Size fractionation of antarctic phytoplankton
Size fractionation of antarctic phytoplankton S.Z. EL-SAYED and L.H. WEBER Department of Oceanography Texas A&M University College Station, Texas 77843
The antarctic phytoplankton community is generally dominated by organisms less than 20 micrometers in size, as evidenced by size-fractionated measurements of chlorophyll a (Fay 1973; El-Sayed and Taguchi 1981; von Brockel 1981; Yamaguchi and Shibata 1982; Hewes, Holm-Hansen, and Sakshaug 1983; Sasaki 1984; Weber 1984). Attention has been focused recently on the significance of photoautotrophic picoplankton, chlorophyll-containing organisms which are less than 1 to 3 micrometers in size (see Li et al. 1983; Platt, Subba Rao, and Irwin 1983; Takahashi and Bienfang 1983). During two cruises in the 1984 - 1985 austral summer season, we determined the relative contributions of the pico (less than 1 micrometer), nano (greater than 1 micrometer but less than 20 micrometer), and micro (greater than 20 micrometer but less than 200 micrometer) size fractions to the total phytoplankton biomass, as estimated by chlorophyll a. The first cruise was aboard the Federal Republic of Germany's F/s Polarstern in the southwestern Drake Passage and eastern Bransfield Strait (figure 1A) between 14 November and 8 December 1984. The second was aboard the South African Ris Africana in the western Indian sector of the Antarctic (figure 1B) between 20 February and 23 March 1985. Both of these cruises represented the respective country's contributions to phase II of the Second International BIOMASS (Biological Investigation of Marine Antarctic Systems and Stocks) Experiment.
680W K 59°S
As such, multidisciplinary studies revolving around the ecology and physiology of krill were carried out. Our program was designed to assess the vertical and horizontal distribution patterns of phytoplankton biomass, productivity, and species composition in relation to various physico-chemical parameters and to the distribution of krill. Here we report only on the sizefractionated measurements of chlorophyll a. The 33 closely spaced stations occupied in the vicinity of Elephant Island (figure 1A) have an average chlorophyll concentration in the upper water column (down to 100 to 300 meters) of 0.23 milligram per cubic meter, with a maximum of 0.82 milligram per cubic meter. The picoplankton component was not measured at these stations. Overall, the contribution of the less than 20-micrometer size fraction to the total estimated chlorophyll a concentration is 76 percent. The proportion of nanoplankton in surface waters (83 percent) is somewhat higher than for the deepest samples (68 percent). This shift results from a decrease in the concentration of nanoplankton with depth, as the microplankton component is, at all levels, very low (figure 2A). The relative contribtuion of the nanoplankton to total chlorophyll shows station-to-station variability. However, at more than half of the 33 stations, the nanoplankton contributes greater than 85 percent to the surface chlorophyll and greater than 70 percent to water-column mean values of chlorophyll (figure 3A). Average water-column chlorophyll concentrations at the six Polarstern stations outside the Elephant Island grid (stations 200, 201, 203, 206, 207, and 209 in figure 1A) vary greatly, from a low of 0.07 milligram per cubic meter at station 200 to a high of 2.60 milligram per cubic meter at station 207. At these stations, a substantial amount of the chlorophyll is contained in cells which passed through a 1-micrometer Nuclepore filter (figure 2B). The relative contribution of these very small cells to the photoautotrophic biomass varies considerably from station to station, ranging from only 3 percent at station 201 to 70 percent at station 209. (The mean is 40 percent.)
300 E .FRIC5
ELEPHANT I.
600
INDIAN OCE 40°S .200 201 KING GEORGE I.
MARION I. \CROZE
P2O3 B30°
.206
KERGUELEN I.
209
60°
6o
HEARD I.
65 ENDERj LAND
Figure 1. Station positions of the F/S Polarstern (A) and
1985 REVIEW
R/S Africana
60°
(B) cruises.
