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Friedrich Buchholz - One of the best experts on this subject based on the ideXlab platform.
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growth and moulting in Northern Krill meganyctiphanes norvegica sars
Advances in Marine Biology, 2010Co-Authors: Friedrich Buchholz, Cornelia BuchholzAbstract:Moulting and growth as a key aspect of the life-history of crustaceans has been reviewed here for Meganyctiphanes norvegica. Moulting is a cyclical process with relatively constrained, uniform phases that have been well documented. The crustacean moult cycle has a large influence on growth-rates, reproduction and metabolism. Moult and growth are under hormonal control with further environmental influences. A pre-requisite for intensive studies is a detailed moult staging system. Here, a further refinement and temporal phasing is presented for M. norvegica. On such a basis, the dynamics of cuticle synthesis and degradation are shown. Moult and reproductive cycles are interlinked and Krill is able to combine growth and reproduction in a way that allows females to achieve similar net growth rates to males. A synchronisation of physiological processes and behaviour related to growth and reproduction enhances environmental success. Moult staging can also be used to assess growth rates in the field. Some further technical approaches are reviewed. Laboratory maintenance and field data are combined to determine growth rates under various environmental conditions. These are related to life-growth assessments from population studies comparing Krill along a latitudinal gradient. Life-cycle and physiological data indicate that Northern Krill are able to cope with both warm and cold environments and have highly adaptable phenotypes. The species may serve as useful indicator of environmental change. Its potential proliferation in new environments may also have implications to regional food webs, given the Krill's high level of growth and productivity and their pivotal trophic role.
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on the timing of moulting processes in reproductively active Northern Krill meganyctiphanes norvegica
Marine Biology, 2006Co-Authors: Cornelia Buchholz, Friedrich Buchholz, Geraint A TarlingAbstract:The interactions between moult phasing, growth and environmental cues in Northern Krill (Meganyctiphanes norvegica) were examined through analysing populations at seasonal, weekly, and daily timescales. The analyses were carried out on resident populations of Krill found in three different neritic locations that experience similar environmental signals (the Clyde Sea, Scotland; the Kattegat, Denmark; Gullmarsfjord, Sweden). Seasonal analyses were carried out on the Clyde Sea population and showed that moulting frequency increased significantly moving from winter to summer. The proportion of moulting females in summer samples was often more than double the proportion of moulting males, suggesting that females had a comparatively shorter intermoult period (IMP). Weekly samples taken from the Kattegat showed a similar pattern. However, although the difference between the proportion of female and male moulters was significant in one week, it was not another, mainly because of the variability in the proportion of female moulters. Such variability in females was equally evident in the daily samples taken at Gullmarsfjord. It suggests that females have a shorter IMP (12.5 days) than males (18.4 days) and are more likely to moult in synchrony. Nevertheless, the daily samples revealed that males are also capable of moult synchronisation, although less frequently than females. Shortened IMPs in females were not a result of the abbreviation of specific moult stages. Accordingly, reproductive activity did not alter the course of the normal moult cycle. There was no significant difference between the total body lengths of males and females indicating that females achieve the same levels of growth despite moulting more frequently and having to provision the energy-rich ovaries. This is in contrast to most other crustaceans where the energy costs of reproduction reduce female growth. The fact that females were less abundant than males, probably by suffering a greater level of mortality, suggests that different behavioural strategies, particularly vertical migration regimes, were adopted by each sex to maximise growth and reproduction.
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experiments on the physiology of southern and Northern Krill euphausia superba and meganyctiphanes norvegica with emphasis on moult and growth a review
Marine and Freshwater Behaviour and Physiology, 2003Co-Authors: Friedrich BuchholzAbstract:Physiological data are needed for life history studies on Krill, and as parameters for input into energy budgets and models. In conjunction with moult and growth data, these may also prove useful for assessing the fishable biomass of Krill. Here, the development of physiological concepts in experimental Krill research is briefly evaluated, with emphasis on the gaps to be filled. Krill growth is very flexible, as well as strongly temperature and nutrition dependent. The polar Antarctic Krill Euphausia superba grows as fast as the boreal species Meganyctiphanes norvegica, at least during the first 2.5 years, and the species are comparable in terms of physiological plasticity. Accordingly, as Krill appear to adjust quickly to specific laboratory conditions, short-term experiments are essential if field conditions are to be reflected as closely as possible. Furthermore, direct comparisons between laboratory experiments and swarming studies in the field are advantageous. For these, M. norvegica is particularly...
