Biological studies of antarctic krill, austral summer, 1977-1978
Extensive blooms of Phaeocystis (Haptophycea; Prymnesiales) were encountered off the Ross Ice Shelf at stations 10 through 15 (see map). The bloom extended from at least 167°E. to 164°W. and from 78°27'S. to about 76°S. At all stations in the area, Phaeocystis was so abundant that it clogged the zooplankton nets before they had filtered more than 30 cubic meters. Phaeocystis was not restricted to the 21-meter euphotic zone, but was present to depths of 100 to 150 meters. To determine the uptake of glycolic acid under naturally simulated conditions, uniformly labeled C14 glycolic acid was inoculated into subsamples for simulated and in situ incubation (Parsons et al., 1977). These experiments will be used to determine the fate of extracellular phytoplankton metabolites and a possible relation to heterotrophic bacterial biomass. Autoradiography will be used to identify the organisms involved in heterotrophic uptake of glycolic acid (Munro and Brock, 1968). Krill (Euphausia superba) were not common at stations occupied during this cruise, but a congeneric species of euphausiid (E. crystallorophio.$) was present at all stations south of the Polar Front and at subantarctic station 2. Except for numerous tiny larvaceans and chaetognaths, gelatinous zooplankton were rare. Hyperiid amphipods (primarily Parathemisto) were abundant at the subantarctic stations, but in the Ross Sea species of gammarid amphipods predominated. Rates of oxygen consumption and NH 4 + excretion were measured at each station for individual organisms of the more abundant and larger sized zooplankton groups, in containers of filtered sea water (see table). Subantarctic species (stations 1 and 2) were used in 34 experiments and 66 experiments were conducted with species collected south of the Polar Front. As shown in the table, weight-specific NH 4 + excretion and oxygen consumption rates were uniformly higher at the stations north of the Polar Front than at the Ross Sea stations. However, ratios of atoms of oxygen consumed to atoms of NH 4 + excreted (O:NH 4 * ratios) were not significantly different (95 percent confidence level) between subantarctic and antarctic zooplankton. Gymnosome pteropods showed high O:NH 4 ratios, which reflect their very low rates of NH 4 + excretion (Biggs, 1977). O:NH 4 + ratios for other zooplankton averaged 12 to 31 (see table). This suggests that protein catabolism may account for 50 percent or more of zooplankton metabolism (Harris, 1959; Ikeda, 1974). Respiratory quotients measured by McWhinnie and others (1975, 1976) suggest that lipogenesis is quite significance, as well. Another Texas A&M research activity carried out during the 1977-78 austral summer was conducted by M. Meyer at Palmer Station, Anvers Island. Grazing experiments with krill (Euphausia superba) feeding on natural phytoplankton populations were conducted in cooperation with Mary Alice McWhinnie's krill study (see p. 133 in this issue). During each experiment, changes in cell number, dry weight, carbon, chlorophyll a, phaeopigments, oxygen, and ammonia were monitored. Preliminary analysis of these data suggest O:NH 4 + ratios of 19, which are comparable to the values measured for euphausiids from the Ross Sea cruise. Four additional krill grazing experiments were conducted to determine the ingestion rates of C14 labeled phytoplankton (Lasker, 1966), which were isolated and cultured at Palmer Station. The antarctic phytoplankton cultures will be continued at Texas A&M University for taxonomic and physiological studies. October 1978
References
Biggs, D. C. 1977. Respiration and ammonium excretion by open ocean gelatinous zooplankton. Limnology and Oceanography, 22: 108-117. El-Sayed, S. Z., and S. Taguchi. 1977. Phytoplankton studies in the water column and in the pack ice of the Weddell Sea. Antarctic Journal of the Us., 12: 35-36. Harris, E. 1959. The nitrogen cycle in Long Island Sound. Bulletin of Bingham Oceanography, 17: 31-65. Ikeda, T. 1974. Nutritional ecology of marine zooplankton. Memoirs of the Faculty of Fisheries, Hokkaido University, 22: 1-97. Kiefer, D. A., RJ. Olson, and 0. Holm-Hansen. 1976. Another look at the nitrite and chlorophyll maxima in the central North Pacific. Deep Sea Research, 23: 1199-1208. Lasker, R 1966. Feeding, growth, respiration and carbon utilization of a Euphausiid crustacean. Journal of Fisheries Research Board, Canada, 23: 1291-1317. McWhinnie, M. A., and C. J. Denys. 1978. Biological studies of Antarctic krill, austral summer, 1977-1978. Antarctic Journal of the US., 13(4): 133-135. McWhinnie, M. A., C.J. Denys, and D. Schenborn. 1976. Biology of krill (Euphausia superba) and other antarctic invertebrates. Antarctic Journal of the US., 11: 55-58. McWhinnie, M. A., S. Rakusa-Suszczewski, and M. 0. Cahoon. 1975. Physiological and metabolic studies of antarctic fauna, austral 1974 winter at McMurdo station. Antarctic Journal of the US., 10: 293-297. Munro, A. L. A., and T. D. Brock. 1968. Distribution between bacterial and algal utilization of soluble substances in the sea.Journal of General Microbiology, 51: 35-42. Packard, T. T., R. C. Dugdale,J.J. Goering, and R. T. Barber. 1978. Nitrate reductase activity in the subsurface waters of the Peru Current.Journal of Marine Research, 36: 59-76. Parsons, R. T., M. Takahashi, and B. Hargrave. 1977. Biological Oceanographic Processes (2nd ed.). Pergamon Press, New York. Steemann Nielsen, E. 1952. The use of radioactive carbon (C14) for measuring organic production in the sea.Journal du Conseil, Conseil International pour l'Exploration de la Mer, 18: 117-140.
