Patti Virtue

Lipids and trophodynamics of Antarctic zooplankton

Abstract Zooplankton were collected by trawl from the Elephant Island region of the Antarctic Peninsula and from East Antarctica near 63–65°S and 139–150°W. Most zooplankton had low percentages of wax esters (0–8%, as percent of total lipid). High triacylglycerol levels were found in the hyperiid amphipod Themisto gaudichaudii (68%, as percent of total lipid), the krill (Euphausiacea) Euphausia tricantha (44–54% triacylglycerol) and Euphausia frigida (27% triacylglycerol) and the scyphomedusan Periphylla periphylla ( 42–48% triacylglycerol). Polyunsaturated fatty acids (PUFA) comprised 23–60% of the total fatty acids, with the omega-3 fatty acids eicosapentaenoic acid [20:5(n-3)] and docosahexaenoic acid [22:6(n-3)] being most abundant. P. periphylla was an exception with 12–19% docosapentaenoic acid [22:5 (n-3)] being the major PUFA. The major euphausiid sterols included cholesterol (75–92%, as percent of total sterols) and desmosterol (6–22%). The major sterols of other zooplankton were more diverse and included trans -dehydrocholesterol, 24-methylenecholesterol, brassicasterol and 24-nordehydrocholesterol. The benthic ascidian, Distaplia cylindrica , had 45% stanols, as percent of total sterols, whereas the pelagic ascidian Salpa thompsonii had only 8–11% stanols. Lipid, fatty acid and sterol data are used to examine trophodynamic interactions and provide an ability to distinguish herbivorous and carnivorous diets and determine survival and reproductive strategies.

Will krill fare well under Southern Ocean acidification

Antarctic krill embryos and larvae were experimentally exposed to 380 (control), 1000 and 2000 µatm pCO2 in order to assess the possible impact of ocean acidification on early development of krill. No significant effects were detected on embryonic development or larval behaviour at 1000 µatm pCO2; however, at 2000 µatm pCO2 development was disrupted before gastrulation in 90 per cent of embryos, and no larvae hatched successfully. Our model projections demonstrated that Southern Ocean sea water pCO2 could rise up to 1400 µatm in krills depth range under the IPCC IS92a scenario by the year 2100 (atmospheric pCO2 788 µatm). These results point out the urgent need for understanding the pCO2-response relationship for krill developmental and later stages, in order to predict the possible fate of this key species in the Southern Ocean.

Perspectives on marine zooplankton lipids

We developed new perspectives to identify important questions and to propose approaches for future research on marine food web lipids. They were related to (i) structure and function of lipids, (ii) lipid changes during critical life phases, (iii) trophic marker lipids, and (iv) potential impact of climate change. The first addresses the role of lipids in membranes, storage lipids, and buoyancy with the following key question: How are the properties of membranes and deposits affected by the various types of lipids? The second deals with the importance of various types of lipids during reproduction, development, and resting phases and addresses the role of the different storage lipids during growth and dormancy. The third relates to trophic marker lipids, which are an important tool to follow lipid and energy transfer through the food web. The central question is how can fatty acids be used to identify and quantify food web relationships? With the fourth, hypotheses are presented on effects of global warmi...

Reproductive trade-off in male Antarctic krill, Euphausia superba

Freshly caught male and female Euphausia superba from the same swarm exhibited different rates of mortality subsequent to capture. Mortality was significantly higher for reproductive males (100%, n=68) than for females (3%, n=186) within the first 3 d of capture. Total lipid and triacylglycerol levels in male, female and juvenile Euphausia superba were analysed and compared. All reproductive male krill analysed from this swarm had low lipid levels (1 to 3% dry weight) with negligible triacylglycerol stores (0 to 2% of total lipid). Somatic lipid stores in female and juvenile krill ranged from 8 to 30% of which up to 40% was triacylglycerol. The levels of algal sterols in the digestive gland of males, females and juveniles indicate that all krill had been feeding recently. An analysis of the sex ratio of krill catches derived from data collected over seven summers from the Prydz Bay region showed a decrease in the proportion of males with increasing size. There was a sharp decline in numbers of male krill once they attained a length of 51 to 55 mm. Low lipid levels in redroductive male krill may be due to reproductive costs. The resulting low storage-lipid levels are accompanied by high mortality in male krill.