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metabolic properties of Northern Krill meganyctiphanes norvegica from different climatic zones ii enzyme characteristics and activities
Marine Biology, 2002Co-Authors: Reinhard Saborowski, Friedrich BuchholzAbstract:Activities and characteristics of two metabolic key enzymes, citrate synthase (CS) and pyruvate kinase (PK), were studied in the Northern Krill, Meganyctiphanes norvegica, with respect to adaptive properties under different thermal conditions. Krill were sampled during late winter/spring and summer from the constantly warm Ligurian Sea (12–13°C below the thermocline), the colder but also comparatively constant Clyde Sea (7–8°C), and the variable Kattegat (2–16°C). Both enzymes showed distinct tissue- and organ-specific activities, which were highest in the pleopods – the principal locomotive organs. The fourth and fifth abdominal segments, however, were used for routine investigation due to lowest variability. Specific activity of CS and PK did not differ between seasons in Krill from the Kattegat or the Clyde Sea. In the Ligurian Sea, in contrast, specific CS activities were significantly lower during summer. Analysis of individual data illustrated a decrease of CS activity with size and an increase of PK activity with size. Taking these allometric effects into account, as emphasized by calculating the ratio between both enzymes, variation of CS and PK activities turned out to be solely dependent on body size, which differed between locations and seasons. Ligurian Krill from the summer, however, were unique in that they showed a lower CS/PK ratio than would be predicted by the scaling effect. Thermal characteristics of each enzyme were similar between locations and seasons. During the winter, in Kattegat and Clyde Sea Krill, K m values (Michaelis–Menten constant) of CS towards acetyl-coenzyme A exhibited an almost constant level over the experimental temperature range of 4–16°C. During summer, however, K m values were lower at 8°C in the Clyde Sea and at 12°C in the Kattegat. In Ligurian Krill from the summer, K m values were consistently lower than those of winter Krill over the entire experimental temperature range. In conclusion, Kattegat and Clyde Sea Krill show only minor adaptations to their respective thermal environments in terms of CS and PK characteristics. Ligurian Krill, in contrast, exhibited decreased specific CS activity during summer, which might be compensated by elevated enzyme–substrate affinity as indicated by lower K m values. Since temperature was constant during both seasons, this effect cannot be explained as a reaction to thermal conditions. Consequently, oligotrophic conditions in the Ligurian Sea during summer may entail a reduction in the somatic performance of Krill, which is reflected by lower CS activity.
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metabolic properties of Northern Krill meganyctiphanes norvegica from different climatic zones i respiration and excretion
Marine Biology, 2002Co-Authors: Reinhard Saborowski, Geraint A Tarling, S Brohl, Friedrich BuchholzAbstract:Adaptive processes linked to overall metabolism were studied in terms of oxygen consumption and ammonia excretion in each of three self-contained Krill populations along a climatic gradient. In the Danish Kattegat, Krill were exposed to temperatures which ranged from 4°C to 16°C between seasons and a vertical temperature gradient of up to 10°C during summer. In the Scottish Clyde Sea, water temperatures varied less between seasons and the vertical temperature gradient in summer was only 3°C. Temperatures in the Ligurian Sea, off Nice, were relatively constant around 12–13°C throughout the year, with a thin surface layer (20–30 m) of warm water developing during summer. The trophic conditions were rich in the Kattegat and, particularly, in the Clyde, but comparatively poor in the Ligurian Sea. Oxygen consumption increased exponentially with increasing experimental temperature, which ranged from 4°C to 16°C. Overall respiration rates were between 19.9 and 89.9 µmol O2 g–1 dry wt h–1. Krill from the Kattegat, the Clyde Sea, and the Ligurian Sea all exhibited approximately the same level of oxygen consumption (30–35 µmol O2 g–1 dry wt h–1) when incubated at the ambient temperatures found in their respective environments (9°C, 5°C, and 12°C). This indicates that Krill adjust their overall metabolic rates to the prevailing thermal conditions. The exception to this were the respiration rates of Ligurian Krill from winter/spring, which were about twice as high as the rates from summer Krill despite the fact that the thermal conditions were the same. This effect appears to result from enhanced somatic activity during a short period of increased food availability and reproduction. Accordingly, Krill appears to be capable of adapting to both changing thermal and trophic conditions, especially when nutrition is a limiting factor in physiological processes.
Geraint A Tarling - One of the best experts on this subject based on the ideXlab platform.
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effects of chronic crude oil exposure on early developmental stages of the Northern Krill meganyctiphanes norvegica
Journal of Toxicology and Environmental Health, 2017Co-Authors: Maj Arnberg, Elisa Ravagnan, Leon Moodley, Evgenia Dunaevskaya, Sreerekha Ramanand, Anna Ingvarsdottir, Marianne Nilsen, Stig Westerlund, Steinar Sanni, Geraint A TarlingAbstract:ABSTRACTRising oil and gas activities in Northern high latitudes have led to an increased risk of petroleum pollution in these ecosystems. Further, seasonal high UV radiation at high latitudes may elevate photo-enhanced toxicity of petroleum pollution to marine organisms. Zooplanktons are a key ecological component of Northern ecosystems; therefore, it is important to assess their sensitivity to potential pollutants of oil and gas activity. As ontogenetic development may be particularly sensitive, the aim of this study was to examine the impact of chronic exposure to oil water dispersion (OWD) on development and feeding of early life stages of the Northern Krill, Meganyctiphanes norvegica. In a range of experiments, embryonic, nonfeeding, and feeding larval stages were exposed to concentrations of between 0.01 and 0.1 mg/L of oil or photo-modified oil for 19 and 21 d. No significant effects on egg respiration, hatching success, development, length and larval survival were observed from these treatments. S...