Biological studies of antarctic krill, austral summer, 1977-1978 M. A. MCWHINNIE and C.J. DENYS Department of Biological Sciences De Paul University Chicago, Illinois 60614
Our study of the biology of krill, Euphausia superba, continued at Palmer Station from 4 December 1977 to 28 March 1978. Two new krill laboratories provided the first opportunity to maintain large stocks of living planktonic animals over long periods (see figure 1). These wet-laboratories are 133
I U I! ,/ 1•
;4
Figure 2. View of part of the 11-foot-long seawater tank in which stock krill are maintained and behavioral studies are conducted. In this photo, krill are aggregating under a dim red light source.
Figure 1. Two krill aquarium buildings behind the main laboratory building at Palmer Station. These are joined by a light-tight anteroom which allows entrance to the aquaria without changing the internal light conditions. A flow-through sea water system services both buildings.
DEVELOPMENTAL STAGE
MITANAUPLIUS (MOLT) TRANSITIONS TO 2nd NAUPLIUS
—
1 52 NAUPLIUS HATCHING
LIMB PRIMORDIA GASTRULA LATE
—
RAlLY
—
Figure 3. Rate of develop mental advance of Euphausia superba from eggs spawned In the laboratory and reared to metanauplius.
SLASTULA — 32 -CELL 16-CELL — $-CELL — 4-CILL — 2-CILL —
Ii
i I i I i 24 48 72 96j[ S HOURS
IL
it
DAYS
TIME AFTER SPAWNING
equipped with all-glass aquaria (two measuring 3.34 by 0.6 by 0.6 meters, one 1.7 by 0.6 by 0.6 meters, and four smaller tanks), and automatic light control (see figure 2). Stocks from (a) the eastern Bellingshausen Sea and (b) the Bransfield Straits and area channels and passages were maintained separately. Field sampling was conducted aboard RJV Hero throughout the season (2 December 1977 to 24 March 1978) between the southern Gerlache Strait (640 43'S.63° 10'W.)