Combined effects of two ocean change stressors, warming and acidification, on fertilization and early development of the Antarctic echinoid Sterechinus neumayeri

The effects of concurrent ocean warming and acidification on Antarctic marine benthos warrant investigation as little is known about potential synergies between these climate change stressors. We examined the interactive effects of warming and acidification on fertilization and embryonic development of the ecologically important sea urchin Sterechinus neumayeri reared from fertilization in elevated temperature (+1.5°C and 3°C) and decreased pH (−0.3 and −0.5 pH units) treatments. Fertilization using gametes from multiple males and females, to represent populations of spawners, was resilient to acidification at ambient temperature (0°C). At elevated temperatures, there was a negative interactive effect of temperature and pH on percentage of fertilization (11% reduction at 3°C). For cleavage stage embryos, there was a significant, but small reduction (6%) in the percentage of normal embryos at pH 7.5. For blastulae, a 10–11% decrease in normal development occurred in the +3°C treatments across all pH levels. Our results highlight the importance of considering the impacts of both temperature and pH in assessing the life history response of S. neumayeri in a changing polar ocean. While fertilization and development to the blastula stage were robust to levels of temperature and pH change predicted over coming decades, deleterious interactive effects were evident between these stressors at levels projected to occur by 2100 and beyond.

Changes in the digestive gland of Euphausia superba during short-term starvation: lipid class, fatty acid and sterol content and composition

During a period of short-term (19 d) starvation, total lipid in the digestive gland of Euphausia superba Dana decreased from 21 to 9% dry weight. Total lipid per digestive gland decreased significantly during starvation compared to Day 0 individuals, falling from 1960 (±172) to 385 (±81) μg. Polar lipid was the major lipid class utilised during starvation, falling from 1510 (±225) to 177 (±46) μg per digestive gland (76 to 45%). Absolute levels of triacylglycerol fell from 300 (±41) to 76 (±5) μg; however, relative levels remained unchanged. The relative level of free fatty acid increased significantly with starvation (4 to 39%) with absolute levels ranging from 79 (±1) to 156 (±20) μg per digestive gland. Absolute levels of all fatty acids per digestive gland declined continually until the end of the starvation period. The long-chain polyunsaturated acids eicosapentaenoic (20:5ω3) and docosahexaenoic (22:6ω3), decreased with starvation from 37 to 26% and 15 to 10%, respectively whereas the saturated fatty acid, palmitic acid (16:0), increased from 15 to 20%. Cholesterol, the major sterol in this organ, increased from 17 (±20) to 44 (±13) μg per digestive gland by Day 3, and by Day 19 had returned to levels found in the digestive gland of Day 0 individuals. Desmosterol followed a similar pattern to cholesterol, increasing from 3 (±1) μg per digestive gland on Day 0 to 11 (±4) μg on Day 3, and falling to 2 (±1) μg on Day 19. Other sterols in the digestive gland, predominantly of algal origin, fell from the levels found in Day 0 individuals to near zero amounts by Day 6. The digestive gland of E. superba plays a dynamic role during shortterm starvation in terms of lipid content and composition. The relative levels of polar lipids, free fatty acids and cholesterol in the digestive gland may provide reliable indices of the nutritional condition of E. superba in the field. Sterols in the digestive gland are indicative of recent dietary composition of krill, and may also be used to quantify dietary input from individual phytoplanktonic species.

The lipid composition of Euphausia superba Dana in relation to the nutritional value of Phaeocystis pouchetii (Hariot) Lagerheim

