Low Algal Biomass Research Articles

Nitrogen Sources and Sinks Within the Middle Rio Grande, New Mexico1

Abstract: Relationships between discharge, land use, and nitrogen sources and sinks were developed using 5 years of synoptic sampling along a 300 km reach of the Rio Grande in central New Mexico. Average river discharge was higher during 2001 and 2005 “wet years” (15 m3/s) than during the drought years of 2002‐04 “dry years” (8.9 m3/s), but there were no differences in nitrogen loading from wastewater treatment plants (WWTPs) which were the largest and most consistent source of nitrogen to the river (1,330 kg/day). Average total dissolved nitrogen (TDN) concentrations remained elevated for 180 km downstream of the Albuquerque WWTP averaging 1.2 mg/l in wet years and 0.52 mg/l in dry years. Possible explanations for the constant elevated TDN concentrations downstream of the major point source include reduced nitrogen retention capacity, minimal contact with riparian or channel vegetation, large suspended sediment loads, and low algal biomass. Somewhat surprisingly, agricultural return flows had lower average nitrogen concentrations than river water originally diverted to agriculture in both wet (0.81 mg/l) and dry years (0.19 mg/l), indicating that the agricultural system is a sink for nitrogen. Lower average nitrogen concentrations in the river during the dry years can be explained by the input of agricultural returns which comprise the majority of river flow in dry years.

Linking ice structure and microscale variability of algal biomass in Arctic first-year sea ice using an in situ photographic technique

Microscale photographs were taken of the ice bottom to examine linkages of algal chlorophyll a (chl a) biomass distribution with bottom ice features in thick Arctic first-year sea ice during a spring field program which took place from May 5 to 21, 2003. The photographic technique developed in this paper has resulted in the first in situ observations of microscale variability in bottom ice algae distribution in Arctic first-year sea ice in relation to ice morphology. Observations of brine channel diameter (1.65–2.68 mm) and number density (5.33–10.35 per 100 cm2) showed that the number of these channels at the bottom of thick first-year sea ice may be greater than previously measured on extracted ice samples. A variogram analysis showed that over areas of low chl a biomass (≤20.7 mg chl a m−2), patchiness in bottom ice chl a biomass was at the scale of brine layer spacing and small brine channels (∼1–3 mm). Over areas of high chl a biomass (≥34.6 mg chl a m−2), patchiness in biomass was related to the spacing of larger brine channels on the ice bottom (∼10–26 mm). Brine layers and channels are thought to provide microscale maxima of light, nutrient replenishment and space availability which would explain the small scale patchiness over areas of low algal biomass. However, ice melt and erosion near brine channels may play a more important role in areas with high algal biomass and low snow cover.

The effect of irradiance, vertical mixing and temperature on spring phytoplankton dynamics under climate change: long-term observations and model analysis

Spring algal development in deep temperate lakes is thought to be strongly influenced by surface irradiance, vertical mixing and temperature, all of which are expected to be altered by climate change. Based on long-term data from Lake Constance, we investigated the individual and combined effects of these variables on algal dynamics using descriptive statistics, multiple regression models and a process-oriented dynamic simulation model. The latter considered edible and less-edible algae and was forced by observed or anticipated irradiance, temperature and vertical mixing intensity. Unexpectedly, irradiance often dominated algal net growth rather than vertical mixing for the following reason: algal dynamics depended on algal net losses from the euphotic layer to larger depth due to vertical mixing. These losses strongly depended on the vertical algal gradient which, in turn, was determined by the mixing intensity during the previous days, thereby introducing a memory effect. This observation implied that during intense mixing that had already reduced the vertical algal gradient, net losses due to mixing were small. Consequently, even in deep Lake Constance, the reduction in primary production due to low light was often more influential than the net losses due to mixing. In the regression model, the dynamics of small, fast-growing algae was best explained by vertical mixing intensity and global irradiance, whereas those of larger algae were best explained by their biomass 1 week earlier. The simulation model additionally revealed that even in late winter grazing may represent an important loss factor during calm periods when losses due to mixing are small. The importance of losses by mixing and grazing changed rapidly as it depended on the variable mixing intensity. Higher temperature, lower global irradiance and enhanced mixing generated lower algal biomass and primary production in the dynamic simulation model. This suggests that potential consequences of climate change may partly counteract each other.

