Food and daily food consumption of southern minke whales in the Antarctic

Summary The stomach contents of 273 southern minke whales (Balaenoptera acutorostrata) taken in the region 55°S to the ice-edge and between 105°E and 115°E by a Japanese survey during 1987/88 were examined. The minke whales' dominant feeding ground coincided with a distinctive hydrographic front in the vicinity of the ice-edge at the mouth of Vincennes Bay. Krill (Euphausia superba) were the dominant food species comprising 100% and 94% by weight of stomach contents in the ice-edge and offshore zones, respectively. In the offshore zone, minke whales tend to feed on E. superba rather than Thysanoessa macrura, which is found more frequently than the former in net samples. Total food consumption by minke whales per day was estimated to be 1170 t (22.1 kg/km²) and 596 t (2.0 kg/km²) in the ice-edge and offshore zones, respectively. Feeding activity peaked in the early morning in the ice-edge zone, whereas it occurred irregularly throughout the day in the offshore zone. Two size modes of krill (25–28 mm in body length (1 year-old) and 41–48 mm (3–4 year-old)) dominated the diet. Although the former was numerically more abundant, the latter dominated the diet by weight, suggesting that larger krill are more important food for minke whales. Observed spatial pattern of krill populations in the study region suggests that movement of the subsurface cold water mass tended to carry krill offshore from the ice-edge.The earlier version of this paper was submitted to the 42nd Meeting of the Scientific Committee of International Whaling Commission as SC/42/SHM; 34.     

Vertical distributions and relations of euphausiid populations off Elephant Island,March 1984

Summary Distributional relationships are described for post-larval and larval Euphausia superba and Thysanoessa sp. (probably macrura) and post-larval Euphausia frigida collected in 0–70/80 m and 0–175/200 m depth ranges with a MOCNESS sampler north of Elephant Island (61°S, 55°W) during 17–23 March 1984. Larval E. superba (predominantly calyptopes stage 2 and 3) were rare shallower than 80 m at night. Day catches of post-larval E. suberba were small and night catches were primarily near the top of the thermocline above 50 m depth. Thysanoessa sp. occurred throughout the 0–200 m depth range and was abundant in the upper 80 m both night and day. E. frigida migrated to the upper 80 m at night from deeper day depths. Larval stages of E. superba and bost-larval stages of all three species demonstrated independent and variable vertical distribution patterns both night and day. Changes in E. superba abundance and distributional patterns could to a certain extent be associated with observed environmental changes. An increase in larval and decrease in post-larval E. superba abundances between 0–80 m was associated with an intrusion of cold water at depth. At night, vertically restricted concentrations of post-larval E. superba were associated with shallow mixed layer depths, and a significant vertical separation of developmental stages and size categories was observed only during periods of stratification in the upper 80 m. Fluctuations in the distribution and abundance of Thysanoessa sp. and distribution of E. frigida did not appear to be influenced by physical parameters within the upper 80 m. Within the 0–80 m depth range, the distributions of these two species differed from each other and from E. superba and showed large tow to tow variability that could not be related to physical parameters in the upper water column.     

Variability of Euphausia superba populations near Elephant Island and the South Shetlands: 1981 vs. 1984

Summary March 1981 and 1984 Euphausia superba populations were compared using acoustics and net catches near Elephant Island, the South Shetlands, and in the Bransfield Strait. In 1981, krill tended to form large, thick swarms and in 1984, smaller, more dispersed, shallower patches. March body lengths of juvenile-adult krill were 22–59 mm in 1981 and 13–59 mm in 1984. Near Elephant I. in 1981, krill >45 mm were most numerous; in 1984 sizes <45 mm were dominant. In March 1984, the larger (>45 mm) body-size group was prereproductive and occurred from just west of Elephant I. westward into waters north of the South Shetlands; in 1981 the larger krill were postreproductive and more widely distributed in the Elephant I. area. Overall, netted postlarval krill, 1981 vs. 1984, averaged 73 vs. 48 individuals/m², or 54 vs. 16 g/m²; acoustic biomass estimates were 229 vs. 134–201 g/m². Larvae near Elephant I. averaged >2000/m² in 1981 vs. <1/m² in 1984—compatible with respective March reproductive states. Net-type comparisons revealed short-term (15 min to 6h) variability of a similar scale in both MOCNESS and bongo net catches, but bongo abundances averaged greater. Variation in maturity composition across 1981 swarms, patches, and random transects was like variation among the random 1984 tows; spatial distributions were more heterogeneous in 1984. The March 1984 krill of 20–44 mm (Year-2, mode 34 mm) relate to November 1983 krill of 9–30 mm (mode 21 mm), indicating growth averaging 12 mm during the season. Body-lengths and size-frequency modes of Year-2 and combined Years-3,3+ krill from comparable Feb-Mar data collected since 1968 suggest trends between times when (1) Year-2 krill average small and peak reproduction seems to be late in the season and/or weak (1979, 1982–1984), and (2) Year-2 krill are larger, and reproduction is possibly earlier and more successful (1976, 1980, 1981).     