141
Chlorophyll a (mgm)
Z
0
40 50 60 70 80 90 100
U, Q)
C a)
26
U) C
C) 0
D
U,
9-
0
o2
-C
Z
-J
0 Chlorophyll g (mg-m-3)
25 35 45 55 65 75 85 Chlorophyll (%) in20-pm size fraction
Figure 3. Number of Elephant Island grid stations (A) and Africana stations (B) with various amounts of the mean water column chlorophyll a in the less than 20 micrometer size fraction. ("rim" denotes "micrometer:')
> LQ 0) C
a)
C) C
in
-c -J
Chlorophyll Q (mgm-3)
E -C 0
The 15 Africana stations (figure 1B) have an average chlorophyll concentration in the upper water column (to 150 meters) of 0.29 milligram per cubic meter, with a maximum of 1.48 milligrams per cubic meter. These values are similar to those for the Elephant Island stations. In contrast to the very high proportion of small phytoplankters in the Polarstern samples (and to values generally reported in the literature), the Africana stations display a mean contribution of chlorophyll from cells less than 20 micrometers in size of only 47 percent (range of 29 to 84 percent, figure 3B). Again in marked contrast to the Polarstern samples, the relative contribution of the nanoplankton increases with depth. Cells less than 20 micrometers contribute an average of 37 percent and 62 percent to the total chlorophyll concentration at the surface and 150 meters, respectively. The picoplankton biomass is very low, contributing an average of only 14 percent (range 7 to 43 percent) to the total concentration of chlorophyll. The fact that we found high, but extremely variable, amounts of picoplankton and nanoplankton emphasizes the need to further study the size distribution of antarctic marine phytoplankton. We are grateful to our colleagues of the Alfred-Wegener Institut fur Polarforschung, Bremerhaven, Federal Republic of Germany, and the Sea Fisheries Research Institute, Cape Town, South Africa, for the opportunity to participate with them in the cruises of the F/S Polarstern and R/S Africana. The research re ported herein was supported mostly by personal funds. Grateful acknowledgement is expressed to Kenneth Sherman, Director, Northeast Fisheries Center, National Marine Fisheries Service, for arranging financial assistance through the Fisheries Center. References
Figure 2. Mean vertical distribution of pico 0, nano 0, and net El size fractions of chlorophyll a for the Elephant Island grid stations (A); the other six Polarstern stations (B); and the 15 Afrlcana stations (C). ("mg. m -3" denotes "milligrams per cubic meter.")
142
Brockel, K. von. 1981. The importance of nanoplankton within the pelagic Antarctic ecosystem. Kieler Meeresforschungen Sondcrheft, 5,
61-67. ANTARCTIC JOURNAL
El-Sayed, S.Z., and S. Taguchi. 1981. Primary production and standing crop of phytoplankton along the ice-edge in the Weddell Sea. DeepSea Research, 28A, 1017 - 1032. Fay, R. 1973. Significance of nanoplankton in primary production of the Ross Sea, Antarctica, during the 1972 austral summer. (Doctoral dissertation, Texas A&M University.) Hewes, C.D., 0. Holm-Hansen, and E. Sakshaug. 1983. Nanoplankton and microplankton studies during the circumnavigation cruise. Antarctic Journal of the U.S., 18(5), 169 - 171. Li, W.K.W., D.V. Subba Rao, W.G. Harrison, J.C. Smith, J.J. Cullen, B. Irwin, and T. Platt. 1983. Autotrophic picoplankton in the tropical ocean. Science, 219, 292 - 295. Platt, T., D.V. Subba Rao, and B. Irwin. 1983. Photosynthesis of
picoplankton in the oligotrophic ocean. Nature, 300(5902), 702 - 704. Sasaki, H. 1984. Distribution of nano- and microplankton in the Indian
Phytoplankton from the southwestern Atlantic Ocean