Differential Response of Algae on Small Streambed Substrates to Floods

Abstract The effect of floods and base flow on temporal variation in algal biomass on small smooth streambed stones and creviced sand-cases of the caddisfly (Insecta: Trichoptera) Gumaga nigricula was examined in Big Sulphur Creek in coastal Northern California. Replicates of stones and cases were sampled 34 times over a 14 mo period that included nine floods. Stones had ∼2× the algal biomass of cases, based on chlorophyll a concentration. The lower algal biomass on caddisfly cases is consistent with this species' burrowing behavior, which reduces algal biomass by abrasion and light limitation. Algal biomass on stones was reduced by floods and generally increased in the absence of floods. In contrast, neither floods nor extended base flow affected the pattern of algal biomass on caddisfly cases, and biomass on caddisfly cases often exceeded that on stones following floods. Streambed substrates with different textures may provide different degrees of disturbance-protection for benthic microalgae, and rough...

Hydrological seasonality and benthic algal biomass in a Neotropical floodplain river

Our study evaluated spatiotemporal variation of physicochemical parameters and benthic and sestonic algal biomass in littoral areas of the main channel and floodplain lakes of the Cinaruco River, a lowland tributary of the Orinoco River in Venezuela. The Cinaruco is characterized by a highly predictable annual flood pulse, high transparency, and extremely low conductivity and suspended sediment load. During 2002 and 2003, 10 sites in the main channel and floodplain lagoons were sampled on 12 occasions. Correspondence analysis based on water physicochemical variables and algal biomass showed that ˜80% of the variation in the multivariate space among sites and sampling dates was explained by 2 axes. During the high-water periods, river and lagoon sites showed high similarity in water variables and algal biomass. Conductivity, SiO3, and chlorophyll a concentrations (both benthic and sestonic) were low during the high-water phase. On the other hand, water variables and algal biomass differed between river and lagoon sites during the low-water period. The absence of flow in lagoons and consistently low algal biomass (sestonic and benthic) in river sites were the most important features of the spatial variability between main channel and lagoon sites during low-water phases. Benthic chlorophyll a was highly uniform at small spatial scales and significantly heterogeneous at large spatial scales. The annual flood regime of the Cinaruco, which drives the concentrations of dissolved materials and affects material interchanges between aquatic and terrestrial systems, also appears to be responsible for creating strong patterns of seasonal and spatial variation in benthic algal crops.

Divergent composition of algal-bacterial biofilms developing under various external factors

The influence of external factors other than nutrients on biofilm development and composition was studied with a combination of optical (Confocal Laser Scanning Microscopy, PAM fluorometry) and chemical methods (EPS extraction, HPLC, TOC determination). The development of algal-bacterial biofilms was followed from bare surfaces to mature biofilms in two water reservoirs on Dutch filtration dunes. Biofilms developed under the influence of grazing, light limitation or undisturbed by either of these two factors. Biofilms appeared similar at the beginning of the colonization period at the three sites and laser microscopy observations revealed the predominance of bacteria and capsular EPS (extracellular polymeric substances) in young biofilms. After 3 weeks development, the biofilms had a higher number of taxa; undisturbed biofilms presented the highest biomass, the longest developmental period and showed a significant correlation between organic carbon, chlorophyll and EPS production, indicating a close coupling between autotrophic carbon production and EPS. In light-limited biofilms, this coupling was weaker (although the organic carbon content was similar to that of the undisturbed biofilms) and a lower algal biomass was reached. Light-limited biofilms were mostly composed of diatoms, which are more efficient in low irradiances than green microalgae. Biofilms grazed by the snail Potamopyrgus antipodarum presented the lowest biomass level, but the highest proportion of EPS. Grazing seemed to favour the predominance of EPS-rich algae, as well as firmly attached diatoms. Although filamentous cyanobacteria were found in mature biofilms at the three locations, they were more abundant in the grazed biofilms. The differences in carbon uptake with respect to its allocation indicated that external factors influencing biofilm development affect the cycling and transport of carbon in biofilms and hence influence the effect of biofilm metabolism on the overlying water quality.