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an introduction to the biology of Northern Krill meganyctiphanes norvegica sars
Advances in Marine Biology, 2010Co-Authors: Geraint A Tarling, Natalie S Ensor, Torsten Fregin, W P Goodallcopestake, Peter T FretwellAbstract:This chapter provides a background to research on Northern Krill biology, starting with a description of its morphology and identifying features, and the historical path to its eventual position as a single-species genus. There is a lack of any euphausiid fossil material, so phylogenetic analysis has relied on comparative morphology and ontogeny and, more recently, genetic methods. Although details differ, the consensus of these approaches is that Meganyctiphanes is most closely related to the genus Thysanoessa. The light organs (or photophores) are well developed in Northern Krill and the control of luminescence in these organs is described. A consideration of the distribution of the species shows that it principally occupies shelf and slope waters of both the western and eastern coasts of the North Atlantic, with a southern limit at the boundary with sub-tropical waters (plus parts of the Mediterranean) and a Northern limit at the boundary with Arctic water masses. Recent evidence of a northward expansion of these distributional limits is considered further. There have been a variety of techniques used to sample and survey Northern Krill populations for a variety of purposes, which this chapter collates and assesses in terms of their effectiveness. Northern Krill play an important ecological role, both as a contributor to the carbon pump through the transport of faecal material to the deeper layers, and as a key prey item for groundfish, squid, baleen whales, and seabirds. The commercial exploitation of Northern Krill has been slow to emerge since its potential was considered by Mauchline [Mauchline, J (1980). The biology of mysids and euphausiids. Adv. Mar. Biol. 18, 1-681]. However, new uses for products derived from Krill are currently being found, which may lead to a new wave of exploitation.
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population dynamics of Northern Krill meganyctiphanes norvegica sars
Advances in Marine Biology, 2010Co-Authors: Geraint A TarlingAbstract:This chapter reviews the short- and long-term changes in the size and age composition of Northern Krill (Meganyctiphanes norvegica) populations and the environmental processes influencing those changes. It examines how populations of this species are affected by rates of reproductive output and mortality, and the effects of development, immigration and dispersion on population structure. This review also takes account of the many behavioural features that directly or indirectly influence M. norvegica population dynamics, such as swarming behaviour, diel vertical migration and diverse feeding strategies. What becomes evident is that M. norvegica shows a wide variability in population size-structure over the species extensive distributional range. Nevertheless, there are limits to this variability, as a result of the common life-cycle pattern.
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improving acoustic estimates of Krill experience from repeat sampling of Northern Krill meganyctiphanes norvegica in gullmarsfjord sweden
Ices Journal of Marine Science, 2007Co-Authors: Inigo Everson, Geraint A Tarling, Bo BergstromAbstract:A series of eight replicated acoustic surveys, four by day and four by night, was undertaken in Gullmarsfjord on the Swedish west coast during two 24-h periods on 8 and 10 September 2003, using a calibrated echosounder operating at 120 and 38 kHz. The difference in signal strength (Sv) was used to distinguish Northern Krill (Meganyctiphanes norvegica) from other acoustic scatterers. The approach is concluded to be very effective, but it can be improved greatly by applying the following series of simple extensions to current protocols: first, set a very low threshold on both frequencies to minimize sampling bias; second, undertake tests to confirm that the data extracted from each acoustic frequency apply to the same scatterers; third, ensure that the range of Sv is not greater than the TSrange at either frequency; and finally, when abundance estimation is the primary aim, arrange for sampling at the time of day and using the acoustic frequency that together provide the least variance.
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on the timing of moulting processes in reproductively active Northern Krill meganyctiphanes norvegica
Marine Biology, 2006Co-Authors: Cornelia Buchholz, Friedrich Buchholz, Geraint A TarlingAbstract:The interactions between moult phasing, growth and environmental cues in Northern Krill (Meganyctiphanes norvegica) were examined through analysing populations at seasonal, weekly, and daily timescales. The analyses were carried out on resident populations of Krill found in three different neritic locations that experience similar environmental signals (the Clyde Sea, Scotland; the Kattegat, Denmark; Gullmarsfjord, Sweden). Seasonal analyses were carried out on the Clyde Sea population and showed that moulting frequency increased significantly moving from winter to summer. The proportion of moulting females in summer samples was often more than double the proportion of moulting males, suggesting that females had a comparatively shorter intermoult period (IMP). Weekly samples taken from the Kattegat showed a similar pattern. However, although the difference between the proportion of female and male moulters was significant in one week, it was not another, mainly because of the variability in the proportion of female moulters. Such variability in females was equally evident in the daily samples taken at Gullmarsfjord. It suggests that females have a shorter IMP (12.5 days) than males (18.4 days) and are more likely to moult in synchrony. Nevertheless, the daily samples revealed that males are also capable of moult synchronisation, although less frequently than females. Shortened IMPs in females were not a result of the abbreviation of specific moult stages. Accordingly, reproductive activity did not alter the course of the normal moult cycle. There was no significant difference between the total body lengths of males and females indicating that females achieve the same levels of growth despite moulting more frequently and having to provision the energy-rich ovaries. This is in contrast to most other crustaceans where the energy costs of reproduction reduce female growth. The fact that females were less abundant than males, probably by suffering a greater level of mortality, suggests that different behavioural strategies, particularly vertical migration regimes, were adopted by each sex to maximise growth and reproduction.
Reinhard Saborowski - One of the best experts on this subject based on the ideXlab platform.
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related antipodes a comparative study on digestive endopeptidases from Northern Krill and antarctic Krill euphausiacea
Polar Biology, 2012Co-Authors: Reinhard SaborowskiAbstract:The Antarctic Krill, Euphausia superba, and the Northern Krill, Meganyctiphanes norvegica, are closely related species but occupy significantly different trophic and climatic environments. E. superba holds a key position as a phytoplankton grazer in the Southern Ocean. The omnivorous M. norvegica is an important member of plankton communities in the Northeast Atlantic. Both species expressed high proteolytic activities which were dominated by serine proteinases. In the stomachs of Antarctic Krill, activities of total proteinase, trypsin, and chymotrypsin were significantly higher than in Northern Krill. In the midgut glands, however, total proteinase and trypsin activities were similar in both species, but chymotrypsin activity was significantly higher in Antarctic Krill. Moreover, Antarctic Krill expressed four trypsin isoforms while only one isoform appeared in Northern Krill. Chymotrypsin was present in either species as one single isoform. Antarctic Krill adapted to the low and patchy distribution of food by elevated enzyme activities and the expression of trypsin isoforms with slightly different catalytic properties. Presumably, these enzymes facilitate in concerted action the efficient utilization of proteins from phytoplankton, the major food. Northern Krill, in contrast, seems not to be equipped to face food limitation. It expresses a “simple” or “basic” set of digestive enzymes for utilizing abundant and easily digestible prey.
