Zooplankton metabolic studies in the Ross Sea · Zooplankton samples were dominated by copepods,...
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Zooplankton metabolic studies in the Ross Sea R. R. BIDIGARE Department of Biochemistry and Biophysics Texas A&M University College Station, Texas 77843 J. L. Cox Marine Science Institute University of California Santa Barbara, California 93106 During the period 17-24 January 1982, we participated in an interdisciplinary study aboard USCGC Glacier to define the im- portant environmental and biological factors regulating pri- mary and secondary production in the southwest Ross Sea. Biggs (Antarctic Journal, this issue) has presented an overview of the expedition. Our primary interest was to estimate the impact of ammonium excretion and the grazing potential of the zoo- plankton community, using physiological and biochemical measurement techniques. In addition, we investigated the effects of short-term starvation on the nitrogen metabolism of Euphausia crystallorophias. Zooplankton were sampled at every other station using 70- centimeter BONGO nets (figure) of 333-micrometer mesh hauled vertically from 100 to 0 meters (see Biggs, figure 1, for location of stations). Flow through the nets was estimated using a TSK flowmeter; calibration data were provided by E. Brinton. Vol- umes filtered ranged from 70 to 230 cubic meters per haul. The contents of one of the nets were frozen for biochemical analysis; the contents of the other were preserved in buffered for- maldehyde for subsequent taxonomic identification and wet- weight determination. Zooplankton samples were dominated by copepods, theco- some pteropods, and juvenile euphausids. The 333-micrometer mesh retained quantities of diatoms, with algal displacement volumes reaching tens to hundreds of milliliters per haul in the eastern part of our field area. Preserved zooplankton currently are being sorted for wet-weight measurement. Their biomass (in grams per cubic meter) will be used in conjunction with the weight-specific excretion data from previous studies of Ross Sea zooplankton (Biggs 1982b) to map the zooplankton excretion impact (in micromoles of ammonium per cubic meter per hour) throughout our field area. To estimate the grazing potential of the zooplankton com- munity, laminarinase activity assays will be performed on sub- samples of the material frozen for biochemical analysis. Cox (1981) found that laminarinase activity was useful as an index of grazing potential in temperate euphausids and temperate mixed zooplankton. Laminarinase activities will be normalized by volume filtered per haul and then compared with the average chlorophyll concentration at each of the zooplankton sampling stations. The effect of starvation on the nitrogen metabolism of E. crystallorophias was investigated by measuring changes in pro- tein content, rates of ammonium excretion, and glutamate de- hydrogenase activity after 2 days of maintenance in filtered seawater. Previous studies have show n\'that glutamate de- hydrogenase activity is linked to rates of ammonium excretion in temperate crustaceans (Bidigare and King 1,981), subtropical zooplankton (Bidigare, King, and Biggs in pess), and antarctic zooplankton (Bidigare et al. 1981). The table presents the results of the starvation experiment. Adult euphausids averaging 200 milligrams in wetweight were used. Immediately after capture, excretion rates averaged 0.14 mi- cromole of ammonium per individual per hour, equivalent to the values that Biggs and Bidigare (1981) and Biggs (1982b) predicted for euphausids collected in the Scotia Sea and the Ross Sea, respectively. Excretion rates decreased significantly (p = 0.037), by an average of 57 percent, after the 2-day starvation period. Body protein also decreased signficantly (p 0.003), by an average of 24 percent in 2 days. Catabolism of body protein provides a source of energy in the form of adenosine triphos- phate and a means of satisfying metabolic nitrogen require- ments during short-term starvation. Ikeda and Skjoldal (1980) reported decreases of 33 percent and 34 percent in the am- monium excretion and protein content of subtropical copepods maintained for 2 days in laboratory aquaria. Glutamate dehydrogenase activities measured in E. crys- tallorophias also decreased significantly (p = 0.032), by an aver- mew The BONGO net system used aboard USCGC Glacier to collect zoo- plankton samples. 1982 REVIEW 153
Transcript of Zooplankton metabolic studies in the Ross Sea · Zooplankton samples were dominated by copepods,...
Zooplankton metabolic studies in theRoss Sea
R. R. BIDIGARE
Department of Biochemistry and BiophysicsTexas A&M University
College Station, Texas 77843
J. L. Cox
Marine Science InstituteUniversity of California
Santa Barbara, California 93106
During the period 17-24 January 1982, we participated in aninterdisciplinary study aboard USCGC Glacier to define the im-portant environmental and biological factors regulating pri-mary and secondary production in the southwest Ross Sea.Biggs (Antarctic Journal, this issue) has presented an overview ofthe expedition. Our primary interest was to estimate the impactof ammonium excretion and the grazing potential of the zoo-plankton community, using physiological and biochemicalmeasurement techniques. In addition, we investigated theeffects of short-term starvation on the nitrogen metabolism ofEuphausia crystallorophias.
Zooplankton were sampled at every other station using 70-centimeter BONGO nets (figure) of 333-micrometer mesh hauledvertically from 100 to 0 meters (see Biggs, figure 1, for location ofstations). Flow through the nets was estimated using a TSKflowmeter; calibration data were provided by E. Brinton. Vol-umes filtered ranged from 70 to 230 cubic meters per haul. Thecontents of one of the nets were frozen for biochemical analysis;the contents of the other were preserved in buffered for-maldehyde for subsequent taxonomic identification and wet-weight determination.