Community resistance and change to nutrient enrichment and fish manipulation in a vegetated lake littoral

Summary1. High biomass of macrophytes is considered important in the maintenance of a clear‐water state in shallow eutrophic lakes. Therefore, rehabilitation and protection of aquatic vegetation is crucial to the management of shallow lakes.2. We conducted field mesocosm experiments in 1998 and 1999 to study community responses in the plant‐dominated littoral zone of a lake to nutrient enrichment at different fish densities. We aimed to find the threshold fish biomass for the different nutrient enrichment levels below which large herbivorous zooplankton escapes control by fish. The experiments took place in the littoral of Lake Vesijärvi in southern Finland and were part of a series of parallel studies carried out jointly at six sites across Europe.3. In 1998, when macrophyte growth was poor, a clear‐water state with low phytoplankton biomass occurred only in unenriched mesocosms without fish or with low fish biomass (4 g fresh mass m−2). Both nutrient enrichment and high fish biomass (20 g fresh mass m−2) provoked a turbid water state with high planktonic and periphytic algal biomass. The zooplankton community was dominated by rotifers and failed to control the biomass of algae in nutrient enriched mesocosms. The littoral community thus had low buffer capacity against nutrient enrichment.4. In 1999, macrophytes, especially free‐floating Lemna trisulca L., grew well and the zooplankton community was dominated by filter‐feeding cladocerans. The buffer capacity of the littoral community against nutrient enrichment was high; a clear‐water state with low phytoplankton biomass prevailed even under the highest nutrient enrichment. High grazing rates by cladocerans, together with reduced light penetration into the water caused by L. trisulca, were apparently the main mechanisms behind the low algal biomass.5. Effects of fish manipulations were less pronounced than effects of nutrient enrichment. In 1999, clearance rates of cladocerans were similar in fish‐free and low‐fish treatments but decreased in the high‐fish treatment. This suggests that the threshold fish biomass was between the low‐ and high‐fish treatments. In 1998, such a threshold was found only between fish‐free and low‐fish treatments.6. The pronounced difference in the observed responses to nutrient enrichment and fish additions in two successive years suggests that under similar nutrient conditions and fish feeding pressure either clear or turbid water may result depending on the initial community structure and on weather.

Long-term dynamics of phytoplankton assemblages: Microcystis-domination in Lake Taihu, a large shallow lake in China

Long-term phytoplankton assemblages in a large shallow Chinese lake, Lake Taihu, were presented using the monthly monitoring data from October 1991 to December 1999. Earlier research results (1960, 1981 and 1988) were applied to discuss the different trophic stages of the lake. The species composition in the lake was more closely related to eutrophication level than to lake-size, shallowness, or turbidity. Each summer, a single peak of phytoplankton biovolume appeared in Meiliang Bay. The results of principal components analysis showed a distinct temporal shift in species composition between summer and winter. A clear spatial difference in phytoplankton occurred between Meiliang Bay and the lake centre. Wind speed and direction affected the horizontal distribution of phytoplankton, especially Microcystis, in the lake. Temperature, underwater light climate, nutrients and grazing by zooplankton and by fish were discussed to explain the overwhelming dominance of Microcystis. Four nutrient-phytoplankton stages were identified in the lake: an oligo-mesotrophic stage with low algal biomass until 1981, a eutrophic situation with blooms of Microcystis during 1988-1995, hypertrophic conditions with the dominance of Planctonema and total phosphorus up to 200 mg m -3 from 1996 to 1997 and the restoration period after 1997. The wax and wane of the phytoplankton assemblages were mainly controlled by temperature, wind and turbidity while long-term biomass dynamics were influenced by the level of nutrients.

Seasonal and Spatial Variation in Algal Composition and Biomass on the Central Florida Gulf Coast Shelf

Information on primary producers is fundamental to the understanding of communities. Little is known about the primary producers of marine communities at intermediate depths on the Florida Gulf Coast shelf. The diversity and biomass of algae and seagrass were studied seasonally at three offshore sites (12- to 18-m depth) and one nearshore site (6-m depth) on the central Florida Gulf Coast shelf. Thirty-eight species of attached and drift macroalgae and one drifting seagrass, Thalassia testudinum, were found. The deepest collection site was the most productive in terms of standing biomass and had much more flora on limestone rubble than on sand. All other sites had relatively low floral biomass. Algal diversity varied considerably with season at 6- and 12-m depths, whereas a more stable diversity was observed at 18m. Plant and algal communities in the Gulf of Mexico vary greatly between sites of different depths even when in close proximity. Intermediate depths contained lower algal biomass with more variable species composition over time than the deeper offshore sites.