134
allIllIll Ii
7 9 11 13 15 17
and Danger Islands (63 0 20'S.54°50'W.). Collections in the eastern Bellingshausen Sea were made at the same locations every 3 to 4 weeks. The knit study was broad in scope: it included spawning and development of young, molting and its relation to growth rate and longevity, feeding habits and thei relation to seasonal growth, and the behavioral role of light. Light responses and visual pigment characteristics were investigated in relation to swarming behavior and diurnal vertical migration
ANTARCTIC JOURNAL
(figure 2). Potential population differences were also studied with krill from the two regions sampled. Animals collected (2 December) in the Bellingshausen Sea included mature females; the first spawning in the laboratory occurred 20 December. Spawning females were isolated throughout the summer, and development was studied repeatedly with larvae reared in the laboratory. This study establishes that high hydrostatic pressure, as exists at great depths in the water column, is not necessary for spawning or normal development as previously thought. The time scale (figure 3) and developmental events from fertilized egg to metanauplius larva are now known, as is the fecundity of this species. Post-spawned females were maintained to study their viability and longevity. These animals molt at appropriate intervals and assume a premature condition showing normal feeding and viability. The change to an apparent younger stage after spawning is responsible for the conclusion that post-spawn females most probably die, because they are rarely found in populations collected throughout the austral summer and early fall. Krill representing a wide size range were isolated in 0.5and 1.0-liter containers (170 animals) and kept 4 months to study molting frequency and growth with each molt. Phytoplankton collected in Arthur Harbor served as the food source for these animals. Because crustaceans undergo "shock molting" when taken from their normal environment, the intermolt interval for knIt was studied after the initial burst of molting that occurred for several days after transfer to laboratory aquaria from live-boxes on R/v Hero, from which all collections were made. Growth increments were determined by measuring the uropod of the shed exoskeleton. By regression correlation of uropod length vs. body length, the equation so derived was used to determine linear growth or length differentials at each molt. With these data, growth rates through late spring to early fall can now be computed and longevity more accurately estimated. The data support the empirical hypothesis that time to maturity is considerably greater than 2 years if molting and growth do no occur in winter. The opportunity to maintain a large and healthy stock of these planktonic animals permitted observations of their feeding behavior. Stock-animal aquaria were provided with a seawater flow of approximately 300 liters per hour. These animals, conducting filtering movements continuously, showed a sustained phytoplankton feeding level by the intensity of green throughout their digestive tract and by fecalstring production. With the seasonal decline of phytoplankton in early February and onward, they became light green, in general. This index of feeding, as well as other data, had been the basis for the designation of this species as an exclusive herbivore. However, careful observation throughout these 4 months revealed that cannibalism among knit is relatively common. In addition, these animals, feed on other zoopiankton. On the basis of data from this study, then, Euphausia superba must be classified as omnivorous and predatory as are the majority of other euphausiid species. These new data require revisions of estimations of growth throughout the austral winter, a period of greatly diminished phytoplankton availability during which krill growth previously had been considered negligible. Several thousand krill are being maintained in the knit facility at Palmer Station through austral winter 1978 to determine survivability, growth, advance to maturity, and
October 1978
feeding behavior. This is the first opportunity to study knIt on a year-round basis. We are especially grateful to James Punches, who is conducting this winter study and surveillance. In addition, we gratefully acknowledge the assistance of Robert Picken and Thomas Poleck, whose help made the extent of these studies possible; we are grateful to Michael Myers (Texas A&M University), who joined our program and assisted in many ways. Captain P. Lenie of RJv Hero collected krill and worked with us on many stringent cruises; without his work this broad-based study would not have been possible. This study was supported by grant DPP 77-21747 from the National Science Foundation.
Antarctic krill: ecology and commercial exploitation GERALDJ. BAKUS Tetra Tech, Inc. Pasadena, California 91107 and Allan Hancock Foundation University of Southern California Los Angeles, California 90007 WENDY GARLING andJoHN E. BUCHANAN Tetra Tech, Inc. Arlington, Virginia 22209
