Heterotrophic activities in the marine surface waters
While the high phytoplankton biomass values of the 1983 study are characteristic of bloom conditions, the low biomass values of the 1986 study indicate that any bloom which might have been associated with the ice-edge was dissipated by the time of our study. Bloom situations in the marginal ice zone of the southern oceans are initiated and maintained by meltwaterinduced stratification of the water column (Smith and Nelson 1985). The spatial and temporal limitation of these blooms is controlled by the presence or absence of this stability. However, results from the 1986 study show that vertical mixing of surface waters was limited to 40 or 50 meters by a strong halo- and pycnocline (Muench and Husby, Antarctic Journal, this issue). Such stability was not correlated with phytoplankton distribution. These low values are in contrast to high phytoplankton standing stocks measured in 1983 during a period in which the receding ice edge had a much deeper mixed layer (mean of 57 meters, range 10-130 meters; Smith and Nelson 1986).
Heterotrophic activities in the marine surface waters near penguin rookeries of the Antarctic Peninsula R.P. HERWIG and J.T. STALEY Department of Microbiology and immunology SC-42 University of Washington Seattle, Washington 98195 J.S. MAKI Engineering Sciences Laboratory Harvard University Cambridge, Massachusetts 02138
The chlorophyll concentration (algal biomass) and primary productivity of the marine surface waters surrounding the Antarctic Peninsula have been previously studied (El-Sayed 1967). These waters are known to be very productive and support large populations of herbivorous krill, which in turn support several species of krill-feeding birds and mammals. In this study, the bacterial concentrations, heterotrophic activities, and the chlorophyll a concentrations were determined in the surface waters along a transect in the vicinity of Palmer Station (64°46'S 6°3'W), Antarctica. Using the U.S. Coast Guard Arctic Survey Boat, water samples were collected using Niskin 5-liter sampling bottles (General Oceanics) from five stations positioned on a transect from Humble Island out to the deeper waters found in a basin (see figure). Penguins found in rookeries on the small islands (i.e., Lithfield, Torgersen, and Humble Islands) were known to follow this route while feeding for krill and nesting during the 164
This research was supported by National Science Foundation grant DPP 84-20213. References El-Sayed, S.Z., and S. Taguchi. 1981. Primary productivity and standing crop of phytoplankton along the ice edge in the Weddell Sea. Deep-Sea Research, 28, 1017-1032. Muench, R.D., and D.M. Husby. 1986. Physical oceanographic observations carried out as part of the Antarctic Marine Ecosystems Research in the Ice-Edge Zone program, March 1986. Antarctic Journal of the U.S., 21(5). Smith, W.O., and D.M. Nelson. 1985. Phytoplankton bloom produced by a receding ice edge in the Ross Sea: Spatial coherence with the density field. Science, 227, 163-166. Smith, W.O. and D.M. Nelson. 1986. Importance of ice edge phytoplankton production in the Southern Ocean. Bioscience, 362(4), 251-257.
1985-1986 austral summer. Before use, the Niskin bottles were rinsed with a 70 percent ethanol solution. The collected seawater samples were filtered through 100 micrometer Nitex netting to remove the larger zooplankton and particles and placed into sterile 1-liter polypropylene Nalgene bottles. The samples were stored in an ice chest filled with crushed ice until they were processed at the Palmer Station Laboratory. The temperature for the samples was recorded using a hand-held thermometer placed in a bottle containing the collected seawater sample. The chilled samples were transported back to the Palmer Laboratory, and 100-milliliter aliquots were distributed into 18ounce Whirlpak sterile plastic bags. Three bags and a formaldehyde (2 percent, final volume) killed control were incubated at 2.0°C ± 0.5°C with a radioactive substrate for 3 to 5 hours. All radionuclides were purchased from ICN Radiochemicals (Irvine, California). L-glutamic acid, [ 1H] (49 curies per millimole, ICN catalog number 20019-E) and an L-amino acid mixture, [ 3 H] (267 millicuries per milligram, ICN catalog number 20063) were used with the 100 milliliter subsamples. The radioactive amino acid mixture contained the following Lamino acids: alanine, arginine, aspartic acid, giutamic acid, glycine, histidine, isoleucine, leucine, lysine, phenylalanine, proline, serine, threonine, tyrosine, and valine. The specific activity for each amino acid ranged from 25 to 58 curies per millimole and the relative proportion of each amino acid is similar to the proportions found in a typical algal protein hydrolysate (ICN information). For our study, a working solution of the substrates was prepared by dilution of the stock solution 1/20 with autoclaved and 0.2 micrometer filtered distilled water. Fifty microliters of the working solution was added to each Whirlpak bag for each station. The incubations were terminated by filtering the samples through a 47-millimeter diameter, 0.2-micrometer Nuclepore polycarbonate membrane filter at 200 Torr vacuum. The filters were then rinsed five times with ice-chilled 0.2-micrometer filtered and autoclaved seawater. The slightly damp filters were transferred into 20-milliliter glass scintillation vials, 1.0 milliliter of Protosol (New England Nuclear) was added, and the ANTARCTIC JOURNAL
Location of stations for 26 April 1986 transect.