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food utilization of two pelagic crustaceans in the greenland sea meganyctiphanes norvegica euphausiacea and hymenodora glacialis decapoda caridea
Marine Ecology Progress Series, 2010Co-Authors: Tobias Kreibich, Wilhelm Hagen, Reinhard SaborowskiAbstract:Large pelagic crustaceans from Greenland Sea waters, the Northern Krill Meganyc- tiphanes norvegica (Euphausiacea) and the decapod shrimp Hymenodora glacialis (Caridea), were captured in depths down to 1500 m and studied with respect to their physiological food utilization abilities. Both species showed distinct differences in the amount of total lipids (TLs), lipid class and fatty acid (FA) compositions as well as proteolytic enzyme activities. In M. norvegica, the overall amount of TLs and storage lipids was much lower than in H. glacialis, and triacylglycerols formed the major lipid fraction with a mean of 48% TLs. Major FAs comprised the trophic markers 20:1(n-9) and 22:1(n-11), indicating the ingestion of calanid copepods. Additionally, the FAs 22:6(n-3), 18:1(n-9) and 16:0 prevailed. In H. glacialis, TLs (mean = 44% dry mass) were about twice as high as in Krill, with wax esters comprising up to 89% TLs. H. glacialis seems to accumulate these lipids as energy reserves to survive periods of food limitation. Moreover, high lipid levels, particularly wax esters, also help to maintain neutral buoyancy. The major FA in H. glacialis was 18:1(n-9); other dominant FAs were 20:1(n-9) and 22:1(n-11), typical of calanid copepods, as well as the diatom trophic marker 16:1(n-7). Both species showed omnivorous feeding behaviour with a strong tendency towards carni- vory. Total proteolytic activities in midgut gland tissue were higher in M. norvegica than in H. glacialis. In M. norvegica, proteinases were dominated by serine proteinases, whereas cysteine proteinases formed the major group in H. glacialis. High proteolytic activity in M. norvegica indicates a high digestive potential for proteins and efficient utilization of prey. The presence of different pro- teinase classes in both species may be due to different group-specific enzyme expression patterns between euphausiids and caridean decapods. Both species follow highly deviating life strategies, as reflected by their specific lipid and enzymatic characteristics.
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physiology and metabolism of Northern Krill meganyctiphanes norvegica sars
Advances in Marine Biology, 2010Co-Authors: John I Spicer, Reinhard SaborowskiAbstract:Advances in our understanding of the physiology and metabolism of Northern Krill, Meganyctiphanes norvegica have been sporadic but significant. Despite problems with keeping M. norvegica in good condition in the laboratory, those who have tried, and succeeded, have contributed to a better knowledge of Krill biology and challenged our understanding of some basic biological processes. Most recent work has been concentrated in the fields of digestive physiology, lipid biochemistry, respiration and anaerobiosis, metabolic properties, and pollutants. M. norvegica is capable of digesting an opportunistic, omnivorous diet, showing some digestive enzyme polymorphism and high levels of enzyme activity, the latter varying with season. It also seems capable of digesting cellulose and hemicelluloses, for example, laminarin. The biochemical composition of Krill is relatively well known with some recent extensive work focusing on the previously little studied lipid and fatty acid composition, particularly with reference to reproduction, overwintering energy storage and as a nutrition marker. A high aerobic metabolism (but poor anaerobic capacity) is characteristic of M. norvegica, and how this is affected by temperature, low O(2), and season has attracted some attention, particularly in the context of diel vertical migration (DVM) across pronounced pycnoclines. Despite determining high metabolic turnover rates and a high physiological plasticity for this species, we know little of the regulative potential of metabolites, particularly their modulative effect on enzyme activity. Certainly a modest ability to maintain aerobic metabolism when encountering hypoxia, and little or no ability to osmoregulate in hyposaline conditions, does not prevent DVM in adults of this species. The ability to maintain aerobic metabolism develops early in ontogeny at about furcilia III (i.e. concurrent with first DVM behaviour). The respiratory pigment of M. norvegica, haemocyanin, has a low O(2) affinity and high temperature sensitivity (although temperature has the opposite effect on O(2) binding than found for nearly every other haemocyanin). Also surprising is the apparent use of haemocyanin as an energy source/store. While recent work has focused on physiological effects, the ecophysiological effects of transuric elements and trace metals, the effects of pollution generally are widely understudied.