Assessing the influence of water and substratum quality on benthic macroinvertebrate communities in a metal‐polluted stream: an experimental approach

SUMMARY 1. Field and laboratory experiments were conducted to assess the relative influence of water quality and substratum quality on benthic macroinvertebrate communities in the Animas River, a metal‐polluted stream in south‐western Colorado (U.S.A.).2. A community‐level in situ toxicity test measured direct effects of Animas River water on benthic invertebrates collected from a reference stream (Elk Creek). The effects of metal‐contaminated biofilm were examined by comparing macroinvertebrate colonisation of clean and contaminated substrata placed in Elk Creek. A feeding experiment with the mayfly Baetis tricaudatus Dodds (Ephemeroptera: Baetidae) examined metal bioaccumulation and effects of metal‐contaminated biofilm on growth and survival.3. Animas River water was acutely toxic to most taxa, with greatest effects observed on mayflies (Heptageniidae, Ephemerellidae) and stoneflies (Taeniopterygidae and Capniidae).4. Although Animas River biofilm was characterised by high concentrations of metals and low algal biomass, most taxa colonised substratum from the reference stream and the Animas River equally. The exceptions were Ephemerellidae, Taeniopterygidae and Simuliidae, which were less abundant on Animas River substratum. Mayflies grazing Animas River biofilm accumulated significantly more metals and showed reduced growth compared with organisms feeding on Elk Creek biofilm.5. Results of our experiments demonstrated that effects of heavy metals on benthic community structure in the Animas River were complex, and that responses to metals in water and contaminated substratum were species‐specific. Predicting recovery of benthic communities following remediation requires an understanding of these species‐specific responses.

Assessing trophic state of an endorheic tropical lake: the algal growth potential and limiting nutrients

Lake Zirahuen is one of Mexico's most beautiful lakes. It is apparently endorheic. The highly transparent waters with very low algal biomass characterize an oligotrophic condition. Nevertheless, the external nutrient load and the potential for internal nutrient loads in an anoxic hypolimnion predict eutrophy. To determine if the low algal biomass in the lake is due to nutrient control or to inhibition by pollution from copper goods manufacturing in the watershed, we undertook algal bioassays of the lake and inflowing stream waters. The algal growth potential of the stream water was high but was zero for the lake waters. Nutrient additions showed nitrogen and phosphorus colimitation for the lake and phosphorus limitation for the stream waters. The good growth found with added nutrients eliminates copper inhibition as the cause of the low in-lake algal growth. These data suggest that the lake is not endorheic but has significant subsurface flushing of the inflowing nutrients, and also includes internal controls precluding nutrients mobilization into the food web.

Some aspects of photosynthetic characteristics in a set of perennial irrigation reservoirs located in five river basins in Sri Lanka

Phytoplankton primary productivity of eleven irrigation reservoirs located in five river basins in Sri Lanka was determined on a single occasion together with light climate and nutrient concentrations. Although area-based gross primary productivity (1.43–11.65 g O2 m−2 d−1) falls within the range already established for tropical water bodies, net daily rate was negative in three water bodies. Light-saturated optimum rates were found in water bodies, with relatively high algal biomass, but photosynthetic efficiency or specific rates were higher in water bodies with low algal biomass, indicating nutrient limitation or physiological adaptation of phytoplankton. Concentrations of micronutrients and algal biomass in the reservoirs are largely altered by high flushing rate resulting from irrigation release. Underwater light climate and nutrient availability control the rate of photosynthesis and subsequent areabased primary production to a great extent. However, morpho-edephic index or euphotic algal biomass in the most productive stratum of the water column is not a good predictor of photosynthetic capacity or daily rate of primary production of these shallow tropical irrigation reservoirs.

Relation of environmental factors to density of epilithic lotic bacteria in 2 ecoregions

AbstractAlthough heterotrophic bacteria are important components of stream ecosystems, little is known about the factors that contribute to their abundance. We used data from 69 streams to examine both the direct and indirect effects of algal biomass (chlorophyll a), dissolved organic C (DOC), NO3−, soluble reactive P (SRP), and NH4+ on bacterial density. All potential relationships were simultaneously evaluated using path analysis. Streams in 2 ecoregions (unglaciated and glaciated) were used to determine if important factors varied between ecoregions. The results indicated that algal biomass was the best predictor of bacterial density in both ecoregions. Furthermore, inorganic nutrients appeared to mainly affect bacteria indirectly through their influence on algal biomass. However, a quantitative relationship between algae and bacteria was not observed when algal biomass was <5 μg chlorophyll a/cm2. The lack of relationship between algae and bacteria at low algal biomass may help to explain why some stu...