Larvae of euphausiids off Queen Maud Land

Summary In a March 1981 study of the Lazare Sea, a sector of the Southern Ocean along Queen Maud Land, Euphausia superba and Thysanoessa macrura larvae were abundant in the north and northwest part of the region near the frontal zone between the Weddell Warm Countercurrent (WWC) and Weddell Gyre, 5°W–15°E. Toward the south, E. superba and E. crystallorophias larvae were numerous in the frontal zone between the WWC and the Antarctic Coastal Current. Only T. macrura larvae occurred in the central part of the sea. The age composition of larvae was most advanced in T. macrura, probably due to the drift of larvae from the northwest. Because the ice cover diminishes later in the flow from the Weddell Gyre (northernmost area of the region) than in the south, E. superba larvae were younger in that oceanic subregion than near the shore. T. macrura larvae were sparse near the coast and an onshore-offshore age difference was not pronounced. Both frontal zones correspond to reproductive areas of E. superba and T. macrura. E. crystallorophias spawns only in the southern area.     

Effect of maternal fat reserves on the fatty acid composition of sardine (Sardina pilchardus) oocytes

We compared the fatty acid (FA) composition of the muscle and gonads of female Iberian sardines with hydrated oocytes collected during the 2002/03 spawning season off southern Portugal (November and February) and off western Portugal (February). Sardine condition and total FA concentration in the muscle decreased between the two sampling dates, while the gonadosomatic index was similar between samples. Total monounsaturated FA concentrations in sardine gonads were different for the three samples while saturated and polyunsaturated FA concentrations were similar. Significant linear relations were found between FA concentrations in female muscle and oocytes, including eicosapentaenoic acid (EPA; 20:5n − 3) and arachidonic acid (AA; 20:4n − 6), both being essential for normal larval development. The concentration of docosahexaenoic acid (DHA; 22:6n − 3) in oocytes was independent on muscle concentration, probably resulting from its selective transfer to the oocytes. The EPA/DHA ratio was highly conserved in sardine tissues, while DHA/AA and EPA/AA ratios varied significantly between samples. These results indicate that the FA content of eggs produced by sardines varies throughout the spawning season, egg FA concentrations decreasing as females lose condition, and FA composition also shows spatial variability. Both types of variability may have a significant impact on egg quality, particularly on the amount of reserves available to larvae affecting their resistance to starvation, and the appropriate FA composition required for normal growth.     

Identifying patterns in the diet of mackerel icefish (<Emphasis Type="Italic">Champsocephalus gunnari)</Emphasis> at South Georgia using bootstrapped confidence intervals of a dietary index

Ontogenetic, inter-annual and regional variations in diet were investigated for mackerel icefish, Champsocephalus gunnari, in three successive summer seasons around South Georgia. Stomach contents from 2239 C. gunnari (130–560 mm total length) were examined. A bootstrapping technique was used to calculate confidence intervals for an index of relative importance of prey categories (% IRI_DC). Diet varied significantly between years and age classes but there was little regional difference in diet. In general, diet was dominated by krill, Euphausia superba and by the amphipod Themisto gaudichaudii. Smaller (younger) fish tended to prey on a higher proportion of T. gaudichaudii and small euphausiids such as Thysanoessa sp. and took smaller quantities of E. superba. In a season of poor krill availability (summer of 2003–2004) the proportion of krill in the diet, stomach fullness and fish condition (indicated by length–weight relationships) were significantly lower than in the other summer seasons. A large reduction (>80%) in the estimated annual (2005) biomass of the C. gunnari stock directly followed the season of poor krill availability. This decline was largely because of mortality of 2+ and 3+ fish, which were more krill dependent than 1+ fish. Younger fish appear to have survived, leading to an increase in the estimated population biomass in 2006.     

Fatty acid biomarker ratios—suitable trophic indicators in Antarctic euphausiids?

