A lipid budget for Antarctic krill (Euphausia superba Dana)

Microplankton at five sites off South Georgia in January to February 1991 was dominated by a range of diatoms. The haptophyte Phaeocystis was present in three of the five sites but in low abundance only. Diatoms dominated at a more southerly site near the Antarctic Peninsula in March, whereas dinoflagellates dominated at a site near Deception Island. Multivariate analysis allowed the seven sites to be distinguished on the basis of microplankton species composition. Analysis of thirteen lipid classes present in total lipid extracted from the microplankton also demonstrated substantial differences from site to site. Multivariate analysis showed a different pattern of variation from the species ordination, with the South Georgia sites forming a distinct cluster. Outlier sites identified in the species and lipid ordinations confirmed the association between some taxonomic groups and lipid 'fingerprints'. Fatty acids extracted from total lipid in microplankton at five sites around South Georgia and two sites near the Antarctic Peninsula ranged from 37 to 195 J.Lg1-1, with a ratio of fatty acids in polar lipid: neutral lipid ranging from 4: 1 to 1:2. A further eleven particulate samples analysed from sites around the Antarctic Peninsula had slightly lower fatty acid content with a mean of 50 J.Lg1-1. Fatty acids in polar lipid were rich in (n-3) polyunsaturated fatty acids, chiefly 20:5(n-3). However, 22:6(n-3) could be as abundant as 20:5(n-3) in polar lipid from microplankton less than 20 J.1m, and also in dinoflagellate-rich microplankton. Neutral lipid was dominated by 16:0, 16:1(n-7) and 18:1(n-9) fatty acids and contained only low levels of (n-3) polyunsaturated fatty acids. The data reveal the high nutritional quality of microplankton lipids in the Southern Ocean for filter feeding animals, including krill. Samples of krill from eight sites around South Georgia consisted predominantly of immature animals, and females were entirely absent from samples from two of the eight sites studied. Animal wet mass varied from 0.16-1.72 g (median values of 0.47, 1.15 and 1.46 g for immatures, males and females respectively). Lipid amounts varied from 5-147 mg per animal (median values of 17.8, 21.0 and 73.3 mg for immatures, males and females respectively). Triacylglycerol (TAG) and phosphatidylcholine were the two most abundant lipid classes in all animals. Multivariate analysis of lipid composition indicated significant overlap between sex-maturity classes, although female krill tended to be distinguished from males by higher proportions of TAG and lower proportions of phosphatidylserine plus phosphatidylinositol. Reproductive investment is implicated in the overall variability in lipid content and composition, with females containing high lipid levels as reserves for egg production, whilst males showed apparent lipid deficits resulting from short-term mobilisation of storage material for spermatophore production and attachment. Significant and systematic site-to-site variability in lipid content and composition were evident in the samples and this could not be explained by the sex ratio or animal size. Such variability might have arisen from local patterns of krill distribution but could not be ascribed simply to temporal changes in lipid during the study. Immature Antarctic krill (length 40-45 mm) maintained in an aquarium for up to nine months were fed dense suspensions of cultures of two algal taxa, the haptophyte /sochrysis and the diatom Thalassiosira. Following acclimation to the experimental feeding regime, the animals were transferred to identical containers holding cultures of the same alga already labelled with [14C]bicarbonate. Faecal pellets collected after transfer showed detectable radioactivity after 30 minutes for /sochrysis and 55 minutes for Thalassiosira, providing an estimation of gut throughput time. With both algal cultures, radioactivity in faecal pellets increased over the 4-5 hour collection period. However, whilst faecal pellets derived from Isochrysis showed a rapid initial increase followed by an approach to a plateau value, the radioactivity in Thalassiosira-derived pellets increased steadily. A first-order kinetic model fitted to these data showed a more rapid turnover time for Isochrysis (k = 47 min) than for Thaiassiosira (k = 256 min). The assimilation efficiency based on the ratio of ingested radiolabelled lipid to that egested in faeces was 86% for /sochrysis and 63% for Thalassiosira, whereas corresponding efficiencies calculated from mass lipid budgets were 75% for /sochrysis and 77% for Thalassiosira. Analysis of fatty acid content and composition of total lipid from algae, krill and faecal pellets established that all dietary fatty acids were very efficiently ssimilated although there was a relatively preferential excretion of saturated fatty acids. All the assimilated fatty acids were extensively catabolised with the possible exceptions of saturated fatty acids and 18:4. Evidence was obtained for some biosynthesis of saturated fatty acids from non-lipid dietary precursors and for a limited conversion of 18:3 to 18:4 Collating the data presented in this thesis in a budget indicates that under suitable conditions, Euphausia superba is capable of acquiring the lipid necessary for growth and reproduction over time scales of only a few weeks and certainly within a single summer. Hence, krill appears to be an animal capable of high energy throughput and high reproductive output