contrary, often the numbers of Phaeocystis and diatoms (from discrete samples taken at 7 or 8 depths at each station) showed increases or decreases that were parallel, or directly related. There was an exception deep under the ice at the southernmost station and in an ice core, where the Phaeocystis maximum was in dim light, but diatoms were not abundant. We have no data on species succession at any one station or in any one water mass as yet. We noted what may have been zygote production by Phaeocystis, with the maximum number of such cells at the surface farthest south into the ice zone (Westwind stations 15, 14) and deeper into the water column north toward the ice edge. This stage will be sought in future collections. Under the ice, the classic antarctic phytoplankton was present, but with few resting spores (Fryxell, Theriot, and Buck 1984). The quantitative analysis showed dominance by species of the diatom genus Nitzschia united in ribbon colonies (figure 2). N,tzschia spp. from the water columns of the two stations farthest south (Westwind stations 15, 14) averaged 70 percent of the diatoms, while those from the stations out of the ice (Westwind stations 20 through 23) averaged less than half that. Absolute numbers of Nitzschia did not decrease, but other diatom numbers showed greater increases. Cell counts of water columns under the ice averaged 22.5 x 10911cells per square meter, an order of magnitude higher than in the open ocean of lower latitudes (Fryxell, Taguchi, and El-Sayed, 1979). Away from the ice edge, cell counts were even higher, with an average of 41.6 x 10 9 cells per square meter in the water columns of the four open-ocean samples of the Westwind. In addition to Phaeocystis, the water column was dominated by Thalassiosira gravida (figure 3). The diatom, like Phaeocystis, occurred in this area in gelatinous colonies. The fact that both dominant taxa, not representing closely related organisms, showed the same growth habit provides enticing clues as to form and function of phytoplankton as well as to the nature of winter water or turbulent water as a medium for phytoplankton growth. T gravida also dominated the net hauls from the R/V Melville, especially in stations farthest north in the early part of the study period, reaching south toward the ice by the first of December.
G.A. FRYXELL, R.W. GOULD, JR., and T.P. WATKINS Department of Oceanography Texas A&M University College Station, Texas 77843
Dynamic changes of phytoplankton abundance under frontal conditions presented by the antarctic ice edge have been confirmed by quantitative data from preserved water samples, relative abundance measurements from net hauls, and experiments with living cultures. Materials were collected on the November and December 1983 cruises of the U.S. Coast Guard icebreaker Westwind and RIV Melville as part of the AMERIEZ (Antarctic Marine Ecosystem Research at the Ice-Edge Zone) project. Our data show an ice-edge phytoplankton increase (not a surface discoloration or "bloom"), dominated by the prymnesiophyte, Phaeocystis poucheti (Hariot) Lagerheim, and the diatom, thalassiosira gravida Cleve. Using samples taken under and in the ice, plus those from the open ocean, we conclude that T. ravi'da was part of austral spring phytoplankton increase inocuated from the west or from the north and travelling south to the ^ ce edge, while Phaeocystis was an important part of phyoplankton under the ice and showed a great increase in situ as he seasonal ice melted (figure 1). Acrylic acid production by Phaeocystis was confirmed by uillard and Hellebust (1971), and it has been suggested that erring avoid dense blooms of this taxon. The colonial stage of Phaeocystis is reputed to affect phytoplankton adversely, as well, t least in northern waters (Yentsch personal communication). I fact, the presence of Phaeocystis can be indicated by an altered ppearance of cellular contents in other phytoplankton (chlor sis and a heavy granulation of the cellular contents, Smayda 1973). Such a negative relationship between the dominant dioms and Phaeocystis was not noted in our material. On the 1 85 REVIEW
sector of the Southern Ocean. Memoirs of National Institute of Polar
Research, (Special Issue No. 32), 38 - 50. Takahashi, M., and P.K. Bienfang. 1983. Size structure of phytoplankton biomass and photosynthesis in subtropical Hawaiian waters. Marine Biology, 76, 203 - 211.
Weber, L.H. 1984. Spatial variability of phytoplankton in relation to the distributional patterns of krill (Euphausia superba). (Doctoral dissertation, Texas A&M University.) Yamaguchi, Y., and Y. Shibata. 1982. Standing stock and distribution of phytoplankton chlorophyll in the Southern Ocean south of Australia. Transactions of Tokyo University Fisheries, 5, 111 - 128.