Fatty-acid biomarkers are frequently used for the identification of trophic relationships among marine zooplankton. We have evaluated the suitability of five fatty-acid ratios [16:0/16:1(n-7), 16:1(n-7)/18:4(n-3), 18:1(n-9)/18:1(n-7), 20:5(n-3)/22:6(n-3), PUFA/SFA] that have been proposed as trophic indicators in the literature. Total lipid content and fatty-acid composition were determined in four Antarctic euphausiid species (Euphausia superba, E. frigida, E. triacantha, Thysanoessa macrura). There is a significant relationship between the lipid content and most of these ratios in the investigated euphausiids. Only the 16:1(n-7)/18:4(n-3) ratio exhibits no clear relationship to total lipids. Further exceptions occur in E. triacantha: the 18:1(n-9)/18:1(n-7) and the 20:5(n-3)/22:6(n-3) ratios are not correlated to the lipid content in this species. There is a weaker correlation between the fatty-acid ratios and the total lipid content in E. superba larvae than in the postlarvae, indicating a stronger dietary influence on the lipids of the younger stages. We conclude that those fatty-acid ratios that strongly depend on an animals total lipid content (particularly PUFA/SFA), are only of limited use as trophic indices, since total lipid content may vary greatly with factors (such as reproductive processes) that are unrelated to specific feeding preferences.     

Lipid and fatty acid yield of nine stationary-phase microalgae: Applications and unusual C<Subscript>24</Subscript>–C<Subscript>28</Subscript> polyunsaturated fatty acids

Nine microalgal species from the classes Bacillariophyceae, Cryptophyceae, Prymnesiophyceae and Dinophyceae were isolated from Australian waters, cultured to stationary phase and analyzed for their lipid and fatty acid composition and yield. Five species (Pavlova pinguis, Heterocapsa niei, Proteomonas sulcata, Navicula jeffreyi and Thalassiosira pseudonana) produced high proportions of triacylglycerol (TAG: 22–57% total lipid). An unidentified Navicula-like diatom (CS-786), despite having a low TAG content, had the highest EPA yield (5.8 mg L⁻¹), due to high biomass and a high relative proportion of EPA. Heterocapsa niei had the highest DHA yield (2.9 mg L⁻¹), due to a high cellular lipid and DHA content (171 pg cell⁻¹ and 13.7 pg cell⁻¹, respectively) despite its relatively low biomass. The desirable PUFA composition and yield of both diatom CS-786 and H. niei make them potential candidates for optimization of biomass and PUFA production for use as live-feeds in aquaculture. In addition, H. niei may have potential as a source of DHA for other uses. Low proportions (< 1.2%) of 24:6(n−3) accompanied by trace proportions of 24:5(n−6) were detected in most strains, while 28:8(n−3) was found in dinoflagellates and also in the prymnesiophyte P. pinguis. All non-diatomaceous species contained 26:7(n−3) in minor quantities. This is the first time these unusual C₂₄ and C₂₆ PUFA have been reported in microalgae and the first report of C₂₈ PUFA in a microalga other than dinoflagellates. Possible biosynthetic reasons why these might occur in stationary phase cultures are considered and the likely dietary transfer of these PUFA to higher aquatic life is discussed.     

n-3 Polyunsaturated fatty acid productivity of the marine microalgaIsochrysis galbana. Growth conditions and phenotypic selection

Two set of isolates were obtained in an isolation/selection programme to select eicosapentaenoic acid (EPA) and/or docosahexaenoic acid (DHA) rich strains ofIsochrysis galbana. EPA content was improved up to an average of 5.3% (d.wt) for the second set of isolates. On the other hand, with the aeration rate, pH and irradiance kept at low levels, the growth rate was slow and EPA synthesis was enhanced, but productivity increased when growth rates were maximum. A model relating steady-state dilution rates in chemostat cultures ofI. galbana to internal average irradiance is proposed. The greatest productivities were obtained between 0.0295 h^–1 and 0.0355 h^–1 with 300 mg m^–3 h^–1 for EPA and 130 mg m^–3 h^–1 for DHA.     

Distribution of salps near the South Shetland Islands during austral summer, 1990–1991 with special reference to krill distribution

Distribution and biomass of salps and Antarctic krill (Euphausia superba) were investigated near the South Shetland Islands during austral summer 1990–1991. Salp biomass ranged between 0 and 556 mgC·m^–3 and was greatest at a station in the Bransfield Strait in late December 1990. Salp biomass was lower than that of E. superba. Two species of salps; Salpa thompsoni and Ihlea racovitzai were found, and the former was dominant numerically. Spatial distribution and generation composition of these two species was different. Spatial distributions of salps and E. superba did not overlap particularly so the January–February period. While E. superba was found mainly in the coastal area which showed high-chlorophyll a values, salps exhibited high biomass in the oceanic area with low chlorophyll a concentrations. Predation by salps on small krill and the competitive removal of food by them, are discussed as potential reasons for the relatively low abundance of E. superba at the stations where salps were present in great numbers.     