Describing additional fluxes to deep sediment traps and water-column decay in a coastal environment

Sediment traps were moored at three stations in Sechelt Inlet, a fjord in southern British Columbia, Canada, for five one-month deployment periods from late January to late June, 1991. On each mooring were traps at three depths; total and constituent fluxes often increased with depth. We present the flux data and describe an analytical model that is based on a set of simultaneous equations for which two unknowns are the decay rate of material representatively caught by two vertically-separated sediment traps and the composition of material causing observed increases in flux with depth. The unknowns are solved in a least-squares sense and the results indicate that 60–71% of organic carbon, 57–62% of nitrogen and 41–48% of biogenic silica were lost from the particulate phase over a 200 m depth interval during the study. The results also suggest that material contributing additional fluxes to deep traps was compositionally similar to material settling from traps above

Hydrostatic Pressure and Temperature Effects on the Membranes of a Seasonally Migrating Marine Copepod

Marine planktonic copepods of the order Calanoida are central to the ecology and productivity of high latitude ecosystems, representing the interface between primary producers and fish. These animals typically undertake a seasonal vertical migration into the deep sea, where they remain dormant for periods of between three and nine months. Descending copepods are subject to low temperatures and increased hydrostatic pressures. Nothing is known about how these organisms adapt their membranes to these environmental stressors. We collected copepods (Calanoides acutus) from the Southern Ocean at depth horizons ranging from surface waters down to 1000 m. Temperature and/or pressure both had significant, additive effects on the overall composition of the membrane phospholipid fatty acids (PLFAs) in C. acutus. The most prominent constituent of the PLFAs, the polyunsaturated fatty acid docosahexanoic acid [DHA – 22:6(n-3)], was affected by a significant interaction between temperature and pressure. This moiety increased with pressure, with the rate of increase being greater at colder temperatures. We suggest that DHA is key to the physiological adaptations of vertically migrating zooplankton, most likely because the biophysical properties of this compound are suited to maintaining membrane order in the cold, high pressure conditions that persist in the deep sea. As copepods cannot synthesise DHA and do not feed during dormancy, sufficient DHA must be accumulated through ingestion before migration is initiated. Climate-driven changes in the timing and abundance of the flagellated microplankton that supply DHA to copepods have major implications for the capacity of these animals to undertake their seasonal life cycle successfully

The role of microbes in the nutrition of detritivorous invertebrates: a stoichiometric analysis

Detritus represents an important pool in the global carbon cycle, providing a food source for detritivorous invertebrates that are conspicuous components of almost all ecosystems. Our knowledge of how these organisms meet their nutritional demands on a diet that is typically comprised of refractory, carbon-rich compounds nevertheless remains incomplete. ‘Trophic upgrading’ of detritus by the attached microbial community (enhancement of zooplankton diet by the inclusion of heterotrophic protozoans) represents a potential source of nutrition for detritivores as both bacteria and their flagellated protistan predators are capable of biosynthesizing essential micronutrients such as polyunsaturated fatty acids (PUFAs). There is however a trade-off because although microbes enhance the substrate in terms of its micronutrient content, the quantity of organic carbon is diminished though metabolic losses as energy passes through the microbial food web. Here, we develop a simple stoichiometric model to examine this trade-off in the nutrition of detritivorous copepods inhabiting the mesopelagic zone of the ocean, focusing on their requirements for carbon and an essential PUFA, docosahexaenoic acid (DHA). Results indicate that feeding on microbes may be a highly favourable strategy for these invertebrates, although the potential for carbon to become limiting when consuming a microbial diet exists because of the inefficiencies of trophic transfer within the microbial food web. Our study highlights the need for improved knowledge at the detritus-microbe-metazoan interface, including interactions between the physiology and ecology of the associated organisms

The effect of high hydrostatic pressure acclimation on acute temperature tolerance and phospholipid fatty acid composition in the shallow-water shrimp Palaemon varians

Extant deep-sea fauna, including hydrothermal vent endemics such as bresiliid shrimp, are descended from shallow-water ancestors. Previous studies have demonstrated the capacity of shallow-water shrimp to acclimate to hydrostatic pressure representative of the vent environment. It has been proposed that this hyperbaric acclimation depends in part on shifts in phospholipid fatty acid composition to maintain biomembrane function. These shifts are also predicted to reduce critical temperature tolerance, potentially limiting the possibility of direct colonisation of the hydrothermal vent environment. Here, we present evidence that acclimation to high hydrostatic pressure (10MPa≈1000m water depth) decreases acute temperature tolerance from 30.2°C to 27.1°C in the shallow-water shrimp Palaemon varians acclimated to 10°C. Statistically significant shifts in phospholipid fatty acid composition occurred during exposure to high hydrostatic pressure, suggesting that homeoviscous modifications support shifts in environmental tolerances during hyperbaric acclimation. Despite the reduction in temperature tolerance, P.varians retains sufficient thermal scope to tolerate the thermal regime in the hydrothermal vent environment, allowing for the possibility of direct deep-sea hydrothermal vent colonisation by shallow-water shrimp