143
The antarctic phytoplankton community is generally dominated by organisms less than 20 micrometers in size, as evidenced by size-fractionated measurements of chlorophyll a (Fay 1973; El-Sayed and Taguchi 1981; von Brockel 1981; Yamaguchi and Shibata 1982; Hewes, Holm-Hansen, and Sakshaug 1983; Sasaki 1984; Weber 1984). Attention has been focused recently on the significance of photoautotrophic picoplankton, chlorophyll-containing organisms which are less than 1 to 3 micrometers in size (see Li et al. 1983; Platt, Subba Rao, and Irwin 1983; Takahashi and Bienfang 1983). During two cruises in the 1984 - 1985 austral summer season, we determined the relative contributions of the pico (less than 1 micrometer), nano (greater than 1 micrometer but less than 20 micrometer), and micro (greater than 20 micrometer but less than 200 micrometer) size fractions to the total phytoplankton biomass, as estimated by chlorophyll a. The first cruise was aboard the Federal Republic of Germany's F/s Polarstern in the southwestern Drake Passage and eastern Bransfield Strait (figure 1A) between 14 November and 8 December 1984. The second was aboard the South African Ris Africana in the western Indian sector of the Antarctic (figure 1B) between 20 February and 23 March 1985. Both of these cruises represented the respective country's contributions to phase II of the Second International BIOMASS (Biological Investigation of Marine Antarctic Systems and Stocks) Experiment.
680W K 59°S
As such, multidisciplinary studies revolving around the ecology and physiology of krill were carried out. Our program was designed to assess the vertical and horizontal distribution patterns of phytoplankton biomass, productivity, and species composition in relation to various physico-chemical parameters and to the distribution of krill. Here we report only on the sizefractionated measurements of chlorophyll a. The 33 closely spaced stations occupied in the vicinity of Elephant Island (figure 1A) have an average chlorophyll concentration in the upper water column (down to 100 to 300 meters) of 0.23 milligram per cubic meter, with a maximum of 0.82 milligram per cubic meter. The picoplankton component was not measured at these stations. Overall, the contribution of the less than 20-micrometer size fraction to the total estimated chlorophyll a concentration is 76 percent. The proportion of nanoplankton in surface waters (83 percent) is somewhat higher than for the deepest samples (68 percent). This shift results from a decrease in the concentration of nanoplankton with depth, as the microplankton component is, at all levels, very low (figure 2A). The relative contribtuion of the nanoplankton to total chlorophyll shows station-to-station variability. However, at more than half of the 33 stations, the nanoplankton contributes greater than 85 percent to the surface chlorophyll and greater than 70 percent to water-column mean values of chlorophyll (figure 3A). Average water-column chlorophyll concentrations at the six Polarstern stations outside the Elephant Island grid (stations 200, 201, 203, 206, 207, and 209 in figure 1A) vary greatly, from a low of 0.07 milligram per cubic meter at station 200 to a high of 2.60 milligram per cubic meter at station 207. At these stations, a substantial amount of the chlorophyll is contained in cells which passed through a 1-micrometer Nuclepore filter (figure 2B). The relative contribution of these very small cells to the photoautotrophic biomass varies considerably from station to station, ranging from only 3 percent at station 201 to 70 percent at station 209. (The mean is 40 percent.)
300 E .FRIC5
ELEPHANT I.
600
INDIAN OCE 40°S .200 201 KING GEORGE I.
MARION I. \CROZE
P2O3 B30°
.206
KERGUELEN I.
209
60°
6o
HEARD I.
65 ENDERj LAND
Figure 1. Station positions of the F/S Polarstern (A) and
1985 REVIEW
R/S Africana
60°
(B) cruises.