Multiple dynamics in a single predator-prey system: experimental effects of food quality.

Recent work with the freshwater zooplankton Daphnia has suggested that the quality of its algal prey can have a significant effect on its demographic rates and life-history patterns. Predator-prey theory linking food quantity and food quality predicts that a single system should be able to display two distinct patterns of population dynamics. One pattern is predicted to have high herbivore and low algal biomass dynamics (high HBD), whereas the other is predicted to have low herbivore and high algal biomass dynamics (low HBD). Despite these predictions and the stoichiometric evidence that many phytoplankton communities may have poor access to food of quality, there have been few tests of whether a dynamic predator-prey system can display both of these distinct patterns. Here we report, to the authors' knowledge, the first evidence for two dynamical patterns, as predicted by theory, in a single predator-prey system. We show that the high HBD is a result of food quantity effects and that the low HBD is a result of food quality effects, which are maintained by phosphorus limitation in the predator. These results provide an important link between the known effects of nutrient limitation in herbivores and the significance of prey quality in predator-prey population dynamics in natural zooplankton communities.

International study on Artemia LXIII. Field study of the Artemia urmiana (Günther, 1890) population in Lake Urmiah, Iran

Lake Urmiah is a large (total surface 4750–6100 km2 in recent times) thalassohaline hypersaline lake (150–180 g l−1 in the period 1994–1996), located in northwestern Iran. It is the habitat of the endemic Artemia urmiana. Over the period July 1994–January 1996 a sampling campaign was organized: 36 fixed sampling stations, distributed over the entire lake's area, were sampled weekly to determine water temperature, salinity and transparency. At each occasion a filter net was dragged over a distance of 400 m in the superficial water layer to assess the density and composition of the Artemia population. A more limited sampling campaign focused on the annual fluctuations in chlorophyll concentration and on the reproductive behaviour of the brine shrimp population. Several stages of brine shrimp survived during winter months (water temperature 3°C) at low densities. Compared to available data for the Great Salt Lake, USA, Lake Urmiah shows a low algal biomass and overall low Artemia density. The increasing grazing pressure of the developing brine shrimp population in spring seems to prevent the phytoplankton from reaching high blooming concentrations, and oviparity is the dominant reproductive mode throughout the reproductive season.

Algal biomass in a disturbed Atlantic river: water quality relationships and environmental implications

Benthic algal biomass was determined at 38 sites along the Oria, a river with intense human activity on its watershed. Water temperature, total suspended solids and nutrient concentration affected algal biomass in different ways. Lower values of algal biomass [(chlorophyll- a concentration and ash-free dry weight (AFDW)] were found in the headwaters and forested tributaries, but also at sites receiving high deposition of solids (due to the outflow from paper mills and quarries). Higher values of algal biomass (both chlorophyll- a and AFDW) were common both in the main stretch of the river and in some tributaries receiving urban sewage outflows. Averages and ranges of temperature and dissolved oxygen concentration were compared for two continuously monitored stations. One of them (forested, nutrient-poor) had low algal biomass, while the second (open, nutrient-rich) showed high chlorophyll- a concentration. Accumulation of algal biomass had environmental implications both in water quality and in the fish diversity of the Oria. Diel variations of dissolved oxygen were much higher (and reached hypoxia) at the site with higher biomass accumulation. The abundance of a fish community (dominated by cyprinids) more tolerant to hypoxia at that site can partly be attributed to the influence of algal biomass accumulation.

Application of sequence-specific labeled 16S rRNA gene oligonucleotide probes for genetic profiling of cyanobacterial abundance and diversity by array hybridization.

DNA sequence information for the small-subunit rRNA gene (16S rDNA) obtained from cyanobacterial cultures was used to investigate the presence of cyanobacteria and their abundance in natural habitats. Eight planktonic communities developing in lakes characterized by relatively low algal biomass (mesotrophic) and in lakes with correspondingly high biomass (eutrophic) were selected for the study. The organismal compositions of the water samples were analyzed genetically, using multiplex sequence-specific labeling of oligonucleotide probes targeted to 16S rDNA and subsequent hybridization of the labeled probes to their respective complements spotted onto a solid support (DNA array). Ten probes were established to determine the relative abundances of the discernible cyanobacteria encountered in the selected lakes. The probes were generally specific for their targets, as determined through analyses of clone cultures. Reproducible abundance profiles were established for the lakes investigated in the subsequent analyses of natural cyanobacterial communities. The results from the genetic analyses were then compared with information obtained from standard hydrobiological and hydrochemical analyses. Qualitatively, there were relatively good correlations among the groups of organisms (Nostoc, Microcystis, and Planktothrix species) found in the different lakes. The levels of correlation were lower for the quantitative data. This may, however, be due to differences in sample processing technique. The conclusions from these comparisons are that the genetic abundance profiles may provide a foundation for separating and quantifying genetically distinct groups of cyanobacteria in their natural habitats.

