Ontogenetic and seasonal changes in lipid and fatty acid/alcohol compositions of the dominant Antarctic copepods Calanus propinquus,Calanoides acutus and Rhincalanus gigas

Lipid compositions of the dominant Antarctic copepods Calanoides acutus, Rhincalanus gigas and Calanus propinquus from the Weddell Sea have been investigated in great detail. Copepods were collected during summer in 1985 and late spring/early winter in 1986. The analyses revealed specific adaptations in the lipid biochemistry of these species which result in very different lipid components. The various copepodite stages of C. acutus synthesize wax esters with long-chain monounsaturated moieties and especially the alcohols consisted mainly of 20:1(n-9) and 22:1(n-11). R. gigas also generates wax esters, but with moieties of shorter chain length. The fatty alcohols consisted mainly of 14:0 and 16:0 components, while the major fatty acids were 20:5, 18:4 and 22:6, of which 18:4 probably originated from dietary input. In contrast, C. propinquus accumulates triacylglycerols, a very unusual depot lipid in polar calanoid copepods. Major fatty acids in C. propinquus were the long-chain monounsaturates 22:1(n-9) and 22:1(n-11), which may comprise up to 50% of total fatty acids. In C. acutus and C. propinquus there was a clear increase of long-chain fatty acids with increasing developmental stage. In contrast, the fatty acid and alcohol composition of the R. gigas copepodite stages were characterized by the dominance of the polyunsaturated fatty acids as well as high amounts of the monounsaturates 18:1(n-9) and 16:1(n-7). There was a considerable decrease of the dietary fatty acid 18:4(n-3) towards the older stages during summer; in late winter/early spring 18:4 was only detected in very low amounts. This tendency was also found in the other two species, but was less pronounced. In all three species dry weight and lipid content increased exponentially from younger to older stages. The highest portion of wax esters, or of triacylglycerols in C. propinquus, was found in the adults. Dry weight and lipid content were generally higher during summer. In late winter/early spring the variability was more pronounced and lipid-rich specimens showed a selective retention of long-chain monounsaturated fatty acids, whereas in lipid-poor specimens these fatty acids were very much depleted.     

Feeding ecology and energetics of the Antarctic chaetognaths Eukrohnia hamata, E. bathypelagica and E. bathyantarctica

Ecological and physiological studies focused on dietary preferences, lipid biochemistry and energetics within the three Antarctic chaetognaths Eukrohnia hamata, E. bathypelagica and E. bathyantarctica from meso- and bathypelagic depths. Eukrohnia hamata and E. bathypelagica respired 0.15 μL O₂ mg dry mass (DM)⁻¹ h⁻¹, which translates to an average metabolic loss of only <1.1% of body carbon per day. Lipid storage was not substantial in E. bathypelagica (mean 11.5 ± 6.5% DM) and E. bathyantarctica (mean 15.4 ± 4.1% DM) during summer and winter, suggesting year-round feeding of these predators mainly on copepods. In E. bathypelagica, total fatty acids were dominated by the fatty acids 16:0, 20:5(n-3) and 22:6(n-3) and in E. bathyantarctica also by 18:1(n-9), a fatty acid usually found in storage lipids. Only the latter species was characterized by significant amounts of wax esters, consisting largely of the common fatty alcohols 16:0, 20:1(n-9) and the unusual fatty alcohol isomer 22:1(n-9).     

Fecundity,brood loss and egg development through embryogenesis of <Emphasis Type="Italic">Armases cinereum</Emphasis> (Decapoda: Grapsidae)