vials were placed in a 50°C waterbath for 10 minutes to dissolve filters were acidified with 50 microliters of glacial acetic acid, and 10 milliliters of Econofluor-2 (New England Nuclear) was added. The vials were shaken and the amount of radioactivity collected on the filters was measured using the Palmer Station LKB 1217 Rackbeta Liquid Scintillation Counter. Counts were corrected for quenching using an external standard ratio procedure. Using this sensitive assay the turnover time for glutamic acid and the amino acid mixture was calculated by using the formula t/f where "t" equals the time of incubation with the radionuclide for each sample, and "f" equals the fraction of the radionuclide that was assimilated by microorganisms present in the sample (Azam and Holm-Hansen 1973). The chlorophyll a concentration of the samples was determined by filtering 500-milliliter aliquots through 4.25-centimeter CF/F Whatman glass fiber filters. Three replicates were used for each sample. The filters were frozen at -60°C until the analyses were performed. Photosynthetic pigments were extracted with methanol and the concentration of chlorophyll a was measured using a Turner Designs 10-005R Fluorometer
(Holm-Hansen and Rieman 1978). Chlorophyll a concentration was corrected for the presence of phaeophytin a. A set of water samples was fixed with 2 percent (final volume) formaldehyde and returned to Seattle for enumeration of bacteria using the acridine orange direct count (AoDc) procedure. Portions of the fixed samples were vacuum-filtered (200 Torr) onto 25-millimeter diameter black 0.2 micrometer Nuclepore membrane filters. The filters were air-dried and stained with an acridine orange solution (30 micrograms per milliliter acridine orange in 0.01 M TAPS (tris[hydroxymethyl]aminopropanesulfonic acid buffer at pH 8.2 with methiolate added as a preservative at 100 micrograms per milliliter and glycerin added at 5 percent final volume). The stained cells were counted using a microscope with epifluorescent illumination. The table lists the data that were collected for the transect performed on 26 February 1986. The counts of bacteria measured by the AODC method ranged from 1.5 x 105 to 2.1 X 106 cells per milliliter. The particulate chlorophyll a concentration was highest in the 10- and 25-meter samples (1.09 to 2.12 milligrams per cubic meter) and reduced in the deeper 100 and 200
Data collected on 26 February 1986 transect Turnover Time (hours) Water Sampling depth depth Water Amino acid Glutamic Station (in meters) (in meters) temperature mixture acid
7 8 8 8 8
32 32 31 31 119 100 274 274 274 274
1986 REVIEW
10 25 10 25 10 10 10 25 100 200
2.2 1.8 2.0 1.9 2.5 2.5 2.2 2.3 1.6 1.4
Acridine orange Chiorophy a direct count (milligrams per (cells per milliliter) cubic meter)
215 206 1241 657 112 68 585 362 708 381 78 75 892 809 854 751 2685 2079 4225 4249
7.9 x 10 2.8 x 10 9.5 x 10 6.9 x 10 1.2 x 106 2.1 x106 1.3x 106 7.3 x 10 2.3 x 10 1.5x 10
1.28 1.09 1.22 1.51 1.23 1.13 2.12 2.27 0.47 0.39
165
samples at station 8 (0.47 and 0.39 milligrams per cubic meter). In the surface waters, the assimilation of the amino acid mixture and glutamic acid was also the greatest for the 10-meter samples collected at stations 7, 4, and 1. Samples collected at these stations had turnover times of 75 to 206 hours for glutamic acid and 78 to 215 hours for the amino acid mixture. These turnover times are comparable to assimilation rates found for leucine and glucose for the more productive areas of McMurdo Sound (Hodson et at. 1981). Although the 10- and 25-meter samples from station 8 contained the highest concentrations of chlorophyll a, these samples did not have the shortest turnover times for the organic compounds that were examined. This result suggests that heterotrophic activity in the surface waters in the vicinity of Palmer Station is not totally dependent upon the algal biomass that is present. The small islands near the station, especially those with rookeries, may be contributing substantial amounts of nutrients to the surface waters. For example, Torgersen Island is reported to have a penguin population of approximately 8,000 breeding pairs of Adélie penguins during the austral summer (Heimark and Heimark 1984). Adult penguins leave the rookeries to collect krill and return to feed chicks who remain at the rookeries from hatching in November until late summer. In addition, penguin excreta from the rookeries are a rich source of phosphate, ammonia, and organic carbon (Ugolini 1972; Speir and Cowling 1984). Nutrients and microorganisms associated with the excreta and ornthithogenic soil may be washing into the surrounding marine waters and thereby enhancing heterotrophic activity and productivity.