Comparisons of morphology and neritic distributions of <Emphasis Type="Italic">Euphausia crystallorophias</Emphasis> and <Emphasis Type="Italic">Euphausia superba</Emphasis> furcilia during autumn and winter west of the Antarctic Peninsula

Euphausia crystallorophias and E. superba larvae often overlap in distribution in Antarctic coastal regions. Here, we describe the morphology and ecology of E. crystallorophias furcilia stages F3–F6, with emphasis on characteristics that distinguish them from E. superba, based on samples collected west of the Antarctic Peninsula during autumn and winter 2001 and 2002. During autumn most E. crystallorophias occurred as F4s (53%) and F5s (35%), while E. superba occurred in all furcilia stages (F1–F6). During winter, F6 was the dominant stage (>67%) for both species. On average, body lengths of E. crystallorophias larval stages were significantly greater than those of E. superba. During autumn, densities of the two species were similar (range: 0.003–11.8 m^–3) at many on-shelf stations, with lower densities during winter. Where both species occurred, >58% of E. crystallorophias furcilia were collected between 50 and 100 m depth, while 82% of E. superba were shallower (25–50 m). Younger stages of E. crystallorophias occurred more frequently (54% of F3s) in water >100 m than older stages (11% of F6s). Thus, many larval E. crystallorophias were vertically segregated from E. superba, thereby reducing grazing competition between the young of these morphologically similar species.     

Ecophysiological studies on citrate-synthase: (I) enzyme regulation of selected crustaceans with regard to temperature adaptation

The characteristics and properties chromatographically purified citrate synthase from the euphausiids Euphausia superba (Antarctica) and Meganyctiphanes norvegica (Scandinavian Kattegat and Mediterranean Sea) and from the isopods Serolis polita (Antarctica) and Idotea baltica (Baltic Sea) were used to elucidate biochemical mechanisms of temperature adaptation. Additionally, maintenance experiments were carried out on the euphausiids to determine mechanisms of short term acclimation. Temperature optima (between 37 and 45°C) were unrelated to genotypic cold adaptation, but the activation energy of the Antarctic krill E. superba (10.9 kJ · mol^-1) was only a quarter of that in other species (41.8–45.1 kJ · mol^-1). The minima of apparent Michaelis constants (total range: 4–20 μmol · 1^-1 oxaloacetate; 7–45 μmol · 1^-1 acetyl-coenzyme A) showed no relation to natural conditions, and no distinct pH optimum occurred at ambient temperatures. In contrast, apparent Michaelis constants and specific enzyme activities were related to maintenance temperatures in M. norvegica, but not in E. superba. The differences between M. norvegica and E. superba can be interpreted as adaptations to the changes in ambient temperature with regard to the respective steno- and eurythermic tolerances of these crustaceans.     

Enhancement of polyunsaturated fatty acid production by cerulenin treatment in polyunsaturated fatty acid-producing bacteria

When docosahexaenoic acid (DHA)-producing Moritella marina strain MP-1 was cultured in the medium containing 0.5 μ g cerulenin ml⁻¹, an inhibitor for fatty acid biosynthesis, the cells grew normally, but the␣content of DHA in the total fatty acids increased from 5.9–19.4%. The DHA yield of M. marina strain MP-1 cells also increased from 4 to 13.7 mg l⁻¹ by cerulenin treatment. The same effect of cerulenin was observed in eicosapentaenoic acid (EPA)-producing Shewanella marinintestina strain IK-1 grown in the medium containing 7.5 μg cerulenin ml⁻¹, and the cerulenin treatment increased the EPA yield from 1.6 to 8 mg l⁻¹. The use of cerulenin is, therefore, advantageous to increase the content of intracellular polyunsaturated fatty acids (PUFA) in particular PUFA-containing phospholipids in bacterial cells.An erratum to this article can be found at .     