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tissue specific distribution of pyruvate kinase isoforms improve the physiological plasticity of Northern Krill meganyctiphanes norvegica
Journal of Experimental Marine Biology and Ecology, 2006Co-Authors: M Salomon, Reinhard SaborowskiAbstract:Abstract The Northern Krill, Meganyctiphanes norvegica (Crustacea, Euphausiacea) is widely distributed in the Northern and northeastern parts of the Atlantic Ocean where it faces rapid variations in water temperatures and food. We studied the physiological potential of Krill to compensate for environmentally induced metabolic changes. Two isoforms of the glycolytic key enzyme pyruvate kinase (PKI and PKII, EC 2.7.1.40) were partly purified from M. norvegica by anion exchange chromatography. Specific activities and catalytic properties of each isoform were determined in whole body extracts as well as in selected organs and tissues of males and females. Both PK-isoenzymes differed slightly in their temperature profiles, their activation energy and their molecular weights. PKI showed a high affinity for the substrate PEP and was not affected by fructose-1.6-bisphosphate (FBP). In contrast, PKII showed low affinity for PEP but was strongly activated by FBP, up to 40-fold. The specific PK-activity of whole organisms was lower in females (44.9 ± 4.8 U·g ww − 1 ) than in males (61.3 ± 7.7 U·g ww − 1 ). In females PK II represented 20% of the total PK-activity while it was only 10% in males. Highest PK activities were present in the hearts, the eyes, pleopods and in the thoracopods. In the stomachs and the midgut glands PK activities were low. Almost all organs contained PKI and PKII. However, PKI prevailed in the abdomens, the pleopods, the thoracopods, and in the thoracic muscles. PKII dominated in the eyes, the midgut glands and in the ovaries. Experiments showed that the tissue concentrations of FBP increased with food uptake and temperature. The expression of two PK-isoforms with different kinetic properties and the mediation of substrate affinity by FPB is a powerful tool to immediately regulate glycolytic energy flows in different organs. The Krill is capable of adjusting energy consumption to changes in nutritional conditions as well as variations of environmental temperatures.
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metabolic properties of Northern Krill meganyctiphanes norvegica from different climatic zones ii enzyme characteristics and activities
Marine Biology, 2002Co-Authors: Reinhard Saborowski, Friedrich BuchholzAbstract:Activities and characteristics of two metabolic key enzymes, citrate synthase (CS) and pyruvate kinase (PK), were studied in the Northern Krill, Meganyctiphanes norvegica, with respect to adaptive properties under different thermal conditions. Krill were sampled during late winter/spring and summer from the constantly warm Ligurian Sea (12–13°C below the thermocline), the colder but also comparatively constant Clyde Sea (7–8°C), and the variable Kattegat (2–16°C). Both enzymes showed distinct tissue- and organ-specific activities, which were highest in the pleopods – the principal locomotive organs. The fourth and fifth abdominal segments, however, were used for routine investigation due to lowest variability. Specific activity of CS and PK did not differ between seasons in Krill from the Kattegat or the Clyde Sea. In the Ligurian Sea, in contrast, specific CS activities were significantly lower during summer. Analysis of individual data illustrated a decrease of CS activity with size and an increase of PK activity with size. Taking these allometric effects into account, as emphasized by calculating the ratio between both enzymes, variation of CS and PK activities turned out to be solely dependent on body size, which differed between locations and seasons. Ligurian Krill from the summer, however, were unique in that they showed a lower CS/PK ratio than would be predicted by the scaling effect. Thermal characteristics of each enzyme were similar between locations and seasons. During the winter, in Kattegat and Clyde Sea Krill, K m values (Michaelis–Menten constant) of CS towards acetyl-coenzyme A exhibited an almost constant level over the experimental temperature range of 4–16°C. During summer, however, K m values were lower at 8°C in the Clyde Sea and at 12°C in the Kattegat. In Ligurian Krill from the summer, K m values were consistently lower than those of winter Krill over the entire experimental temperature range. In conclusion, Kattegat and Clyde Sea Krill show only minor adaptations to their respective thermal environments in terms of CS and PK characteristics. Ligurian Krill, in contrast, exhibited decreased specific CS activity during summer, which might be compensated by elevated enzyme–substrate affinity as indicated by lower K m values. Since temperature was constant during both seasons, this effect cannot be explained as a reaction to thermal conditions. Consequently, oligotrophic conditions in the Ligurian Sea during summer may entail a reduction in the somatic performance of Krill, which is reflected by lower CS activity.
Janine Cuzinroudy - One of the best experts on this subject based on the ideXlab platform.
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reproduction in Northern Krill meganyctiphanes norvegica sars
Advances in Marine Biology, 2010Co-Authors: Janine CuzinroudyAbstract:This review presents the current state of knowledge with regard to the reproductive biology of Northern Krill (Meganyctiphanes norvegica). Reproduction is limited to a distinct period of the year. First development of the ovary occurs at the onset of the season, when the stock of primary oocytes issued from the germinal zone starts to accumulate glycoproteic yolk. Previtellogenesis continues throughout the entire reproductive season, but oosorption (the retrieval by the ovary of the yolk constituents from the growing oocytes) may occur in unfavourable conditions and represents an important metabolic process for sustaining females during such periods. Oosorption also occurs at the onset of the resting season. It has been established that individual females may perform several cycles of reproduction each year. Each reproductive cycle spans two moult cycles, one in which lipid yolk is accumulated (vitellogenesis) and another when spawning occurs. The time of spawning does not coincide with the moult (ecdysis), but with the onset of moult preparation (C-D0 moult stages). The complete egg-batch is spawned well before the moult. Storage lipids are accumulated preferentially in the ovary with distinctly high levels of ω-3 polyunsaturated fatty acids in the polar lipid fraction as well as phosphatidylcholine, a key component in the development of the embryo. There is no difference concerning lipid storage between resting females, males and juvenile Krill. Beside the ovary, the fat body is an important organ involved in the metabolism and storage of the glycoproteins and lipids that will be transformed into the lipoglycoproteins of the yolk platelets in the ovary. M. norvegica produce large egg batches with the number of mature oocytes in one batch being proportional to the size of the female, with a mean number of 1000-1200 eggs per batch. The number of reproductive cycles per year is a function of the trophic conditions, with the first reproductive cycle being triggered by the first phytoplankton bloom. Other reproductive features reflect specific adaptations of Krill to a pelagic life, like swarming and vertical migration behaviour. M. norvegica segregate at night for moulting and mating or spawning, while swimming constantly during their diel vertical migration (DVM). Key questions concerning Krill reproduction remain, particularly in identifying the cues that switch Krill in and out reproductive development, or between egg-building and oosorption. New molecular tools are now available to tackle such questions.