The fatty acid profiles ofEuphausiusuperba, the Antarctic prymnesiophyte, Phaeocystispouchetii, and a temperate diatom, Phaeodactylum tricornutum were analysed and compared. The lipid content, lipid class, fatty acid and sterol composition ofE. superba fed on each cultured phytoplankton and amixed diet ofboth species, were determined. No significant difference was found between total lipid levels of E. superba reared on each of these different diets. Phaeocystispouchetii, although deficient in a number of the essential fatty acids, is apparently an adequate food source for E. superba. The proportion of polyenoic fatty acids varied within lipid classes although there was no significant difference between levels of the long chain polyunsaturate 20:5(n-3) in the total lipid of E. superba fed on these diets. This acid was found to be less than 1% of the total lipid in Phaeocystispouchetii compared to 37% in Phaeodactyhm tricornutum. This suggests that krill may possess the ability to convert exogenousshorter chainfatty acids to 20:5(n-3) and 22:6(n-3). Significantdifferencesweredetectedin theisomeric ratio of 16:1(n-7~)/16:0b etween krill fed the diatom compared to the prymnesiophyte diet. Significant differences were also detected in several shorter chain fatty acids and between fatty acids within their lipid classes. Such differences may have the potential to be used as biochemical signatures to provide information on food sources and possible feeding grounds of E. superba. Phaeocystispouchetii in a very late stationary phase, although not used in this feeding study, was found to contain 11 % of 22:6(n-3) for which there are few substantive sources in natural algal populations.

Lipids and buoyancy in Southern ocean pteropods.

The lipids of Clione limacina, a Southern Ocean pteropod (order Gymnosomata), contain 28% diacylglyceryl ether (DAGE) (as percentage of total lipid) whereas the pteropod Limacina helicina (order Thecosomata) lacks DAGE. The alkyl glyceryl ether diols (1-O-alkyl glycerols, GE) of Clione DAGE are dominated by 16∶0 (60%) and 15∶0 (21%), in contrast with deep-sea shark liver DAGE, which is dominated by 18∶1 GE. The fatty acid profiles of Clione and Limacina are similar (28–32% polyunsaturated, 26–34% monounsaturated) as are the sterols, which include 24-methylenecholesterol, transdehydrocholesterol, cholesterol, and desmosterol. This finding probably reflects the fact that Limacina is the major food source for Clione. Spongiobranchaea australis, another Southern Ocean pteropod (order Gymnosomata), has 0.9–1.7% DAGE, but has less lipid (3.3–4.8 mg/g lipid, wet weight) than Clione (50.8 mg/g lipid, wet weight). We propose a buoyancy role for DAGE in Clione since Limacina has bubbles for flotation which Clione lack; DAGE provides 23% more uplift than triacylglycerol at a concentration of 1.025 g/mL seawater.

Simultaneous estimation of microbial phospholipid fatty acids and diether lipids by capillary gas chromatography

The simultaneous measurement ofspecific phospholipid ester-linked fatty acids (PLFA) and diether lipids was achieved using high temperature capillary gas chromatography (GC). A GC method was developed and used to simultaneously determine diether lipid and PLFA content in the same GC run. The key features of the method were a slow (1°C/min) temperature ramp through the fatty acid region of the chromatogram followed by a high temperature ramp where the diether lipid eluted. Using this method on both pure bacterial cultures and aquatic sediments, resolution was achieved of the diether lipid and the PLFA, including novel C16 and C18 monounsaturated fatty acids derived from methanotrophs.

Biochemical composition of Nyctiphanes australis and its possible use as an aquaculture feed source: lipids, pigments and fluoride content

Nyctiphanes australis contained, on a dry weight basis, an average of 52% crude protein and 5.0 to 9.5% lipid. The fatty acid profile of N. australis was markedly unsaturated, with a mean total ω3 fatty acid content of 48.6±2.4% of total fatty acids. N. australis contained high levels of the essential long-chain polyunsaturated fatty acids eicosapentaenoic (EPA, 20:5ω3) and docosahexaencic (DHA, 22:6ω3), ranging from 16.6 to 36.5% and 11.1 to 24.8%, respectively. The concentration of total carotenoids ranged from 137 to 302 μg g−1 dry wt, with no significant differences in concentrations found with season or life stage. The carotenoids were comprised of 79.5% astaxanthin and 20.5% canthaxanthin. The lipid and pigment compositions of N. australis suggest that the species could serve as a suitable feed source for cultured salmonids. Like other euphausiids, N. australis contained high levels of fluoride, with a seasonal range between 277 and 3507 μg g−1 dry wt. The high fluoride levels found in N. australis would not detract from its potential as a feed source for salmonids because ingested fluoride is largely absorbed by the skeleton.