Zooplankton samples were dominated by copepods, theco-some pteropods, and juvenile euphausids. The 333-micrometermesh retained quantities of diatoms, with algal displacementvolumes reaching tens to hundreds of milliliters per haul in theeastern part of our field area. Preserved zooplankton currentlyare being sorted for wet-weight measurement. Their biomass(in grams per cubic meter) will be used in conjunction with theweight-specific excretion data from previous studies of Ross Seazooplankton (Biggs 1982b) to map the zooplankton excretionimpact (in micromoles of ammonium per cubic meter per hour)throughout our field area.
To estimate the grazing potential of the zooplankton com-munity, laminarinase activity assays will be performed on sub-samples of the material frozen for biochemical analysis. Cox(1981) found that laminarinase activity was useful as an index ofgrazing potential in temperate euphausids and temperatemixed zooplankton. Laminarinase activities will be normalizedby volume filtered per haul and then compared with the averagechlorophyll concentration at each of the zooplankton samplingstations.
The effect of starvation on the nitrogen metabolism of E.crystallorophias was investigated by measuring changes in pro-tein content, rates of ammonium excretion, and glutamate de-hydrogenase activity after 2 days of maintenance in filtered
seawater. Previous studies have show n\'that glutamate de-hydrogenase activity is linked to rates of ammonium excretionin temperate crustaceans (Bidigare and King 1,981), subtropicalzooplankton (Bidigare, King, and Biggs in pess), and antarcticzooplankton (Bidigare et al. 1981). The table presents the resultsof the starvation experiment. Adult euphausids averaging 200milligrams in wetweight were used.
Immediately after capture, excretion rates averaged 0.14 mi-cromole of ammonium per individual per hour, equivalent tothe values that Biggs and Bidigare (1981) and Biggs (1982b)predicted for euphausids collected in the Scotia Sea and theRoss Sea, respectively. Excretion rates decreased significantly (p= 0.037), by an average of 57 percent, after the 2-day starvationperiod. Body protein also decreased signficantly (p 0.003), byan average of 24 percent in 2 days. Catabolism of body proteinprovides a source of energy in the form of adenosine triphos-phate and a means of satisfying metabolic nitrogen require-ments during short-term starvation. Ikeda and Skjoldal (1980)reported decreases of 33 percent and 34 percent in the am-monium excretion and protein content of subtropical copepodsmaintained for 2 days in laboratory aquaria.
Glutamate dehydrogenase activities measured in E. crys-tallorophias also decreased significantly (p = 0.032), by an aver-
mew
The BONGO net system used aboard USCGC Glacier to collect zoo-plankton samples.
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the Scripps Institution of Oceanography, University of Califor-nia-San Diego, for supplying BONGO nets and for confirmingthe identification of E. crystallorophias.
Effect of short-term starvation on the nitrogen metabolism of E.crystallorophias
Days of starvation
0 2
Protein content (milligramsper individual)
19.4 ± 0.3 (2)14.8 ± 0.2 (2)Ammonium excretion rate (ml-
cromoles of ammonium perindividual per hour)'
0.14 ± 0.01(2)0.06 ± 0.02(2)Glutamate dehydrogenase ac-
tivity (micromoles of am-monium per individual perhour)' 13.6 ± 0.8 (2)9.6 ± 0.6 (2)
a Figures show means ± 1 standard deviation; figures in parentheses arenumbers of experiments performed.
b Measured at O'C; 3-6 individuals per experiment.c Measured at 10'C; 3-6 individuals per experiment.
age of 29 percent. This confirms the finding that glutamatedehydrogenase activities are linked to rates of ammonium ex-cretion in boreal crustaceans and extends to the southern oceanenvironments the utility of glutamate dehydrogenase as anindex of ammonium excretion.
This research was supported by National Science Foundationgrants DE'I' 79-21355 and DPP 80-20739. We thank E. Brinton of
References
Bidigare, R. R., Johnson, M. A., Guffy, J . D., and Biggs, D. C. 1981.Nutrient chemistry of ammonium in antarctic surface waters. Antarc-tic Journal of the U.S., 16(5), 168-170.
Bidigare, R. R., and King, F. D. 1981. The measurement of glutamatedehydrogenase activity in Praunus flexuosus and its role in the regula-tion of ammonium excretion. Comparative Biochemistry and Physiology,70B, 409-413.
Bidigare, R. R., King, F. D., and Biggs, D. C. In press. Glutamatedehydrogenase (CDII) and respiratory electron-transport-system(ET5) activities in Gulf of Mexico zooplankton. Journal of PlanktonResearch.
Biggs, D. C. 1982. Ross Sea ammonium flux experiment. AntarcticJournal of the U.S., 17(5). (a)
Biggs, D. C. 1982. Zooplankton excretion and NH 4*cycling in near-surface waters in the southern ocean. I. Ross Sea, austral summer1977-1978. Polar Biology, 1, 55-67. (b)
Biggs, D. C., and Bidigare, R. R. 1981. Oceanograpic studies of epipelagicamnonium dynamics in the Scotia Sea, Islas Orcadas cruises 17 and 19(Tech. Rep. 814-T). College Station: Texas A&M University, Depart-ment of Oceanography.
Cox, J. L. 1981. Laminarinase induction in marine zooplankton and itsvariability in zooplankton samples. Journal of Plankton Research, 3,345-355.
Ikeda, T., and Skjoldal, H. 1980. Effect of laboratory conditions on theextrapolation of experimental measurements to the ecology of marinezooplankton. VI. Changes in physiological activities and biochemicalcomponents of Acetes sibogae australis and Acartia oust ralis after cap-ture. Marine Biology, 58, 285-293.
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