The present work is a comprehensive study of reproduction and embryonic development of Armases cinereum. Ovigerous A. cinereum (Bosc, 1802) females from Sebastian Inlet, Florida (9.88–19.4 mm CW) lay 2,000–12,000 eggs per brood, depending on their CW (mm): fecundity = 24.662 CW^1.9432. A. cinereum displayed significant brood loss through development (ca. 500 eggs per brood) independently from their CW (no senescence). However, since smaller females lay fewer eggs than larger ones, the percentage of eggs lost during embryonic development is greater in smaller females. The number of eggs carried on a later stage of development (potential fertility = 5.5593 CW^2.4417) is a more accurate estimate of the reproductive output and subsequent recruitment. Egg volume increased during development (64%, 0.025–0.041 mm³ or 0.36–0.43 mm of diameter, N = 270) and was strongly correlated with egg water content increase (19.21%, r = 0.89). Lipids, particularly fatty acids, seem to be the major energy source for embryonic development, decreasing 56.31 and 37.08% (respectively) during embryonic development; both are negatively correlated with egg volume (r = −0.90). The utilization of fatty acids through the different developmental stages of A. cinereum is presented. The most consumed fatty acids are the monounsatured (43.33 μg mg⁻¹ dw), followed by the saturated (29.91 μg mg⁻¹ dw) and polyunsaturated (24.03 μg mg⁻¹). Palmitic (16:0) and linoleic (18:2n-6) acids are preferentially consumed (19.5 and 17.9 μg mg⁻¹ dw, respectively). The high proportion of essential polyunsaturated fatty acids of C₁₈ and C₂₀ reflects the consumption of primary producers such as mangrove leaves. EPA/DHA ratio (2.85–3.84) and low DHA content indicated that this species appears in a medium-low level of the trophic chain. The low ratio of 18:1n-7/18:1n-9 and high percentage of 18:1n-9 (marker of carnivory) may be a sign of the consumption of juvenile invertebrates. The high percentage of odd-numbered FA indicated the occurrence of detritivores/scavenger behaviours. The fatty acid composition of the eggs reflects adult feeding ecology (omnivorous) and habitat.     

Mechanism(s) of long chain n-3 essential fatty acid production in two species of heterotrophic protists: <Emphasis Type="Italic">Oxyrrhis marina</Emphasis> and <Emphasis Type="Italic">Gyrodinium dominans</Emphasis>

As intermediaries, some heterotrophic protists can enhance the content of the long chain n-3 essential fatty acids (LCn-3EFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), of low food quality algae for subsequent use at higher trophic levels. However, the mechanisms that produce LCn-3EFAs are presently unknown, although LCn-3EFA production by heterotrophic protists at the phytoplankton–zooplankton interface may potentially affect the nutritional status of the pelagic system. We investigated whether the heterotrophic protists, Oxyrrhis marina and Gyrodinium dominans, produce LCn-3EFAs via elongation and desaturation of dietary LCn-3EFA precursors and/or synthesize LCn-3EFAs de novo by: (1) feeding the two heterotrophic protists with a prey deficient in n-3 fatty acids, (2) incubating them in medium containing ¹³C-labeled sodium acetate, and (3) feeding the two protists gelatin acacia microspheres (GAMs) containing a deuterium-labeled LCn-3EFA precursor, linolenic acid [18:3(n-3)-d4]. Both O. marina and G. dominans synthesized EPA and DHA when fed the n-3 fatty acid-deficient prey, Perkinsus marinus, a parasitic protozoan. O. marina, but not G. dominans utilized ¹³C-labeled acetate from the medium to produce uniformly labeled fatty acids, including DHA. Both heterotroph species consumed GAMs containing 18:3(n-3)-d4 and catabolized 18:3(n-3)-d4 to 16:3(n-3)-d4 and 14:3(n-3)-d4, while no 20 or 22 carbon metabolites of 18:3(n-3)-d4 were detected. These results suggest that O. marina and G. dominans do not elongate and desaturate dietary LCn-3EFA precursors to produce LCn-3EFAs, but rather they produce LCn-3EFAs de novo, possibly via a polyketide synthesis pathway.     

Characterizing dietary variability and trophic positions of coastal calanoid copepods: insight from stable isotopes and fatty acids

The spring zooplankton community in the Strait of Georgia (British Columbia, Canada) is characterized by the presence of several calanoid copepod species which collectively make up ~90% of the mezozooplankton biomass. Here, we investigate interspecific, interannual, and geographic variability in the diets and trophic positions of these copepods using a combination of fatty acids and stable isotopes. To characterize geographic variability in diet, we compare our findings from the Strait of Georgia with similar data from Ocean Station P in the subarctic northeast Pacific. Both fatty acid and stable isotope signatures indicate the existence of three trophic levels, even within the limited size range of these copepods: Neocalanus plumchrus and Calanus marshallae are primarily omnivorous, while Euchaeta elongata is carnivorous and Eucalanus bungii is herbivorous. Fatty acid markers of trophic position (e.g., DHA/EPA, 18:1n-9/18:1n-7) correlate significantly with δ¹⁵N, while markers indicating the proportion of diatoms to flagellates in the diet (e.g., 16PUFA/18PUFA and DHA/EPA) correlate significantly with δ¹³C, after the effect of lipid concentration on δ¹³C is accounted for. Despite the general correlation between stable isotopes and fatty acids, the former are not sensitive enough to capture the range of interannual variability observed in the latter, and can only capture substantial shifts in the diet over geographic scales. However, regardless of variability in food quality, the relative trophic positions of these copepods do not change significantly either spatially or temporally.     