Microalgae at the ice edge in the northern Weddell Sea G.A. FRYXELL Department of Oceanography Texas A&M University College Station, Texas 77843-3146
Species of microalgae clearly respond to the changes at the edge of the ice, not only in the ice but also in the water column. In the austral fall of the 1986 season, the iIv Melville and the U.S. Coast Guard icebreaker Glacier visited the accreting ice edge. Our findings were in marked contrast to those found in the austral spring cruises of the U.S. Coast Guard icebreaker Westwind and the Wv Melville in 1983. In the austral fall, those microalgae in the phytoplankton that could make resting spores had done so, and auxospores and maximum size of individual cells showed that the sexual cycle of several species may be triggered by the ice edge or processes associated with it. The sparse population was generally dominated by many diatom species, but the prymnesiophyte Phacocystis was well represented. Phytoplankton abundance was low in the fall, both 166
We would like to acknowledge the excellent cooperatin that we received from the crew of the U.S. Coast Guard Arctic Survey Boat and the support personnel from ITT Antarctic Services, Inc. at Palmer Station. This work was supported by National Science Foundation grant DPP 84-15069.
References
Azam, F., and 0. Holm-Hansen. 1973. Use of tritiated substrates in the study of heterotrophy in seawater. Marine Biology, 23, 191-196. El-Sayed, S.Z. 1967. On the productivity of the southwest Atlantic Ocean and the waters west of the Antarctic Peninsula. In C. Llano and W. Schmitt (Eds.), Biology of the Antarctic seas. (III. Antarctic Research Series, Vol. 11.) Washington, D.C.: American Geophysical Union. Heimark, G.M., and R.J. Heimark. 1984. Birds and marine mammals in the Palmer Station area. Antarctic Journal of the U.S., 19(4), 3-8.
Hodson, R.E., F. Azam, A.F. Carlucci, J.A. Fuhrman, D.M. Karl, and 0. Holm-Hansen. 1981. Microbial uptake of dissolved organic matter in McMurdo Sound, Antarctica. Marine Biology, 61, 89-94. Holm-Hansen, 0., and B. Riemann. 1976. Chlorophyll a determination: Improvements in methodology. Oikos, 30, 438-447. Speir, T.W., and J.C. Cowling. 1984. Ornithogenic soils of the Cape Bird Adélie penguin rookeries, Antarctica. 1. Chemical properties. Polar Biology, 2, 199-205.
Ugolini, F.C. 1972. Ornithogenic soils of Antarctica. In C. Llano (Ed.), Antarctic terrestrial biology. (Antarctic Research Series, Vol. 10) Washington, D.C.: American Geophysical Union.
