA) and without an adequate supply of these PUFAs they are not able to complete their life cycle. We collected samples of larvae and their corresponding habitats and analyzed their fatty acid (FA) composition to reveal if there are any species‐specific and habitat‐specific differences in FA composition, and if habitat FA differences can be linked to differences in the mosquito FA pattern and, ultimately, mosquito performance. We also assessed how FA of wild larvae compare to the laboratory‐reared larvae. Habitats were generally low in essential PUFAs and there were no significant differences among the FA composition of habitat samples. There were significant differences in FA composition of larvae. An. darlingi contained significantly higher amounts of FA, specifically a higher content of ω‐6 PUFA, represented mainly by the linoleic acid (18:2ω‐6). Large differences were found between field‐collected and laboratory‐reared An. vestitipennis larvae, especially in the content of PUFAs. The laboratory‐reared larvae contained significantly more of the total FA, ω3 PUFA, and MUFA. The laboratory‐reared larvae contained three to five times more essential PUFAs, EPA, and DHA. However, there were no differences in the total dry weight of the 4^th instar larvae between the wild vs laboratory‐reared larvae. Total FA in both larvae and habitats of An. albimanus and An. darlingi were positively correlated with the concentration of particulate organic carbon and nitrogen (POC, PON) in their respective habitats, but no such correlation was found for An. vestitipennis. PUFA are a good indicator of nutritional quality, although factors controlling the success of anopheline development from larval habitats are likely to be more complex and would include the presence of predators, pathogens, and toxins as interacting factors.     

Comparison of fatty acid composition in major lipid classes of the dominant benthic invertebrates of the Yenisei river

The composition and content of fatty acids (FAs) in total lipids, triacylglycerols (TAG) and polar lipids (PL) in dominant groups of benthic invertebrates: gammarids (Gammaridae, Amphipoda), chironomid larvae (Chironomidae, Diptera), caddisfly larvae (Trichoptera) and mayfly larvae (Ephemeroptera) were studied in the Yenisei river. For the first time data on the FA composition of species belonging to Trichoptera (Insecta) are presented. The groups of aquatic insect larvae and gammarids weakly differed in total content of essential polyunsaturated fatty acids (PUFAs). Hence, the strong invasion of gammarids which occurred in the last decades in the Yenisei river should not result in a decrease in potential yield of essential PUFA in the ecosystem and corresponding decrease in food resource quality for fish in respect to PUFA content. Significant differences in biomarker FAs in TAG were found which correlated to specific food sources. Different levels of long-chain PUFA in PL of the invertebrates are discussed in relation to the genetic ability of particular taxa to form these FAs.     

Polyunsaturated fatty acids in zooplankton: variation due to taxonomy and trophic position

1. Food quality has major effects on the transfer of energy and matter in food webs, and essential long‐chained polyunsaturated fatty acids (PUFAs) can affect the quality of phytoplankton as food. In a study of oligotrophic lakes in north‐western Sweden, we investigated the fatty acid composition of four planktonic cladocerans and two calanoid copepods, representing herbivorous and carnivorous species. We also collected seston samples. 2. The proportions of long‐chain PUFAs in the organisms increased with their increasing trophic position. Thus, both their quality as food for other organisms, as well as their requirement for fatty acids (FAs), differed among taxa and depended on their trophic position. 3. We found taxon‐specific differences in the FA composition of zooplankton that were not related to sestonic FA composition. This implies that the variation in zooplankton FA composition is constrained by phylogenetic origin, life history characteristics, or both. 4. The cladoceran taxa contained 12–23% eicosapentaenoic acid (EPA) but only 0.9–2.1% docosahexaenoic acid (DHA) of the total FA content. In contrast, the calanoid copepods contained 7–11% EPA and 14–21% DHA. Thus, our results show that differences in the PUFA content among zooplankton species could have repercussions for both food web structure and function.