On the lipid biochemistry of polar copepods: compositional differences in the Antarctic calanoids Euchaeta antarctica and Euchirella rostromagna

During austral summer of 1985 different developmental stages (CIII, CIV, CV, females, males) of the Antarctic copepod Euchaeta antarctica and females of Euchirella rostromagna were collected in the southeastern Weddell Sea to determine their lipid contents and compositions. For E. antarctica the analyses revealed a strong ontogenetic accumulation of lipids towards the older copepodids with highest lipid contents in late CV stages and adults. The females of E. rostromagna had moderate lipid levels. The most striking difference between these two species concerns their lipid class compositions. E. antarctica deposited predominantly wax esters, whereas in E. rostromagna the major lipid class consisted of triacylglycerols, an unusual storage lipid in polar marine copepods. Principal fatty acids in E. antarctica were the monounsaturates 18:1(n-9) and 16:1(n-7), especially in the lipid-rich stages, while the polyunsaturated fatty acids 20:5(n-3) and 22:6(n-3), usually membrane lipids, dominated in the lipid-poor stages. The wax ester moieties in E. antarctica consisted almost entirely of 14:0 and 16:0 fatty alcohols. Major components in E. rostromagna were the fatty acids 18:1(n-9), 16:0, 20:5(n-3) and 22:6(n-3). The potential of fatty acids and alcohols as typical trophic markers is rendered largely insignificant in the two species due to catabolic processes.     

Spatial variability in lipid composition of calanoid copepods from Fram Strait,the Arctic

The calanoid copepods Calanus hyperboreus and C. finmarchicus were investigated in view of their lipid and wax ester content and their fatty acid and alcohol composition. Analyses were performed in females and copepodid stages V and IV from the Fram Strait region between Greenland and Spitsbergen in 1984. This region offers different food conditions like diatom blooms in the North East Water Polynya, food shortage in areas with very close ice cover, high phytoplankton biomass in the marginal ice zone and lower biomass in the open Atlantic water. Lipids contained generally more than 70% wax esters. Highest levels were found in C. hyperboreus with more than 90%. This percentage was not very variable, in spite of large differences in dry weight and lipid content. Copepods with particularly high weight and lipid content were found in the North East Water Polynya. The lightest individuals were found under the pack ice. Lipid proportions per unit dry weight were higher in C. hyperboreus than in C. finmarchicus, whose lowest values were found in the open Atlantic water. Spatial variability in fatty acid composition was much higher than in alcohol composition. The principle alcohols, 20:1 and 22:1, generally accounting for more than 80% of total alcohols. In the North East Water Polynya, the predominant monounsaturated fatty acid was 16:1, while under the ice 20:1 and 22:1 dominated. In the marginal ice zone and in the open water, the 18:4 acid reached percentages up to 30% of total fatty acids. These changes were related to the different food conditions. C. hyperboreus appears to be best adapted to the cold water and unfavourable conditions of polar regions because of its high lipid and wax ester store with long-chain wax esters of high calorific value.     

Egg production and feeding by copepods prior to the spring bloom of phytoplankton in Fram Strait,Greenland Sea

Reproductively activeCalanus hyperboreus (Krøyer) andC. glacialis Jaschnov were captured in the upper 100 m of Fram Strait (77° to 79°N) in late winter 1987. There was no evidence of a phytoplankton bloom; chlorophylla concentrations were uniformly low (<0.1 mg m^–3), and nitrate concentrations were uniformly high (>11.3 mg-at m^–3). Gut-fullness measurements indicated that females were ingesting very little. The maturation state of gonads of bothC. hyperboreus andC. glacialis indicated that 75% of females were in a ripe condition consistent with observed egg laying. The lipid content of females laying eggs was reduced in both species compared to that of females not laying eggs. InC. hyperboreus the reduction was 39% and inC. glacialis it was 44%. All the evidence suggests that bothC. hyperboreus andC. glacialis were laying eggs in late winter by using lipids stored previously; they were not relying on ambient concentrations of phytoplankton. The daily rate of egg laying byC. glacialis using lipids in late winter exceeded the rate reported for summer when ambient food supplies have been shown to be necessary. It is suggested that individuals, spawned well in advance of the spring bloom of phytoplankton, may comprise a major portion of the annual recruitment to the entire population ofC. glacialis in this area, and that their life cycle can be completed within 1 yr. NeitherMetridia longa (Lubbock) norC. finmarchicus (Gunnerus) laid eggs during this study.     