Protozoans as a food source for Antarctic krill, Euphausia superba: complementary insights from stomach content, fatty acids, and stable isotopes

We studied the diet of Antarctic krill, Euphausia superba, at five stations across the southwest Atlantic sector in summer 2003 by analyzing stomach content, fatty acids, and stable isotopes on the same individuals. Our aim was to examine what each method could contribute to our understanding of krill nutrition and whether differences seen in growth rates were linked to their food. All three methods indicated clear regional differences in diet, but small ontogenetic and sex-related differences. Overall, diatoms were the most abundant item in the stomach, but at three of the stations, tintinnids, large dinoflagellates, and other armored flagellates dominated the identifiable biomass. Copepod remains were rare. Fatty acids profiles gave additional information about feeding on weakly silicified diatoms and athecate heterotrophic dinoflagellates, with the latter being the main food source at one of the stations. Two independent indices of carnivory, d15N and the fatty acid ratio 18:1(n-9)/18:1(n-7), were correlated among krill from the same swarm, suggesting consistent differences in diet between individuals. An internal index of trophic position, (i.e., d15Nglutamic acid-d15Nphenylalanine) underlined the importance of heterotrophic food for the nutrition of krill, even in summer. Highest growth rates of krill were found during a diatom bloom and coincided with a mixed diet, large digestive gland, and fast stomach passage. However, even in a nonbloom, flagellate-dominated system, krill were able to sustain medium growth rates when feeding on heterotrophic dinoflagellates. Each method supplied specific information on krill nutrition, and the true picture is only revealed when the various methods are used together

Loss of buoyancy control in the copepod Calanus finmarchicus

A mechanism is demonstrated that could explain large-scale aggregations of lipid-rich copepods in the surface waters of marine environments. Laboratory experiments establish that changes in salinity and temperature induce lipid-mediated buoyancy instability that entrains copepods in surface waters. Reduced hydrostatic pressure associated with forced ascent of copepods at fjordic sills, shelf breaks and seamounts would also reduce the density of the lipid reserves, forcing copepods and particularly those in diapause to the surface. We propose that salinity, temperature and hydrodynamics of the physical environment, in conjunction with the biophysical properties of lipids, explain periodic high abundances of lipid-rich copepods in surface waters

The Optimal Calibration Hypothesis: How Life History Modulates the Brain\u27s Social Pain Network

A growing body of work demonstrates that the brain responds similarly to physical and social injury. Both experiences are associated with activity in the dorsal anterior cingulate cortex (dACC) and anterior insula. This dual functionality of the dACC and anterior insula underscores the evolutionary importance of maintaining interpersonal bonds. Despite the weight that evolution has placed on social injury, the pain response to social rejection varies substantially across individuals. For example, work from our lab demonstrated that the brain\u27s social pain response is moderated by attachment style: anxious-attachment was associated with greater intensity and avoidant-attachment was associated with less intensity in dACC and insula activation. In an attempt to explain these divergent responses in the social pain network, we propose the optimal calibration hypothesis, which posits variation in social rejection in early life history stages shifts the threshold of an individual\u27s social pain network such that the resulting pain sensitivity will be increased by volatile social rejection and reduced by chronic social rejection. Furthermore, the social pain response may be exacerbated when individuals are rejected by others of particular importance to a given life history stage (e.g., potential mates during young adulthood, parents during infancy and childhood)

Blueprints for Green Communities: Climate change visioning and participatory landscape planning for resilient low-carbon communities

Emerging 3D visualization tools and future visioning methods offer new ways to make climate change impacts and potential responses explicit, and accelerate holistic solutions. Previous research at UBC’s Collaborative for Advanced Landscape Planning (CALP) and elsewhere confirms that 4D visioning processes using landscape visualizations of recognizable places under alternative future conditions can improve community engagement and awareness on complex environmental and planning issues (Tress and Tress, 2002; Sheppard and Meitner, 2005; Schroth, 2007). This paper examines a visioning process (Sheppard, 2008) that applies visualization and other landscape planning methods to explore high and low-carbon futures of the affluent, sub-urban hillside community of North Vancouver with climate change, and its surrounding scenic North Shore sub region of Metro Vancouver, BC, Canada