outside the ice and under it. Since the ice had been concentrated by strong easterly winds during the previous month into a north-south boundary, the adjacent water regimes probably had much the same history of partial ice cover. Salps were common under the ice only. Results from the fall cruises with collections by R.W. Gould, Jr., M.A. Hoban, and G.A. Fryxell, will be reported at a later date, but the two seasons showed many obvious differences. For example, in the austral spring of 1983, the ice edge had begun to retreat and was in loose bands. There was a welldefined upper water column about 50 meters thick (AMERIEZ group in preparation), as in the fall, and the phytoplankton under the ice was low in numbers. However, in the spring outside the ice edge, nets clogged under near-bloom conditions, dominated by two gelatinous colony-forming species: the centric diatom Thalassiosira gravida Cleve and the prymnesiophyte Phaeocystis poucheti (Hariot) Lagerheim (Fryxell, Gould, and Watkins 1985). T. gravida was all but lacking in the ice (Buck, Garrison, and Fryxell 1985) and under the ice, but increased greatly outside the ice beyond station 19 (figure 1) at most depths, and it continued to dominate the diatoms in net hauls taken on the Wv Melville away from the ice. It is proposed that Thalassiosira was seeded from the north, perhaps from subsurface layers, and Phaeocystis from the ice-covered waters or the ice itself (Fryxell in preparation.) The pennate diatom genus Nitzschia was also abundant (figure 2), but the great increase in phytoplankton outside the ice can be credited mainly to the centric diatom. Cell ANTARCTIC JOURNAL
Heterotrophic activities in the marine surface waters near penguin rookeries of the Antarctic Peninsula R.P. HERWIG and J.T. STALEY Department of Microbiology and immunology SC-42 University of Washington Seattle, Washington 98195 J.S. MAKI Engineering Sciences Laboratory Harvard University Cambridge, Massachusetts 02138
The chlorophyll concentration (algal biomass) and primary productivity of the marine surface waters surrounding the Antarctic Peninsula have been previously studied (El-Sayed 1967). These waters are known to be very productive and support large populations of herbivorous krill, which in turn support several species of krill-feeding birds and mammals. In this study, the bacterial concentrations, heterotrophic activities, and the chlorophyll a concentrations were determined in the surface waters along a transect in the vicinity of Palmer Station (64°46'S 6°3'W), Antarctica. Using the U.S. Coast Guard Arctic Survey Boat, water samples were collected using Niskin 5-liter sampling bottles (General Oceanics) from five stations positioned on a transect from Humble Island out to the deeper waters found in a basin (see figure). Penguins found in rookeries on the small islands (i.e., Lithfield, Torgersen, and Humble Islands) were known to follow this route while feeding for krill and nesting during the 164
This research was supported by National Science Foundation grant DPP 84-20213. References El-Sayed, S.Z., and S. Taguchi. 1981. Primary productivity and standing crop of phytoplankton along the ice edge in the Weddell Sea. Deep-Sea Research, 28, 1017-1032. Muench, R.D., and D.M. Husby. 1986. Physical oceanographic observations carried out as part of the Antarctic Marine Ecosystems Research in the Ice-Edge Zone program, March 1986. Antarctic Journal of the U.S., 21(5). Smith, W.O., and D.M. Nelson. 1985. Phytoplankton bloom produced by a receding ice edge in the Ross Sea: Spatial coherence with the density field. Science, 227, 163-166. Smith, W.O. and D.M. Nelson. 1986. Importance of ice edge phytoplankton production in the Southern Ocean. Bioscience, 362(4), 251-257.
1985-1986 austral summer. Before use, the Niskin bottles were rinsed with a 70 percent ethanol solution. The collected seawater samples were filtered through 100 micrometer Nitex netting to remove the larger zooplankton and particles and placed into sterile 1-liter polypropylene Nalgene bottles. The samples were stored in an ice chest filled with crushed ice until they were processed at the Palmer Station Laboratory. The temperature for the samples was recorded using a hand-held thermometer placed in a bottle containing the collected seawater sample. The chilled samples were transported back to the Palmer Laboratory, and 100-milliliter aliquots were distributed into 18ounce Whirlpak sterile plastic bags. Three bags and a formaldehyde (2 percent, final volume) killed control were incubated at 2.0°C ± 0.5°C with a radioactive substrate for 3 to 5 hours. All radionuclides were purchased from ICN Radiochemicals (Irvine, California). L-glutamic acid, [ 1H] (49 curies per millimole, ICN catalog number 20019-E) and an L-amino acid mixture, [ 3 H] (267 millicuries per milligram, ICN catalog number 20063) were used with the 100 milliliter subsamples. The radioactive amino acid mixture contained the following Lamino acids: alanine, arginine, aspartic acid, giutamic acid, glycine, histidine, isoleucine, leucine, lysine, phenylalanine, proline, serine, threonine, tyrosine, and valine. The specific activity for each amino acid ranged from 25 to 58 curies per millimole and the relative proportion of each amino acid is similar to the proportions found in a typical algal protein hydrolysate (ICN information). For our study, a working solution of the substrates was prepared by dilution of the stock solution 1/20 with autoclaved and 0.2 micrometer filtered distilled water. Fifty microliters of the working solution was added to each Whirlpak bag for each station. The incubations were terminated by filtering the samples through a 47-millimeter diameter, 0.2-micrometer Nuclepore polycarbonate membrane filter at 200 Torr vacuum. The filters were then rinsed five times with ice-chilled 0.2-micrometer filtered and autoclaved seawater. The slightly damp filters were transferred into 20-milliliter glass scintillation vials, 1.0 milliliter of Protosol (New England Nuclear) was added, and the ANTARCTIC JOURNAL
Location of stations for 26 April 1986 transect.