The functional and aggregative responses of a herbivore: underlying mechanisms and the spatial implications for plant depletion

Summary 1. The functional and aggregative responses of dark‐bellied brent geese Branta bernicla bernicla feeding on the green algae Enteromorpha intestinalis and Ulva lactuca are described. 2. Bite rate showed maxima at both high and low algal biomass, although the functional response in terms of biomass intake rate was linear (type‐1). The differences in the shapes of these responses can be explained by the fact that bite size declines with decreasing algal biomass. 3. There was little interference between the geese; the rate of aggression was only weakly related to goose density, and time spent feeding decreased only slightly with increasing density. 4. Geese fed on all parts of the algal bed, showing weak, but significant aggregation in patches of higher algal biomass in both October and November. 5. The observed pattern of aggregation was weaker than that predicted by the ideal free distribution with a low value of interference. 6. Simulation models were used to explore four possible behavioural factors leading to this deviation from predictions: cost of travel between patches, constraints on the perception of patch quality, disturbance and short‐term resource guarding. It is concluded that resource‐guarding is likely to be the most important contributory factor.

Effect of primary producers on the heterotrophic metabolism of a stream biofilm

1. ,The influence of benthic algae on heterotrophic metabolism in a forested Mediterranean stream was investigated. Bacterial density and ectoenzymatic activities, as well as algal biomass (chlorophyll‐a) and metabolism (the rate of 14C incorporation), were measured during colonization over 60 days of artificial substrata (clay tiles) under light and dark conditions.2. ,Chlorophyll‐a and the rate of 14C incorporation were significantly higher in light‐grown than in dark‐grown biofilms. Bacterial density and ectoenzymatic activity (especially β‐glucosidase) were also significantly higher in light‐grown biofilms.3. ,Regressions of chlorophyll‐a and 14C incorporation values on the ectoenzymatic activities were significant. The slopes of regression lines obtained for dark‐grown biofilms were significantly higher than those obtained for light ‐grown biofilms.4. ,The differences in the slope (of the regression lines) between dark and light‐grown biofilms suggest that the response of the heterotrophs is faster in biofilms with low algal biomass accrual and slows down when algal biomass is increased.5. ,It is concluded that algal accumulation in the epilithic biofilm influences the use of organic matter by the heterotrophic community by increasing the amount of organic substrate available for bacteria.

Fatty acid content of Antarctic krill Euphausia superba at South Georgia related to regional populations and variations in diet

The fatty acid content of Antarctic krill Euphausia superba from South Georgia was investigated during January and February 1996, a period of relatively low algal biomass. Cluster analysis of the fatty acid data revealed 3 regionally distinct groups of krill. Group A consisted primarily of sub-adults (median length 42 mm) and was characterised by high proportions of 14:0, 16:0 and 18:1(n-9) fatty acids. Group B comprised mainly juveniles and a small proportion of adults (median length 33 mm) and had a fatty acid profile similar to that of Group A. The largest group, Group C (8 of 14 stations, mostly to the east of the survey area), was almost exclusively juveniles plus a small number of sub-adults (median length 29 mm) and had unusually high percentages of polyunsaturated fatty acids [PUFA; 18:4(n-3), 20:5(n-3) and 22:6(n-3)]. Krill from Group C had the lowest total fatty acid concentrations (150 to 722 mg kg-1). These krill were surviving on the lowest algal biomass in the region and had probably resorted to carnivory on PUFA rich copepods. The pattern of fatty acids in krill from Groups A and B resembled that of krill collected from a diatom bloom in the Bellingshausen Sea, but the concentrations were generally lower. The well fed krill from the Bellingshausen Sea showed small variations in fatty acid content associated with sex and maturity, but the South Georgia results indicated that diet can have a greater impact on fatty acid content than sex and maturity stages. Fatty acid profiles were indicative of food regimes that were so distinct that the krill probably originated from spatially independent groups.