The Arctic sea butterfly<Emphasis Type="Italic"> Limacina helicina</Emphasis>: lipids and life strategy

The sea butterfly Limacina helicina was collected from May to September 2001 in Kongsfjorden, Spitsbergen, to investigate population structure and body and lipid composition with regard to life cycle and reproductive strategy. Veligers and juveniles were only found in late autumn and spring, whereas females occurred from July to September. The size of the females increased until mid-August and decreased in September. Dry and lipid mass were closely related to size; dry mass increased exponentially and lipids linearly with size. The lipid content was highest in veligers (31.5% of dry mass) and juveniles (23.6%) but low in females (<10%). Phospholipids were the dominating lipid class followed by triacylglycerols. Females, veligers, and egg ribbons, all from September, were richest in phospholipids. Juveniles contained the highest amounts of triacylglycerols, whereas females had low levels in July and the beginning of August. In mid-August, levels of triacylglycerols were variable and higher. This suggests that females were in their main spawning period and the high variability in triacylglycerols points to different stages within the spawning cycle. Enhanced amounts of free fatty acids in females from July may be related to gonad development. The 16:1(n-7) fatty acid was more dominant in spring whereas 18:4(n-3) increased in summer and autumn, which reflects a change in diet from diatom-dominated food items in spring to dinoflagellates in summer/autumn. Small amounts of long-chain monounsaturated fatty acids suggest ingestion of copepods, and the fatty acid composition of veligers feeding on particulate matter. L. helicina has a one-year life cycle with peak spawning in August and over-winters as veligers that may grow to juveniles during the winter period. They metamorphose into juveniles during spring, develop to males in early summer, and mature into females in July and August.Communicated by M. Kühl, Helsingør     

Fatty acid composition of organs and tissues of the tiger prawn Penaeus esculentus during the moulting cycle and during starvation

The fatty acids (FA) in neutral lipid (NL) and polar lipid (PL) of digestive gland, muscle and integument of Penaeus esculentus Haswell were analysed and compared during the moulting cycle and during starvation. The prawns were collected from Moreton Bay, Queensland, Australia, by trawling during 1985–1987, and were fed with a standard semi-purified diet. Compared with a natural diet, the artificial diet had much higher levels of 18:1n-9 and 18:2n-6, but only trace amounts of 20:4n-6, but there was no evidence of dietary imbalance. The fatty acid composition (percentage of total lipid) of the digestive gland changed markedly during the moulting cycle and during starvation, but the small changes observed in both muscle and integument suggested that these tissues maintained their composition under both conditions. When the fatty acids were calculated as absolute amounts, muscle composition, as well as that of the digestive gland, changed significantly. In the digestive gland, saturated FA (SFA), monounsaturated FA (MUFA), diunsaturated FA (DUFA) and polyunsaturated FA (PUFA) all increased up to the middle of the moulting cycle and then declined; with starvation all groups decreased. In muscle, SFA, MUFA and DUFA all increased during the moulting cycle; starvation caused SFA, MUFA and PUFA to decrease, whereas DUFA did not vary. Starvation caused both 18:2n-6 (linoleic) and 18:3n-3 (linolenic) in the digestive gland to reach or almost reach zero. The other essential PUFA, 20:4n-6 (arachidonic), 20:5n-3 (eicosapentaenoic) and 22:6n-3 (docosahexaenoic), decreased during the moulting cycle, but during starvation 20:4n-6 did not decrease as much. In muscle, the levels of 18:2n-6 and 18:3n-3 increased, while 20:4n-6, 20:5n-3 and 22:6n-3 remained approximately constant during the moulting cycle. Starvation reduced 20:5n-3 and 22:6n-3 to about 60%. The data suggest that levels of 18:3n-3, 20:4n-6, 20:5n-3 and 22:6n-3 are regulated, and that 20:4n-6 can be synthesised from 18:2n-6. There is no clear evidence that 20:5n-3 and 22:6n-3 are essential in P. esculentus, but tissue catabolism of cell membranes during starvation may have provided sufficient amounts for maintenance.     