Micronekton and macrozooplankton in the open waters near Antarctic ice edge zones (AMERIEZ 1983 and 1986)

Summary Micronekton and macrozooplankton assemblages (0–1000 m) were sampled from the open ocean in the vicinity of marginal ice zones in the southern Scotia and western Weddell Seas using midwater trawls. Small regional differences in species composition were found in the differing hydrographic settings with the Scotia Sea being slightly more diverse. Most species exhibited broad vertical ranges with no distinct pattern of vertical movement. Exceptions were mesopelagic fish and Salpa thompsoni which undertook diel vertical migrations. Biomass was high (2.4–3.1 g DW/m²), comparable to Pacific subarctic waters. Euphausia superba and Salpa tompsoni were the numerical and biomass dominants, representing over 50% of the total numbers and standing stocks. In terms of biomass, euphausiids were the most important group at shallow depths (0–200 m) but were surpassed by salps in the Scotia Sea and mesopelagic fish in the Weddell Sea when all depths down to 1000 m were considered. Pelagic fish biomass (3.3–4.4 g WW/m²) greatly exceeded published estimates for birds (0.025–0.070 g WW/m²), seals (0.068–0.089 g WW/m²) and whales (0.167 to 0.399 g WW/m²), making mesopelagic fish the most prevalent krill predators in the Antarctic oceanic system.     

Differences in growth,total lipid content and fatty acid composition among 60 clones of <Emphasis Type="Italic">Cylindrotheca fusiformis</Emphasis>

Differences between clones of the diatom Cylindrotheca fusiformi were studied with respect to growth rate, total lipid content and fatty acid composition. Sixty clones were isolated and cultivated under batch conditions. All clones were grown under identical conditions (temperature 22±1°C, light intensity 100 μmol photon m⁻² s⁻¹, salinity 28, F/2 medium) and were harvested in the late exponential growth phase for lipid and fatty acid analysis. The results show a wide variation in growth, total lipid content and fatty acid profiles among clones (p<0.05). The major fatty acids in the 60 clones were 14:0 (4.6–9.1%), 16:0 (18.2–32.0%), 16:1n-7 (21.6–33.1%), 20:4n-6 (4.1–13.5%) and 20:5n-3 (6.2–17.2%), with the highest proportion of 20:4n-6 in clone CF13 (13.5%), and the highest proportion of 20:5n-3 in clone CF5 (17.2%). The results support the view that some microalgal fatty acid variation is not restricted to interspecific variation and external factors, but also varies from clone to clone within the same species.     

Natural age-dependent mortality rates of Antarctic krill Euphausia superba Dana in the Indian sector of the Southern Ocean

Data on the size and age composition of Antarctic krill (Euphausia superba Dana) were collected in the Cooperation and Cosmonaut Seas (Indian sector of the Southern Ocean) from 1985 to 1990. The estimation of the age-dependent annual extinction rate of krill [=1-exp(-M)] was obtained using the Zikov and Slepokurov (1982) approach and results were fitted by a parabolic equation. The coefficients of instantaneous natural mortality (M) of E. superba derived with this approach range from 0.52 during the maturation period, to 1.1–2.41 during the first and last years of life.     

Trophic behavior of Euphausia superba Dana in laboratory conditions

Summary Experiments conducted at US Palmer Station, 1980 on antarctic krill, Euphausia superba, attempted 1) to quantify and describe behavioral features of ingestion, food clearance and egestion, and 2) to test the hypotheses that feeding and swarming are mutually exclusive events, and that feeding is a cyclical, diel phenomenon. Ingestion was quantified in a large flow-through aquarium. Food clearance and egestion were estimated visually and fluorometrically in E. superba individually kept in one liter jars. Ingestion was directly proportional to chlorophyll concentration (0.65–11.5 gChl/l) and did not change significantly as a function of krill density (200–9000 krill/m³). Ingestion and egestion did not show significant diel trends or mean day-night differences in a 16 h light-8 h dark cycle. Our results suggested that feeding may occur in nature: at swarm densities, within a wide range of phytoplankton concentrations, and may be sustained throughout the diel cycle. We propose that feeding and swarming are co-occurring events. The theoretical basis at the individual and group levels, and its implications, are briefly discussed.In memory of Mary Alice McWhinnie (1922–1980)This research was supported by the University of Chile, National Science Foundation and Chilean Antarctic Institute     

Alpha-linolenic acid and its conversion to longer chain n−3 fatty acids: Benefits for human health and a role in maintaining tissue n−3 fatty acid levels