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life cycle strategies of Northern Krill meganyctiphanes norvegica for regulating growth moult and reproductive activity in various environments the case of fjordic populations
Ices Journal of Marine Science, 2004Co-Authors: Janine Cuzinroudy, Geraint A Tarling, J O StrombergAbstract:Adaptive strategies of two fjord populations of Northern Krill (Meganyctiphanes norvegica Sars) were studied and compared with other populations from different climatic and oceanic conditions. The Gullmarsfjord (West Sweden) and the Clyde Sea (West Scotland) resident populations followed the same basic pattern of development as the Kattegat (between Denmark and Sweden) and the Ligurian Sea (Northwest Mediterranean) populations, but the fjord Krill reached a comparatively larger body size during their second year of life. The positive relationship between body size and fecundity means that fjord populations are potentially more productive than those of the open sea. High rates of moulting and spawning activity were limited to the spring and summer despite the fact that trophic conditions still seemed favourable in early autumn. We show here that, in autumn, the adult moult cycle became longer and growth stopped, large 2-year-old Krill disappeared from the population and ovarian development was arrested. Resources already accumulated ill the oocytes (glycoproteic and lipid yolk) were recovered by oosorption and ovaries regressed for a winter rest. Autumn trophic conditions were still favourable in both sites, especially in terms of copepod abundance. However, the phytoplankton community changed from a dominance of diatoms in early season to dinoflagellates in late summer. We suggest that these changes triggered the autumn arrest of Krill production.
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synchronization in the molting and spawning activity of Northern Krill meganyctiphanes norvegica and its effect on recruitment
Limnology and Oceanography, 2003Co-Authors: Geraint A Tarling, Janine CuzinroudyAbstract:The molting, spawning, and recruitment of Northern Krill (Meganyctiphanes norvegica ) were analyzed over an annual cycle (1999‐2000) in the Clyde Sea (west coast of Scotland). Results supported the hypothesis of a functional relationship between egg production and molt development for the duration of the reproductive season (March to August), with one reproductive cycle being made up of two molt cycles. Females remained in reproductive condition throughout the reproductive season, and the timing of their spawning and molting was synchronized at the population level throughout this period. A semiempirical model predicted that the Krill population produced an egg pulse every 20 to 26 d (depending on temperature), and three cohorts were evident in net samples taken later in the year. The likely date on which the first cohort was spawned was around 26 d after the main phytoplankton bloom, suggesting that the bloom triggered egg development in all adult females. Such a synchronized spawning period was observed directly in adult females 26 d after a bloom in March 2000. A total of three cohorts over the 6-month reproductive season is less than the maximum of seven that would be possible if spawning occurred at a periodicity of between 20 and 26 d, suggesting that larval recruitment was not always successful. Analysis showed that successful recruitment was only achieved when chlorophyll a levels were adequate during both the period of egg maturation in the ovary and the subsequent development of larvae, especially the furcilia stages. The reproductive cycles of euphausiids are known to be adapted to local conditions. The length and timing of the spawning season varies interspecifically, from the apparently continuous breeding of Euphausia hanseniin the subtropical Benguela upwelling system to the seasonally distinct breeding episodes of Euphausia superba in the Antarctic (Siegel 2000). Intraspecific variation is also evident in widely distributed species, such as Northern Krill ( Meganyctiphanes norvegica), that have short reproductive seasons in Mediterranean waters (e.g., the Ligurian Sea) but longer reproductive seasons in temperate boreal regions (e.g., the Clyde Sea and the Kattegat). A common pattern throughout the range of this species is the coincidence of reproductive scheduling with periods of optimal trophic conditions (Cuzin-Roudy and Buchholz 1999). The abundance of food items in boreal North Atlantic areas is generally high from early spring to late summer, facilitating a reproductive season that lasts from March to October. In the Mediterranean, the large blooms of
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variation of lipid classes among organs of the Northern Krill meganyctiphanes norvegica with respect to reproduction
Comparative Biochemistry and Physiology A-molecular & Integrative Physiology, 2001Co-Authors: Eric Albessard, Patrick Mayzaud, Janine CuzinroudyAbstract:Lipid content and class in the Northern Krill Meganyctiphanes norvegica (digestive gland, stomach, gonad, fat body, abdomen) was investigated and correlated with sex and reproductive stage. Ready to spawn females, have high lipid content in ovaries, while in males and spent females, the major site of lipid deposits was the digestive gland, followed by the fat body. These differences among spawning and spent females are indicative of strong interactions between the ovary and digestive gland and the ovary and fat body during vitellogenesis. Triacylglycerols (TAG) were the major neutral lipid class with high levels in the digestive gland. The major phospholipid was phosphatidylcholine (PC) particularly in the muscular tissue of the abdomen. Phosphatidyl-ethanolamine (PE) and -serine-inositol (PS-PI), were present at intermediate levels. Reproductive males were depleted in TAG and diacylglycerols (DAG) in the digestive gland, gonad and fat body, and had 4 times lower cholesterol in the gonad than ready to spawn females. Furthermore, ready to spawn females had in the ovary higher amounts of TAG, DAG and phospholipids (PC, PE, PS-PI) than spent females. Linear relationships between lipid content and main lipid class (TAG, PC, PE, PS-PI) in different fractions of males and ready to spawn females showed that: (1). TAG was stored for both sexes in all cephalothorax fractions with highest values in the digestive gland and ovary fluid; (2). PC was accumulated for both sexes in the fat body and the gonad with a higher slope for females, with the highest values in the ovary fluid and in the abdomen of males and that (3). PS-PI was stored only in the ovary and abdomen of mature females. These results are discussed in terms of the strategy developed by Meganyctiphanes norvegica to allocate lipids to the next generation for optimised embryogenesis.