The antarctic marine ecosystem is highly productive; it includes 44 bird, 6 seal, and approximately 14 whale species. Diatoms are the dominant phytoplankton and copepods are the dominant small zooplankton. Knit (euphausiids) comprise the basic food of many animals. The density of krill in the Antarctic is believed to be about one individual per cubic meter. The most important of the 11 species of krill are Euphausia superba ( dominant in open waters), E. crystallorophias (dominant under pack ice), Thysanoessa macrura, and E. vallentini. Antarctic krill are basically filter feeders, feeding mostly on diatoms found in surface waters. The largest concentrations of knIt are found in the East Wind Drift zone; the Weddell, Ross, Amundsen, and Bellingshausen Seas; north and east of South Georgia Island; the Scotia Sea north of the Orkney Islands; around the South Shetland Islands; and west of the South Sandwich Islands. Fertilization of krill eggs occurs externally, and the eggs sink. Hatching occurs in deep water, and the developing krill ascend to the surface layers where they congregate and exhibit diurnal vertical migration. Knit fecundity values vary; growth rates vary geographically; Euphausia superba may live for 4 years. KnIt form patchy, dense, but apparently monospecific, aggregations (swarms), possibly the result of
135
References
Biggs, D. C. 1977. Respiration and ammonium excretion by open ocean gelatinous zooplankton. Limnology and Oceanography, 22: 108-117. El-Sayed, S. Z., and S. Taguchi. 1977. Phytoplankton studies in the water column and in the pack ice of the Weddell Sea. Antarctic Journal of the Us., 12: 35-36. Harris, E. 1959. The nitrogen cycle in Long Island Sound. Bulletin of Bingham Oceanography, 17: 31-65. Ikeda, T. 1974. Nutritional ecology of marine zooplankton. Memoirs of the Faculty of Fisheries, Hokkaido University, 22: 1-97. Kiefer, D. A., RJ. Olson, and 0. Holm-Hansen. 1976. Another look at the nitrite and chlorophyll maxima in the central North Pacific. Deep Sea Research, 23: 1199-1208. Lasker, R 1966. Feeding, growth, respiration and carbon utilization of a Euphausiid crustacean. Journal of Fisheries Research Board, Canada, 23: 1291-1317. McWhinnie, M. A., and C. J. Denys. 1978. Biological studies of Antarctic krill, austral summer, 1977-1978. Antarctic Journal of the US., 13(4): 133-135. McWhinnie, M. A., C.J. Denys, and D. Schenborn. 1976. Biology of krill (Euphausia superba) and other antarctic invertebrates. Antarctic Journal of the US., 11: 55-58. McWhinnie, M. A., S. Rakusa-Suszczewski, and M. 0. Cahoon. 1975. Physiological and metabolic studies of antarctic fauna, austral 1974 winter at McMurdo station. Antarctic Journal of the US., 10: 293-297. Munro, A. L. A., and T. D. Brock. 1968. Distribution between bacterial and algal utilization of soluble substances in the sea.Journal of General Microbiology, 51: 35-42. Packard, T. T., R. C. Dugdale,J.J. Goering, and R. T. Barber. 1978. Nitrate reductase activity in the subsurface waters of the Peru Current.Journal of Marine Research, 36: 59-76. Parsons, R. T., M. Takahashi, and B. Hargrave. 1977. Biological Oceanographic Processes (2nd ed.). Pergamon Press, New York. Steemann Nielsen, E. 1952. The use of radioactive carbon (C14) for measuring organic production in the sea.Journal du Conseil, Conseil International pour l'Exploration de la Mer, 18: 117-140.
Biological studies of antarctic krill, austral summer, 1977-1978 M. A. MCWHINNIE and C.J. DENYS Department of Biological Sciences De Paul University Chicago, Illinois 60614
Our study of the biology of krill, Euphausia superba, continued at Palmer Station from 4 December 1977 to 28 March 1978. Two new krill laboratories provided the first opportunity to maintain large stocks of living planktonic animals over long periods (see figure 1). These wet-laboratories are 133
I U I! ,/ 1•
;4
Figure 2. View of part of the 11-foot-long seawater tank in which stock krill are maintained and behavioral studies are conducted. In this photo, krill are aggregating under a dim red light source.
Figure 1. Two krill aquarium buildings behind the main laboratory building at Palmer Station. These are joined by a light-tight anteroom which allows entrance to the aquaria without changing the internal light conditions. A flow-through sea water system services both buildings.
DEVELOPMENTAL STAGE
MITANAUPLIUS (MOLT) TRANSITIONS TO 2nd NAUPLIUS
—
1 52 NAUPLIUS HATCHING
LIMB PRIMORDIA GASTRULA LATE
—
RAlLY
—
Figure 3. Rate of develop mental advance of Euphausia superba from eggs spawned In the laboratory and reared to metanauplius.
SLASTULA — 32 -CELL 16-CELL — $-CELL — 4-CILL — 2-CILL —
Ii
i I i I i 24 48 72 96j[ S HOURS
IL
it
DAYS
TIME AFTER SPAWNING
equipped with all-glass aquaria (two measuring 3.34 by 0.6 by 0.6 meters, one 1.7 by 0.6 by 0.6 meters, and four smaller tanks), and automatic light control (see figure 2). Stocks from (a) the eastern Bellingshausen Sea and (b) the Bransfield Straits and area channels and passages were maintained separately. Field sampling was conducted aboard RJV Hero throughout the season (2 December 1977 to 24 March 1978) between the southern Gerlache Strait (640 43'S.63° 10'W.)