vials were placed in a 50°C waterbath for 10 minutes to dissolve filters were acidified with 50 microliters of glacial acetic acid, and 10 milliliters of Econofluor-2 (New England Nuclear) was added. The vials were shaken and the amount of radioactivity collected on the filters was measured using the Palmer Station LKB 1217 Rackbeta Liquid Scintillation Counter. Counts were corrected for quenching using an external standard ratio procedure. Using this sensitive assay the turnover time for glutamic acid and the amino acid mixture was calculated by using the formula t/f where "t" equals the time of incubation with the radionuclide for each sample, and "f" equals the fraction of the radionuclide that was assimilated by microorganisms present in the sample (Azam and Holm-Hansen 1973). The chlorophyll a concentration of the samples was determined by filtering 500-milliliter aliquots through 4.25-centimeter CF/F Whatman glass fiber filters. Three replicates were used for each sample. The filters were frozen at -60°C until the analyses were performed. Photosynthetic pigments were extracted with methanol and the concentration of chlorophyll a was measured using a Turner Designs 10-005R Fluorometer
(Holm-Hansen and Rieman 1978). Chlorophyll a concentration was corrected for the presence of phaeophytin a. A set of water samples was fixed with 2 percent (final volume) formaldehyde and returned to Seattle for enumeration of bacteria using the acridine orange direct count (AoDc) procedure. Portions of the fixed samples were vacuum-filtered (200 Torr) onto 25-millimeter diameter black 0.2 micrometer Nuclepore membrane filters. The filters were air-dried and stained with an acridine orange solution (30 micrograms per milliliter acridine orange in 0.01 M TAPS (tris[hydroxymethyl]aminopropanesulfonic acid buffer at pH 8.2 with methiolate added as a preservative at 100 micrograms per milliliter and glycerin added at 5 percent final volume). The stained cells were counted using a microscope with epifluorescent illumination. The table lists the data that were collected for the transect performed on 26 February 1986. The counts of bacteria measured by the AODC method ranged from 1.5 x 105 to 2.1 X 106 cells per milliliter. The particulate chlorophyll a concentration was highest in the 10- and 25-meter samples (1.09 to 2.12 milligrams per cubic meter) and reduced in the deeper 100 and 200
Data collected on 26 February 1986 transect Turnover Time (hours) Water Sampling depth depth Water Amino acid Glutamic Station (in meters) (in meters) temperature mixture acid
7 8 8 8 8
32 32 31 31 119 100 274 274 274 274
1986 REVIEW
10 25 10 25 10 10 10 25 100 200
2.2 1.8 2.0 1.9 2.5 2.5 2.2 2.3 1.6 1.4
Acridine orange Chiorophy a direct count (milligrams per (cells per milliliter) cubic meter)
215 206 1241 657 112 68 585 362 708 381 78 75 892 809 854 751 2685 2079 4225 4249
7.9 x 10 2.8 x 10 9.5 x 10 6.9 x 10 1.2 x 106 2.1 x106 1.3x 106 7.3 x 10 2.3 x 10 1.5x 10
1.28 1.09 1.22 1.51 1.23 1.13 2.12 2.27 0.47 0.39
165
samples at station 8 (0.47 and 0.39 milligrams per cubic meter). In the surface waters, the assimilation of the amino acid mixture and glutamic acid was also the greatest for the 10-meter samples collected at stations 7, 4, and 1. Samples collected at these stations had turnover times of 75 to 206 hours for glutamic acid and 78 to 215 hours for the amino acid mixture. These turnover times are comparable to assimilation rates found for leucine and glucose for the more productive areas of McMurdo Sound (Hodson et at. 1981). Although the 10- and 25-meter samples from station 8 contained the highest concentrations of chlorophyll a, these samples did not have the shortest turnover times for the organic compounds that were examined. This result suggests that heterotrophic activity in the surface waters in the vicinity of Palmer Station is not totally dependent upon the algal biomass that is present. The small islands near the station, especially those with rookeries, may be contributing substantial amounts of nutrients to the surface waters. For example, Torgersen Island is reported to have a penguin population of approximately 8,000 breeding pairs of Adélie penguins during the austral summer (Heimark and Heimark 1984). Adult penguins leave the rookeries to collect krill and return to feed chicks who remain at the rookeries from hatching in November until late summer. In addition, penguin excreta from the rookeries are a rich source of phosphate, ammonia, and organic carbon (Ugolini 1972; Speir and Cowling 1984). Nutrients and microorganisms associated with the excreta and ornthithogenic soil may be washing into the surrounding marine waters and thereby enhancing heterotrophic activity and productivity.