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seasonal reproduction multiple spawning and fecundity in Northern Krill meganyctiphanes norvegica and antarctic Krill euphausia superba
Canadian Journal of Fisheries and Aquatic Sciences, 2000Co-Authors: Janine CuzinroudyAbstract:Both Northern Krill, Meganyctiphanes norvegica, and Antarctic Krill, Euphausia superba, release eggs seasonally in multiple spawning events. Fecundity estimates were determined based on counts of m...
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variation of lipid classes among organs of the Northern Krill meganyctiphanes norvegica with respect to reproduction
Comparative Biochemistry and Physiology A-molecular & Integrative Physiology, 2001Co-Authors: Eric Albessard, Patrick Mayzaud, Janine CuzinroudyAbstract:Lipid content and class in the Northern Krill Meganyctiphanes norvegica (digestive gland, stomach, gonad, fat body, abdomen) was investigated and correlated with sex and reproductive stage. Ready to spawn females, have high lipid content in ovaries, while in males and spent females, the major site of lipid deposits was the digestive gland, followed by the fat body. These differences among spawning and spent females are indicative of strong interactions between the ovary and digestive gland and the ovary and fat body during vitellogenesis. Triacylglycerols (TAG) were the major neutral lipid class with high levels in the digestive gland. The major phospholipid was phosphatidylcholine (PC) particularly in the muscular tissue of the abdomen. Phosphatidyl-ethanolamine (PE) and -serine-inositol (PS-PI), were present at intermediate levels. Reproductive males were depleted in TAG and diacylglycerols (DAG) in the digestive gland, gonad and fat body, and had 4 times lower cholesterol in the gonad than ready to spawn females. Furthermore, ready to spawn females had in the ovary higher amounts of TAG, DAG and phospholipids (PC, PE, PS-PI) than spent females. Linear relationships between lipid content and main lipid class (TAG, PC, PE, PS-PI) in different fractions of males and ready to spawn females showed that: (1). TAG was stored for both sexes in all cephalothorax fractions with highest values in the digestive gland and ovary fluid; (2). PC was accumulated for both sexes in the fat body and the gonad with a higher slope for females, with the highest values in the ovary fluid and in the abdomen of males and that (3). PS-PI was stored only in the ovary and abdomen of mature females. These results are discussed in terms of the strategy developed by Meganyctiphanes norvegica to allocate lipids to the next generation for optimised embryogenesis.
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on the food of Northern Krill meganyctiphanes norvegica in relation to its vertical distribution
Marine Ecology Progress Series, 2001Co-Authors: Sandra Lass, Geraint A Tarling, Patti Virtue, J B L Matthews, Patrick Mayzaud, Friedrich BuchholzAbstract:The feeding behaviour of Northern Krill (Meganyctiphanes norvegica) was studied in populations from the Clyde Sea and the Kattegat during summer and winter. The food spectrum in the stomachs was analysed using traditional taxonomic methods and biochemical techniques. The vertical migration behaviour of Krill was monitored through a 30 h series of net samples, whilst the trophic environment was characterised through accompanying quantitative analyses on the depth distribution and biomass of copepods and phytoplankton. Krill was found to be more carnivorous in the Kattegat than in the Clyde Sea, which correlated with the higher ratio of copepod to phytoplankton biomass found in the Kattegat compared with the Clyde Sea. High levels of fatty alcohols and other lipid markers in the stomach contents of Kattegat Krill were also indicative of a carnivorous diet. Other food sources included detritus, terrestrial material and other euphausiids, underlining the opportunistic nature of Northern Krill in its choice of prey items. Analyses of stomach and intestinal fullness over a diel cycle showed significant variations with time in the Clyde Sea but not in the Kattegat. However, a diel cycle in the rate of ingestion was evident at both locations when comparing the copepod mandibles in the stomachs to the distribution of copepods in the environment. The fact that deep-living Calanus was not a major prey item suggested that there was little feeding activity during the daytime, when the Krill occupied the deeper layers. Instead, the majority of mandibles were from species that were dominant in the upper layers, e.g. the genera Temora and Pseudocalanus. The fact that Krill caught in the daytime contained the same relative composition of mandibles in the stomach as those caught at night is probably explained by a cessation in daytime feeding activity and retention of the mandibles from the night before. It is proposed that Krill in the Clyde Sea area and the Kattegat show a diel rhythm in feeding activity that is believed to be an adaptive response to minimising predation risk.