134
allIllIll Ii
7 9 11 13 15 17
and Danger Islands (63 0 20'S.54°50'W.). Collections in the eastern Bellingshausen Sea were made at the same locations every 3 to 4 weeks. The knit study was broad in scope: it included spawning and development of young, molting and its relation to growth rate and longevity, feeding habits and thei relation to seasonal growth, and the behavioral role of light. Light responses and visual pigment characteristics were investigated in relation to swarming behavior and diurnal vertical migration
ANTARCTIC JOURNAL
(figure 2). Potential population differences were also studied with krill from the two regions sampled. Animals collected (2 December) in the Bellingshausen Sea included mature females; the first spawning in the laboratory occurred 20 December. Spawning females were isolated throughout the summer, and development was studied repeatedly with larvae reared in the laboratory. This study establishes that high hydrostatic pressure, as exists at great depths in the water column, is not necessary for spawning or normal development as previously thought. The time scale (figure 3) and developmental events from fertilized egg to metanauplius larva are now known, as is the fecundity of this species. Post-spawned females were maintained to study their viability and longevity. These animals molt at appropriate intervals and assume a premature condition showing normal feeding and viability. The change to an apparent younger stage after spawning is responsible for the conclusion that post-spawn females most probably die, because they are rarely found in populations collected throughout the austral summer and early fall. Krill representing a wide size range were isolated in 0.5and 1.0-liter containers (170 animals) and kept 4 months to study molting frequency and growth with each molt. Phytoplankton collected in Arthur Harbor served as the food source for these animals. Because crustaceans undergo "shock molting" when taken from their normal environment, the intermolt interval for knIt was studied after the initial burst of molting that occurred for several days after transfer to laboratory aquaria from live-boxes on R/v Hero, from which all collections were made. Growth increments were determined by measuring the uropod of the shed exoskeleton. By regression correlation of uropod length vs. body length, the equation so derived was used to determine linear growth or length differentials at each molt. With these data, growth rates through late spring to early fall can now be computed and longevity more accurately estimated. The data support the empirical hypothesis that time to maturity is considerably greater than 2 years if molting and growth do no occur in winter. The opportunity to maintain a large and healthy stock of these planktonic animals permitted observations of their feeding behavior. Stock-animal aquaria were provided with a seawater flow of approximately 300 liters per hour. These animals, conducting filtering movements continuously, showed a sustained phytoplankton feeding level by the intensity of green throughout their digestive tract and by fecalstring production. With the seasonal decline of phytoplankton in early February and onward, they became light green, in general. This index of feeding, as well as other data, had been the basis for the designation of this species as an exclusive herbivore. However, careful observation throughout these 4 months revealed that cannibalism among knit is relatively common. In addition, these animals, feed on other zoopiankton. On the basis of data from this study, then, Euphausia superba must be classified as omnivorous and predatory as are the majority of other euphausiid species. These new data require revisions of estimations of growth throughout the austral winter, a period of greatly diminished phytoplankton availability during which krill growth previously had been considered negligible. Several thousand krill are being maintained in the knit facility at Palmer Station through austral winter 1978 to determine survivability, growth, advance to maturity, and
October 1978
feeding behavior. This is the first opportunity to study knIt on a year-round basis. We are especially grateful to James Punches, who is conducting this winter study and surveillance. In addition, we gratefully acknowledge the assistance of Robert Picken and Thomas Poleck, whose help made the extent of these studies possible; we are grateful to Michael Myers (Texas A&M University), who joined our program and assisted in many ways. Captain P. Lenie of RJv Hero collected krill and worked with us on many stringent cruises; without his work this broad-based study would not have been possible. This study was supported by grant DPP 77-21747 from the National Science Foundation.
Antarctic krill: ecology and commercial exploitation GERALDJ. BAKUS Tetra Tech, Inc. Pasadena, California 91107 and Allan Hancock Foundation University of Southern California Los Angeles, California 90007 WENDY GARLING andJoHN E. BUCHANAN Tetra Tech, Inc. Arlington, Virginia 22209
The antarctic marine ecosystem is highly productive; it includes 44 bird, 6 seal, and approximately 14 whale species. Diatoms are the dominant phytoplankton and copepods are the dominant small zooplankton. Knit (euphausiids) comprise the basic food of many animals. The density of krill in the Antarctic is believed to be about one individual per cubic meter. The most important of the 11 species of krill are Euphausia superba ( dominant in open waters), E. crystallorophias (dominant under pack ice), Thysanoessa macrura, and E. vallentini. Antarctic krill are basically filter feeders, feeding mostly on diatoms found in surface waters. The largest concentrations of knIt are found in the East Wind Drift zone; the Weddell, Ross, Amundsen, and Bellingshausen Seas; north and east of South Georgia Island; the Scotia Sea north of the Orkney Islands; around the South Shetland Islands; and west of the South Sandwich Islands. Fertilization of krill eggs occurs externally, and the eggs sink. Hatching occurs in deep water, and the developing krill ascend to the surface layers where they congregate and exhibit diurnal vertical migration. Knit fecundity values vary; growth rates vary geographically; Euphausia superba may live for 4 years. KnIt form patchy, dense, but apparently monospecific, aggregations (swarms), possibly the result of
135