Lipid storage and composition in tropical surgeonfishes (Teleostei: Acanthuridae)

The lipid composition of tropical marine reef fishes is poorly known, despite their use as food by local human populations and recent interest in health-related benefits of fish lipids. We examined the composition of lipids from epaxial muscle, liver, and two storage sites [mesenteries surrounding the gut (intraperitoneal fat, IPFs) and retroperitoneal fat bodies (FBs) posterior to the peritoneal cavity] in three species of surgeonfishes from Ishigaki Island, Japan: Naso lituratus (Bloch and Schneider, 1801), Acanthurus lineatus (Linnaeus, 1758), and A. bariene (Lesson, 1830). Triacylglycerols dominated all samples of neutral lipid and constituted ≥ 99% of FBs and IPFs. Polar lipids generally contained large fractions of phosphatidylethanolamine and phosphatidylcholine. Quantified fatty acids ranged in length from C₁₄ to C₂₄. C₁₆ fatty acids prevailed (>35% of neutral fatty acids, >23% of polar fatty acids), although C₁₈ (>16 and >14%, respectively) and C₂₀ acids (>8 and >19%, respectively) were also common. Saturated fatty acids, dominated by palmitic acid (16:0), comprised 38.7 to 50.7% of acids from neutral lipids and 30.8 to 41.1% from polar lipids. The most common monounsaturated acids were 18:1n9 and 20:1n9. Polyunsaturated acids were prevalent in polar lipids (especially 20:4n6, 20:5n3, 22:2n3, 22:5n3, 22:5n6 and 22:6n3). Common polyunsaturated acids of neutral lipids were 18:2n6, 18:4n3, several n-3 and n-6 C₂₀ acids, 22:2n3 and 22:5n3. IPF and FB were almost identical across species, and lipids of fat bodies (IPFs, FBs) were more similar to those of muscle than those of liver for all three species. The FBs appear to constitute an accessory storage site, which overcomes constraints on lipid storage imposed by a small, inflexible abdominal cavity that contains both viscera and consistently voluminous gut contents. Fatty acid signatures indicate that largely overlooked epiphytic or epilithic diatoms contribute significantly to lipid acquisition. The combination of large quantities of both saturated and n-3 and other polyunsaturated fatty acids in surgeonfishes, in contrast to low saturates and high polyunsaturated acids in lipids of commercially important cool-water fishes, suggests that a study of dietary effects of fish lipids on human inhabitants of the tropics may be instructive insofar as human health and nutrition are concerned. Received: 16 March 1998 / Accepted: 6 August 1998     

Seasonal lipid dynamics of the copepods <Emphasis Type="Italic">Pseudocalanus minutus</Emphasis> (Calanoida) and <Emphasis Type="Italic">Oithona similis</Emphasis> (Cyclopoida) in the Arctic Kongsfjorden (Svalbard)

Seasonal lipid dynamics of various developmental stages were investigated in Pseudocalanus minutus and Oithona similis. For P. minutus, the dominance of 16:1(n−7), 16:4(n−3) and 20:5(n−3) fatty acids indicated a diatom-based nutrition in spring, whereas 22:6(n−3), 16:0, 18:2(n−6) and 18:1(n−9) pointed to a flagellate-based diet during the rest of the year as well as omnivorous/carnivorous low-level feeding during winter. The shorter-chain fatty alcohols 14:0 and 16:0 prevailed, also reflecting biosynthetic processes typical of omnivores or carnivores. Altogether, the lipid signatures characterized P. minutus as an opportunistic feeder. In contrast, O. similis had consistently high amounts of the 18:1(n−9) fatty acid in all stages and during all seasons pointing to a generally omnivorous/carnivorous/detritivorous diet. Furthermore, the fatty alcohol 20:1(n−9) reached high percentages especially in adult females and males, and feeding on Calanus faecal pellets is suggested. Fatty alcohols, as wax ester moieties, revealed significant seasonal variations in O. similis and a seasonal trend towards wax ester accumulation in autumn in P. minutus. P. minutus utilized its lipid deposits for development in the copepodite stages III and IV and for gonad maturation in CV and females during the dark season. However, CVs and females depended on the spring phytoplankton bloom for final maturation processes and reproduction. O. similis fueled gonad maturation and egg production for reproduction in June by wax esters, whereas reproduction in August/September co-occurred with the accumulation of new depot lipids. Both species revealed significantly higher wax ester levels in deeper (>50 m) as compared to surface (0–50 m) dwelling individuals related to a descent prior to overwintering.     