Microalgae at the ice edge in the northern Weddell Sea G.A. FRYXELL Department of Oceanography Texas A&M University College Station, Texas 77843-3146
Species of microalgae clearly respond to the changes at the edge of the ice, not only in the ice but also in the water column. In the austral fall of the 1986 season, the iIv Melville and the U.S. Coast Guard icebreaker Glacier visited the accreting ice edge. Our findings were in marked contrast to those found in the austral spring cruises of the U.S. Coast Guard icebreaker Westwind and the Wv Melville in 1983. In the austral fall, those microalgae in the phytoplankton that could make resting spores had done so, and auxospores and maximum size of individual cells showed that the sexual cycle of several species may be triggered by the ice edge or processes associated with it. The sparse population was generally dominated by many diatom species, but the prymnesiophyte Phacocystis was well represented. Phytoplankton abundance was low in the fall, both 166
We would like to acknowledge the excellent cooperatin that we received from the crew of the U.S. Coast Guard Arctic Survey Boat and the support personnel from ITT Antarctic Services, Inc. at Palmer Station. This work was supported by National Science Foundation grant DPP 84-15069.
References
Azam, F., and 0. Holm-Hansen. 1973. Use of tritiated substrates in the study of heterotrophy in seawater. Marine Biology, 23, 191-196. El-Sayed, S.Z. 1967. On the productivity of the southwest Atlantic Ocean and the waters west of the Antarctic Peninsula. In C. Llano and W. Schmitt (Eds.), Biology of the Antarctic seas. (III. Antarctic Research Series, Vol. 11.) Washington, D.C.: American Geophysical Union. Heimark, G.M., and R.J. Heimark. 1984. Birds and marine mammals in the Palmer Station area. Antarctic Journal of the U.S., 19(4), 3-8.
Hodson, R.E., F. Azam, A.F. Carlucci, J.A. Fuhrman, D.M. Karl, and 0. Holm-Hansen. 1981. Microbial uptake of dissolved organic matter in McMurdo Sound, Antarctica. Marine Biology, 61, 89-94. Holm-Hansen, 0., and B. Riemann. 1976. Chlorophyll a determination: Improvements in methodology. Oikos, 30, 438-447. Speir, T.W., and J.C. Cowling. 1984. Ornithogenic soils of the Cape Bird Adélie penguin rookeries, Antarctica. 1. Chemical properties. Polar Biology, 2, 199-205.
Ugolini, F.C. 1972. Ornithogenic soils of Antarctica. In C. Llano (Ed.), Antarctic terrestrial biology. (Antarctic Research Series, Vol. 10) Washington, D.C.: American Geophysical Union.
outside the ice and under it. Since the ice had been concentrated by strong easterly winds during the previous month into a north-south boundary, the adjacent water regimes probably had much the same history of partial ice cover. Salps were common under the ice only. Results from the fall cruises with collections by R.W. Gould, Jr., M.A. Hoban, and G.A. Fryxell, will be reported at a later date, but the two seasons showed many obvious differences. For example, in the austral spring of 1983, the ice edge had begun to retreat and was in loose bands. There was a welldefined upper water column about 50 meters thick (AMERIEZ group in preparation), as in the fall, and the phytoplankton under the ice was low in numbers. However, in the spring outside the ice edge, nets clogged under near-bloom conditions, dominated by two gelatinous colony-forming species: the centric diatom Thalassiosira gravida Cleve and the prymnesiophyte Phaeocystis poucheti (Hariot) Lagerheim (Fryxell, Gould, and Watkins 1985). T. gravida was all but lacking in the ice (Buck, Garrison, and Fryxell 1985) and under the ice, but increased greatly outside the ice beyond station 19 (figure 1) at most depths, and it continued to dominate the diatoms in net hauls taken on the Wv Melville away from the ice. It is proposed that Thalassiosira was seeded from the north, perhaps from subsurface layers, and Phaeocystis from the ice-covered waters or the ice itself (Fryxell in preparation.) The pennate diatom genus Nitzschia was also abundant (figure 2), but the great increase in phytoplankton outside the ice can be credited mainly to the centric diatom. Cell ANTARCTIC JOURNAL