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studies on metabolic properties in the Northern Krill meganyctiphanes norvegica crustacea euphausiacea influence of nutrition and season on pyruvate kinase
Comparative Biochemistry and Physiology A-molecular & Integrative Physiology, 2000Co-Authors: M Salomon, Patrick Mayzaud, Friedrich BuchholzAbstract:Abstract The specific activity and the kinetic properties of partly purified pyruvate kinase (PK) (EC 2.7.1.40) from the Northern Krill, Meganyctiphanes norvegica , were investigated in relation to varying food resources. In order to evaluate the effect of starvation on the total energy metabolism, the respiration rates of fed and unfed Krill were determined. The FPLC–elution profile of PK displayed two distinct peaks — PK I and II. The first isoform represented 80% of the total PK activity in the organism, and 20% was contributed by the second isoform. PK I was inhibited by ATP but was not influenced by fructose–1,6–bisphosphate (FBP). In contrast, PK II showed ATP inhibition and up to 2.5-fold increased activity by addition of 17 μmol·l −1 FBP. The Michaelis–Menten constants of both isoforms were 2–10-fold higher for ADP than for phosphoenolpyruvate (PEP). Alanine showed no regulatory effect on PK I and II. In specimens starved for 7 days oxygen consumption decreased by 20%. Neither the feeding experiments nor the animals captured in the field during low and high productive seasons indicate that PK properties of M. norvegica are modified in relation to food supply. Accordingly, alternative mechanisms are involved in the depression of the metabolic rate in terms of oxygen consumption.
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use of fatty acids as dietary indicators in Northern Krill meganyctiphanes norvegica from northeastern atlantic kattegat and mediterranean waters
Canadian Journal of Fisheries and Aquatic Sciences, 2000Co-Authors: Patti Virtue, Patrick Mayzaud, Eric Albessard, Peter D NicholsAbstract:Nous avons compare les fractions trialcylglycerol (TG) et lipides polaires (LP) des acides gras chez des specimens de Meganyctiphanes norvegica preleves en mer de Clyde, dans l'Atlantique, au Kattegat dans la fosse Alkor, et dans la mer Ligurienne en Mediterranee. Nous avons examine les biotransformations possibles des acides gras dans la chaine trophique en etudiant du zooplancton melange et de la matiere fecale de Krill de la mer Ligurienne et du Kattegat. La population ligurienne se distinguait de celles du Kattegat et de la mer de Clyde par les profils des acides gras. tant TG que LP. Les populations du Kattegat et de la mer de Clyde se distinguaient l'une de l'autre seulement par leurs profils des acides gras TG. Le Krill capture en hiver a toutes les stations presentait des niveaux significativement superieurs des acides gras 20:1 et 22:1 dans la fraction TG (9-17%) que le Krill echantillonne en ete (1-10%). Ces acides gras en particulier indiquent des apports d'alimentation carnivore, car on les retrouve en fortes concentrations chez les copepodes qui sont la proie principale de M. norvegica. Les niveaux de 22:6(n-3) etaient nettement plus eleves que ceux de 20:5(n-3) chez le Krill ligurien, ce qui, en combinaison avec d'autres acides gras qui sont des marqueurs specifiques, indique une predominance des dinoflagelles et d'autres especes autres que des diatomees dans leur alimentation. La presence d'acides gras TG chez le Krill du Kattegat et de la mer de Clyde indique la predominance des diatomees dans l'alimentation de ces crustaces.
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an optimisation model of the diel vertical migration of Northern Krill meganyctiphanes norvegica in the clyde sea and the kattegat
Canadian Journal of Fisheries and Aquatic Sciences, 2000Co-Authors: Geraint A Tarling, Reinhard Saborowski, Friedrich Buchholz, J B L Matthews, Michael T Burrows, Alain Bedo, Patrick MayzaudAbstract:Nous avons elabore un modele d'optimisation pour examiner les effets du risque de predation et des conditions environnementales sur la migration verticale nycthemerale du Krill nordique (Meganyctiphanes norvegica) adulte. Les predictions du modele ont ete comparees a deux endroits presentant des conditions environnementales tres differentes, la mer de Clyde et le Kattegat. Le modele a ete construit a partir d'une combinaison de fonctions parametrisees et de donnees empiriques de terrain obtenues dans des conditions estivales. Les matrices des parametres ont ete etablies de facon a couvrir l'ensemble de la colonne d'eau sur une periode de 24 h. La premiere matrice contenait des valeurs correspondant au « gain energetique net » qui integraient les donnees empiriques sur la respiration dependante de la temperature, l'abondance des copepodes et du phytoplancton et un modele de reaction fonctionnelle pour le taux d'alimentation. La deuxieme matrice exprimait le risque de rencontrer un predateur visuellement generalise (poisson) en fonction du niveau d'eclairement. La procedure d'optimisation a formule un cheminement dans la profondeur et dans le temps de facon que le gain energetique soit egal a la quantite necessaire pour la croissance, la production d'oeufs et la mue, tandis que le risque de predation etait minimise. Le modele a predit la migration verticale nycthemerale en mer de Clyde et dans le Kattegat. Des analyses de sensibilite ont montre que le patron de migration predit etait essentiellement regi par l'alimentation et le risque de predation, les effets de la temperature sur les couts metaboliques n'ayant qu'un effet mineur.