Spatial and temporal variation in the elemental and stable isotopic content of the seagrasses <Emphasis Type="Italic">Posidonia oceanica</Emphasis> and <Emphasis Type="Italic">Cymodocea nodosa</Emphasis> from the Illes Balears,Spain

Morphology, elemental content and isotopic composition of leaves of the seagrasses Posidonia oceanica and Cymodocea nodosa were highly variable across the Illes Balears, a Spanish archipelago in the western Mediterranean, and varied seasonally at one site in the study area. The data presented in this paper generally expand the reported ranges of nitrogen, phosphorus, iron and arsenic content and δ¹³C and δ¹⁵N for these species. Nitrogen and phosphorus content of P. oceanica leaves also showed significant seasonal variability; on an annual basis, P. oceanica leaves averaged 1.55% N and 0.14% P at this monitoring site. Both N and P were more concentrated in the leaves in winter than in summer, with winter maxima of 1.76% N and 0.17% P and summer minima of 1.34% N and 0.11% P. There was no significant annual pattern observed in the δ¹³C of P. oceanica leaves, but there was a repeated 0.6‰ seasonal fluctuation in δ¹⁵N. Mean annual δ¹⁵N was 4.0‰; δ¹⁵N was lowest in May and it increased through the summer and autumn to a maximum in November. Over the geographic range of our study area, there were interspecific differences in the carbon, nitrogen and phosphorus content of the two species. Posidonia oceanica N:P ratios were distributed around the critical value of 30:1 while the ratios for C. nodosa were lower than this value, suggesting P. oceanica we collected was not consistently limited by N or P while C. nodosa tended toward nitrogen limitation. Nutrient content was significantly correlated to morphological indicators of plant vigor. Fe content of P. oceanica leaves varied by a factor of 5×, with a minimum of 31.1 μg g⁻¹ and a maximum of 167.7 μg g⁻¹. Arsenic was present in much lower tissue concentrations than Fe, but the As concentrations were more variable; the maximum concentration of 1.60 μg g⁻¹ was eight times as high as the minimum of 0.20 μg g⁻¹. There were interspecific differences in δ¹³C of the two species; C. nodosa was consistently more enriched (δ¹³C = −7.8 ± 1.7‰) than P. oceanica (−13.2 ± 1.2‰). The δ¹³C of both species decreased significantly with increasing water depth. Depth related and regional variability in the δ¹³C and δ¹⁵N of both species were marked, suggesting that caution needs to be exercised when applying stable isotopes in food web analyses.     

Fatty acid composition as a dietary indicator of the invasive caprellid, Caprella mutica (Crustacea: Amphipoda)

The invasive caprellid amphipod Caprella mutica is one of the most widely dispersed marine non-native species globally. Originating in sub-boreal north-east Asia, it has now been found in both the northern and the southern hemispheres. One potential reason why this species is such a successful invader is its ability to utilise a wide variety of food sources. The contribution of different food sources to the diet of C. mutica was estimated using fatty acids as biomarkers. Caprella mutica was collected from three field sites, including sea cages stocked with Atlantic salmon Salmo salar, shellfish longlines stocked with the blue mussel Mytilus edulis and mooring lines marking the Loch Linnhe Artificial Reef (>2 km from caged finfish aquaculture), where established populations of this species are known to occur. In addition, the fatty acid compositions of C. mutica held in aquaria and either fed the microalga, Dunaliella tertiolecta, or the diatom, Phaeodactylum tricornutum, for a period of 21 days were investigated. The fatty acid composition of the diatom and the microalgal diets was also examined. The results showed that C. mutica contained high levels of polyunsaturated fatty acids, particularly 20:5(n-3); other dominant fatty acids included 18:1(n-9), 22:6(n-3) and 16:0 (in decreasing order based on abundance). Significant differences in the fatty acid profiles between caprellids fed on the microalgae and the diatom diets and between C. mutica collected from the field sites were observed. These results provide evidence that lipid biomarkers can be successfully used to provide evidence of feeding strategy for C. mutica and that the flexibility observed in this strategy may play an important role in its invasion success.     

