Ammonium cycling by Antarctic zooplankton in winter

Huntley, Mark E.; Nordhausen, Walter

doi:10.1007/bf00349454

Cited by 23 publications

(22 citation statements)

References 42 publications

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“…For acclimated krill, rates measured during feeding were significantly higher than those in filtered seawater (t-test, P Ͻ 0.05). For a 60-mg dry mass krill, the maximum daily excretion equates to a daily loss of 1.9% of their nitrogen content, assuming that nitrogen content is 10% of dry mass (Ikeda and Bruce 1986;Ishii et al 1987;Ikeda and Kirkwood 1989;Huntley and Nordhausen 1995).…”

Section: Resultsmentioning

confidence: 99%

“…Total rations (i.e., the percentage of body carbon ingested per day) were calculated by summing the ingestion rates of individual food items and by assuming that carbon contents of both krill and copepods were 45% of their dry mass (Schnack 1985;Ikeda and Kirkwood 1989;Huntley and Nordhausen 1995). Carbon contents of diatom taxa were calculated from Eppley et al (1970).…”

Section: Methodsmentioning

confidence: 99%

“…However, the South Georgia system supports an exceptionally high metazooplankton biomass, often at least half of which is krill (Ward et al 1995;Pakhomov et al 1997b;Atkinson et al 1999). Because of contrasting suggestions over the large-scale importance of ammonium regeneration by krill (Olson 1980;Owens et al 1991;Huntley and Nordhausen 1995;Priddle et al 1997), this topic warrants further appraisal. We have therefore made some simple calculations using our mean and maximum values to set some limits to estimates of their ammonium production rate (Fig.…”

Section: Excretion In Relation To Feeding-mentioning

confidence: 99%

“…In the western area (moderate krill biomass, high primary production), krill appear to contribute little, but they could be important in the eastern area, with high krill and lower primary production. It is well known that krill swarms could be important localized sources of regenerated nitrogen (Hirche 1983;Johnson et al 1984;Huntley and Nordhausen 1995). So far, however, suggestions about their importance over wider scales have been contradictory, largely because of uncertainties over their natural rates of excretion (Olson 1980;Huntley and Nordhausen 1995;Priddle et al 1997).…”

Section: Excretion In Relation To Feeding-mentioning

confidence: 99%

“…cretion rates of freshly caught zooplankton reflect genuine rates or are the result of the stress of capture (Båmstedt and Tande 1985;Huntley and Nordhausen 1995). Given these uncertainties and the wide range of krill excretion rates in the literature, further assessments are needed to quantify this part of their energy budget.…”

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confidence: 99%

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Ammonium excretion by Antarctic krill Euphausia superba at South Georgia

Atkinson

Whitehouse

2000

Limnology & Oceanography

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Excretion by Antarctic krill Euphausia superba (hereafter ''krill'') is measured typically in small containers of filtered seawater for 12-24 h, which may cause a reduction of swimming, feeding, and metabolism. If the maximum published excretion rates are realistic, krill would be a major source of regenerated nitrogen in the South Georgia area because of their high biomass there. Because literature values are variable, depending on season, feeding history and the experimental set-up, our aim was to measure both a mean and an upper value of krill excretion rate at South Georgia. Experiments were on juvenile krill during October-November 1997 and January 1998. Freshly caught animals excreted 1.6-2.8 nmol ammonium mg Ϫ1 dry mass h Ϫ1; within the fivefold range of summer literature values for equivalent-sized krill. Maximum rates were determined on acclimated krill in large containers during alternating 1-d periods with and without food. During the feeding periods in saturating food concentrations, the mean daily ration was ϳ32% of body carbon d Ϫ1 and excretion was 210% (October-November) and 280% (January) of the values for freshly caught krill. This equates to a maximum loss of ϳ2% of body nitrogen d Ϫ1 . Excretion rates decreased during the 1-d periods without food, and rates during the feeding periods were ϳ30% higher than in those without food. This suggests that the lack of feeding in traditional experiments leads to roughly 30% underestimates of excretion rate. These results help to set some limits on ammonium production rates of South Georgia krill over regional scales. Our calculations suggest that the role of krill in this varies between habitats to the west of the island (insignificant) and those in the east (significant).

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Excretion In Relation To Feeding-mentioning

confidence: 99%

Section: Excretion In Relation To Feeding-mentioning

confidence: 99%

mentioning

confidence: 99%

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Ammonium excretion by Antarctic krill Euphausia superba at South Georgia

Atkinson

Whitehouse

2000

Limnology & Oceanography

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Aspects of the study of the life cycles of Antarctic copepods

Schnack-Schiel

Copepoda: Developments in Ecology, Biology and Systematics

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Different approaches to the study of life cycle strategies of Antarctic copepods are described in an attempt to shed new light on our present knowledge. To date, most studies were carried out on abundance, horizontal and vertical distribution and stage composition during different seasons and in various regions. Hence, the seasonal pictures had to be compiled from different years and sampling regions. The physiological method includes measurements on e.g. egg production, feeding, respiration and excretion rates, C:N and O:N ratios, lipid and protein contents. However, both physiological and biochemical data are still rare. Results of field observations are given in this paper for investigations conducted within the last 15 years in the eastern Weddell Sea, while data of physiological parameters are based on a broader geographical region. In the eastern Weddell Sea, eight copepod species account for about 95% of copepod abundance and for more than 80% of copepod biomass. Within the calanoids, the small species Microcalanus pygmaeus dominates by numbers with 66%, while the large species Calanoides acutus and Calanus propinquus comprise together 52% of the biomass. Species abundance is lowest in winter and highest in summer/autumn, however, seasonal changes in the abundance of M. pygmaeus are small and this species occurs in similar quantities throughout the year. All copepod species show a distinct seasonal vertical distribution pattern and they occur in upper water layers in summer, in contrast to the other seasons. However, the depth layers of maximum concentration differ between species. The ontogenetic vertical migration is most pronounced in C. acutus and relatively weak in C. propinquus. The age structure also shows seasonal differences with the youngest population observed in summer for C. acutus, C. propinquus, Ctenocalanus citer or autumn for Metridia gerlachei, whereas the M. pygmaeus population is oldest during summer. The youngest copepodite stage and the males are not always present in C. acutus and C. propinquus. In contrast, all developmental stages and both sexes occur throughout the year in M. gerlachei, M. pygmaeus and C. citer. Gonad maturation in the dominant calanoid species proceeds well before the onset of phytoplankton production in the eastern Weddell Sea. However, the highest portion of females with ripe gonads and hence highest egg production rates coincide with the productive period in spring and summer. In autumn, ovaries of the three larger species C. acutus, C. propinquus and M. gerlachei are all spent. In contrast, the percentage of ripe females of the two smaller species, C. citer and M. pygmaeus, stays high in autumn. Egg production rates are highly variable within one region and species. Many copepods accumulate large depots of lipid, mainly wax esters. In contrast, five species (C. propinquus, C. simillimus, Euchirella rostromagna, Stephos longipes and Paralabidocera antarctica) almost exclusively synthesise triacylglycerols and not wax esters. The lipid content exhibits ...

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