There is little doubt regarding the essential nature of alpha-linolenic acid (ALA), yet the capacity of dietary ALA to maintain adequate tissue levels of long chain n−3 fatty acids remains quite controversial. This simple point remains highly debated despite evidence that removal of dietary ALA promotes n−3 fatty acid inadequacy, including that of docosahexaenoic acid (DHA), and that many experiments demonstrate that dietary inclusion of ALA raises n−3 tissue fatty acid content, including DHA. Herein we propose, based upon our previous work and that of others, that ALA is elongated and desaturated in a tissue-dependent manner. One important concept is to recognize that ALA, like many other fatty acids, rapidly undergoes β-oxidation and that the carbons are conserved and reused for synthesis of other products including cholesterol and fatty acids. This process and the differences between utilization of dietary DHA or liver-derived DHA as compared to ALA have led to the dogma that ALA is not a useful fatty acid for maintaining tissue long chain n−3 fatty acids, including DHA. Herein, we propose that indeed dietary ALA is a crucial dietary source of n−3 fatty acids and its dietary inclusion is critical for maintaining tissue long chain n−3 levels.     

Comparison of growth and lipid composition in the green abalone, Haliotis fulgens, provided specific macroalgal diets

Lipid composition of abalone was examined over a one-year interval. A feeding trial was designed to cover a full reproductive cycle in young adult green abalone, Haliotis fulgens, consisting of five diet treatments: the macrophytic algal phaeophyte Egregia menziesii, rhodophyte Chondracanthus canaliculatus, chlorophyte Ulva lobata, a composite of the three algae and a starvation control. The lipid class, fatty acid, sterol and 1-O-alkyl glyceryl ether profiles were determined for foot, hepatopancreas/gonad tissues and larvae. The major fatty acids were 16:0, 18:0, 18:1(n-7)c, 18:1(n-9)c, 20:4(n-6), 20:5(n-3) and 22:5(n-3), as well as 14:0 for abalone fed brown and red algae. 4,8,12-Trimethyltridecanoic acid, derived from algae, was detected for the first time in H. fulgens (hepatopancreas complex, 1.2–13.9%; larvae, 0.5% of total fatty acids). Diacylglyceryl ethers were present in larvae (0.6% of total lipid). The major 1-O-alkyl glycerols were 16:0, 16:1 and 18:0. Additionally, 18:1(n-9) was a major component in hepatopancreas/gonad and larvae. The major sterol was cholesterol (96–100% of total sterols). Highest growth rates were linked to temperature and occurred in abalone fed the phaeophyte E. menziesii (43 μm·day^–1, 56 mg·day^–1 yearly mean), an alga containing the highest levels of C₂₀ polyunsaturated fatty acids and the highest ratio of 20:4(n-6) to 20:5(n-3). This study provides evidence of the influence of diet and temperature on seasonal changes in abalone lipid profiles, where diet is most strongly related to body mass and temperature to shell length. The allocation of lipids to specific tissues in green abalone clarifies their lipid metabolism. These results provide a basis for improving nutrition of abalone in mariculture through formulation of artificial feeds.     

Isolation of quizalofop-resistant mutants of Nannochloropsis oculata (Eustigmatophyceae) with high eicosapentaenoic acid following N-methyl-N-nitrosourea-induced random mutagenesis

Nannochloropsis oculata was subjected to N-methyl-N-nitrosourea-induced mutagenesis under the selection pressure of quizalofop, a known inhibitor of acetyl-CoA carboxylase (ACCase) activity with the objective of generating genetically tractable mutants with altered fatty acid metabolism. Two mutants, QUIZ1 and QUIZ2, with stable resistance to quizalofop were isolated and partially characterized. The growth properties and morphology of the mutants appeared identical with the parent strain. However thermo-tolerance was observed in the mutants. Enhanced resistance to quizalofop suggested the presence of herbicide resistant isoforms of ACCase. In vitro assays for ACCase activity showed that ACCase in the wild strains was much more sensitive to quizalofop than the mutant strains. Gas chromatographic analysis of fatty acids revealed that the mutant strains were rich in polyunsaturated fatty acids (n– 3PUFAs), as well as total fatty acid contents; this was accompanied by a concomitant increase in triacylglycerol (TAG) followed by linoleic acid (18:2), arachidonic acid (20:4 n– 6) and EPA (20:5 n– 3). These results suggest that an increased substrate pool (malonyl-CoA) (due to increased specific activity of ACCase) in the mutant strains in vivo and in vitro may have led to the increased TAG accumulation. Random mutagenesis was shown to be a good tool to manipulate PUFAs and EPA in Nannochloropsis. The strains developed will be useful in understanding fatty acid metabolism using genetic and biochemical approaches and also for their direct use in mariculture.