Lipid metabolism of the Antarctic krill Euphausia superba and its ecological implications

 Various developmental stages (early larvae to adults) of Euphausia superba have been collected in different seasons in the Weddell Sea, the Lazarev Sea and off the Antarctic Peninsula to investigate the role of lipids and fatty acids in the life cycle of the Antarctic krill. The total-lipid data for E. superba exhibited seasonal variations, with low lipid levels in late winter/early spring and the highest levels in autumn. Seasonal changes were most pronounced in the immature and adult specimens, increasing from about 10% lipid of dry mass to more than 40%. The fatty-acid compositions of the younger stages were dominated by 20:5(n-3), 22:6(n-3) and 16:0. These are typical phospholipid fatty acids, which are major biomembrane constituents. The phospholipid composition was similar in the older stages. With increasing storage of triacylglycerols in the lipid-rich immature and adult stages, the fatty acids 14:0, 16:0 and 18:1(n-9) prevailed, comprising about 70% of total triacylglycerol fatty acids. The trophic-marker fatty acids 16:1(n-7) and 18:4(n-3), indicating phytoplankton ingestion, were less abundant. They reflected, however, the dependence of the larvae on phytoplankton as well as the seasonal changes in algal composition. The generally close linear relationships between fatty acids and lipid suggest that the fatty-acid compositions of the collected specimens were largely independent of the respective developmental stage, season and region. The linear fit indicates that triacylglycerol accumulation started at a level of about 5% of total lipid. Considering the various overwintering scenarios under discussion, the life cycle and reproductive strategies of krill are discussed in the context of the lipid metabolism and fatty-acid composition of E. superba. Lipid production is effective enough to accumulate large energy reserves for the dark season, but E. superba does not exhibit the sophisticated biosynthetic pathways known from other Antarctic euphausiids and copepods. Although important, lipid utilisation appears to be just one of several strategies of E. superba to thrive under the extreme Antarctic conditions, and this pronounced versatility may explain the success of this species in the Southern Ocean. Received: 16 June 2000 / Accepted: 18 December 2000     

Identifying trophic relationships within the high Arctic benthic community: how much can fatty acids tell?

Multivariate analysis of fatty acids (FA) profiles proved to be a useful tool for demonstrating feeding preferences of Arctic invertebrates belonging to several taxonomic groups collected during summer and winter seasons in the Spitsbergen fjords (Arctic). Within phytodetrivorous taxa, the enhanced proportions of 16:1n-7, C16 polyunsaturated fatty acids (PUFA) and 20:5n-3 in crustaceans clearly reflected selective ingestion of diatoms, while high amounts of 22:6n-3 and C18 FAs found in molluscs indicated flagellate-based nutrition. High levels of C20 PUFA and 16:1n-7 together with the typical bacterial FAs were found in winter specimens of deposit-feeding polychaetes showing their reliance on highly reworked organic matter during this season. Our results suggest that 18:1n-9 may not be a reliable marker of carnivory feeding within benthic taxa. Lipid signatures of omnivores and carnivores/detrivores usually originated from a variety of dietary sources, of which few possess highly characteristic FA features. Still, elevated levels of Calanus markers (20:1 and 22:1 moieties) characterized species linked to the pelagic food chains, while 20:4n-6 proved to be a useful indicator of foraminiferan consumption. We highlight the need for a multimethod approach, since complexity of benthic food webs along with general lack of unambiguous FA trophic markers prevents tracking of trophic relationships with use of FA analysis alone. Based on their FA composition, we showed that benthic species represent a source of essential PUFA and could play a fundamental role in the Arctic food webs transferring energy derived from variable pelagic and benthic resources to upper trophic levels.     

Life cycle of the copepod Calanus hyperboreus in the Greenland Sea

The seasonal ontogenetic migration of the Arctic copepod Calanus hyperboreus was described from surface-to-bottom hauls in the central Greenland Sea Gyre (GSG) and in the Westspitsbergen Current (WSC). All stages except females spent the winter below 500 m in the GSG and below 1000 m in the WSC. Seasonal ascent begins in April, and descent in July. For the C.␣hyperboreus population an active downward transport of 8.1 g m⁻² dry weight during 8 months of overwintering was estimated, similar to flux rates of particulate matter in sediment traps. Seasonal distribution of biomass was determined from weight measurements of single stages. Annual means varied from 4.0 to 9.2 g m⁻² in two different years in the GSG and were 1.1 in 1 year in the WSC. The life cycle in the Greenland Sea was reconstructed from field data on stage composition, vertical distribution, reproduction, and moult cycle phase from tooth development of CV. Laboratory experiments were conducted on the moulting of CIV and CV in fall. A 3-year (males) and 3- to 4-year (females) life cycle is proposed for the GSG and 2 to 3 years for the WSC. However, the small number of young larvae and the incomplete spring ascent by older copepodites observed in the WSC cast doubt on the reproductive success in the WSC. A suite of physiological strategies and adaptations performed by the developmental stages support survival of this species in harsh environments. Received: 25 January 1997 / Accepted: 11 February 1997     

Seasonal variations of ATPase activity and antioxidant defenses in gills of the mud crab <Emphasis Type="Italic">Scylla serrata</Emphasis> (Crustacea,Decapoda)

The mud crab Scylla serrata is an important commercial crustacean being widely distributed along the southeastern coast of China. This crab and particularly its gills are subjected to seasonal fluctuations of environmental factors due to direct exposure to seawater. The investigation of seasonal variations of ATPase and antioxidant defenses in gills could be helpful for the understanding of physiological regulation mechanism of seasonal adaptations. In this study, mud crabs were collected from the subtropical waters near Xiamen island, Southeast China (24°26′46′′N, 118°04′04′′E), in August and November, 2002, and February and May, 2003, respectively, being considered as specimens from summer, autumn, winter and spring, respectively. Only healthy intermoult male crabs without carapace or appendage damage were used, having a carapace width of 7.05 ± 0.52 cm and a wet weight of 130 ± 20 g. The activities of four ATPases and three antioxidation enzymes (superoxide dismutase, catalase, glutathione peroxidase) and the content of malondialdehyde in gills were measured. The results showed that the activities of Na⁺, K⁺-ATPase, Mg²⁺-ATPase, Ca²⁺-ATPase and Ca²⁺, Mg²⁺-ATPase reached maximum levels similarly in summer and decreased in winter. The activities of superoxide dismutase and catalase were higher in summer and lower in winter, with a significant decrease in winter compared to the other seasons (p < 0.01). Glutathione peroxidase activity was higher in summer, and lower in autumn, being significantly higher in summer or winter than in spring or autumn (p < 0.01). Malondialdehyde content was higher in summer and lower in spring with significant differences among the different seasons (p < 0.01). In summary, the obvious seasonal activity variations of four ATPases and antioxidant enzymes and the content of malondialdehyde reflect a seasonal regulation of the physiological metabolising enzyme and the antioxidant capacity to cope with seasonal alterations of environment factors such as fluctuating salinities and temperatures.     

Distribution and abundance of ctenophores and their zooplankton food in the Black Sea. II. Mnemiopsis leidyi

The distribution of Mnemiopsis leidyi Agassiz, 1865 in the Black Sea was determined using plankton samples collected above the anoxic zone (maximum depth 200 m) in the summer, winter, and spring from 1991 to 1995. Distribution was patchy. Average biomasses of 15 to 500 g m⁻² were measured, and abundances varied from 10 to 180 ind m⁻². Biomass and abundance peaked in winter, and there was a secondary peak in the summer. The distribution of M. leidyi was correlated with hydrographic features in the Black Sea with higher concentrations in anticyclonic gyres. The centers of the two main cyclonic gyres generally had a low biomass of M. leidyi. From July 1992 to March 1995, the populations were largely offshore. M. leidyi were confined to the upper part of the mixed layer both day and night. Some individuals displayed a negative taxis to daylight and were concentrated below the thermocline at night. Smaller M. leidyi (1.5 to 2 cm) were present in the winter, and individuals reached maximum size in the summer. Although reproduction was continuous throughout the year, there were two distinct peaks: the larger peak in the summer and the smaller peak in the winter. Microscopic analysis of stomach contents showed that copepods and molluscs form their main diet. Received: 1 November 1997 / Accepted: 30 August 1999     

Ontogenic variations in fatty acid and alcohol composition of the pelagic amphipod <Emphasis Type="Italic">Themisto libellula</Emphasis> in Kongsfjorden (Svalbard)

The fatty acid and alcohol composition of the pelagic amphipod, Themisto libellula, was monitored during the 5 first months of its life cycle (4–20 mm length) in an Arctic fjord, Kongsfjorden, Svalbard. Fatty acids of the three major lipid classes, polar lipids (PL), triacylglycerol (TAG), and wax esters (WE), were analyzed to highlight ontogenic changes in their diet and metabolism. The PL composition of T. libellula did not show any strong variations along their growth except during the first month where an important increase of 20:5(n-3) (EPA) and 22:6(n-3) (DHA) was observed. The TAG composition revealed a clear gradient corresponding to a diet shift from omnivorous juveniles toward carnivorous sub-adults and adults. Indeed, fatty acid trophic markers of diatoms were dominant in the juveniles, whereas 20:1(n-9) and 22:1(n-11), the Calanus sp. trophic markers, overwhelmed in the older stages. The WE composition highlighted the same general trend, however, differences were found with the TAG and are discussed as a result of differences in turnover rates and assimilation pathways between the two lipid classes.