141
Chlorophyll a (mgm)
Z
0
40 50 60 70 80 90 100
U, Q)
C a)
26
U) C
C) 0
D
U,
9-
0
o2
-C
Z
-J
0 Chlorophyll g (mg-m-3)
25 35 45 55 65 75 85 Chlorophyll (%) in20-pm size fraction
Figure 3. Number of Elephant Island grid stations (A) and Africana stations (B) with various amounts of the mean water column chlorophyll a in the less than 20 micrometer size fraction. ("rim" denotes "micrometer:')
> LQ 0) C
a)
C) C
in
-c -J
Chlorophyll Q (mgm-3)
E -C 0
The 15 Africana stations (figure 1B) have an average chlorophyll concentration in the upper water column (to 150 meters) of 0.29 milligram per cubic meter, with a maximum of 1.48 milligrams per cubic meter. These values are similar to those for the Elephant Island stations. In contrast to the very high proportion of small phytoplankters in the Polarstern samples (and to values generally reported in the literature), the Africana stations display a mean contribution of chlorophyll from cells less than 20 micrometers in size of only 47 percent (range of 29 to 84 percent, figure 3B). Again in marked contrast to the Polarstern samples, the relative contribution of the nanoplankton increases with depth. Cells less than 20 micrometers contribute an average of 37 percent and 62 percent to the total chlorophyll concentration at the surface and 150 meters, respectively. The picoplankton biomass is very low, contributing an average of only 14 percent (range 7 to 43 percent) to the total concentration of chlorophyll. The fact that we found high, but extremely variable, amounts of picoplankton and nanoplankton emphasizes the need to further study the size distribution of antarctic marine phytoplankton. We are grateful to our colleagues of the Alfred-Wegener Institut fur Polarforschung, Bremerhaven, Federal Republic of Germany, and the Sea Fisheries Research Institute, Cape Town, South Africa, for the opportunity to participate with them in the cruises of the F/S Polarstern and R/S Africana. The research re ported herein was supported mostly by personal funds. Grateful acknowledgement is expressed to Kenneth Sherman, Director, Northeast Fisheries Center, National Marine Fisheries Service, for arranging financial assistance through the Fisheries Center. References
Figure 2. Mean vertical distribution of pico 0, nano 0, and net El size fractions of chlorophyll a for the Elephant Island grid stations (A); the other six Polarstern stations (B); and the 15 Afrlcana stations (C). ("mg. m -3" denotes "milligrams per cubic meter.")
142
Brockel, K. von. 1981. The importance of nanoplankton within the pelagic Antarctic ecosystem. Kieler Meeresforschungen Sondcrheft, 5,
61-67. ANTARCTIC JOURNAL
El-Sayed, S.Z., and S. Taguchi. 1981. Primary production and standing crop of phytoplankton along the ice-edge in the Weddell Sea. DeepSea Research, 28A, 1017 - 1032. Fay, R. 1973. Significance of nanoplankton in primary production of the Ross Sea, Antarctica, during the 1972 austral summer. (Doctoral dissertation, Texas A&M University.) Hewes, C.D., 0. Holm-Hansen, and E. Sakshaug. 1983. Nanoplankton and microplankton studies during the circumnavigation cruise. Antarctic Journal of the U.S., 18(5), 169 - 171. Li, W.K.W., D.V. Subba Rao, W.G. Harrison, J.C. Smith, J.J. Cullen, B. Irwin, and T. Platt. 1983. Autotrophic picoplankton in the tropical ocean. Science, 219, 292 - 295. Platt, T., D.V. Subba Rao, and B. Irwin. 1983. Photosynthesis of
picoplankton in the oligotrophic ocean. Nature, 300(5902), 702 - 704. Sasaki, H. 1984. Distribution of nano- and microplankton in the Indian
Phytoplankton from the southwestern Atlantic Ocean
contrary, often the numbers of Phaeocystis and diatoms (from discrete samples taken at 7 or 8 depths at each station) showed increases or decreases that were parallel, or directly related. There was an exception deep under the ice at the southernmost station and in an ice core, where the Phaeocystis maximum was in dim light, but diatoms were not abundant. We have no data on species succession at any one station or in any one water mass as yet. We noted what may have been zygote production by Phaeocystis, with the maximum number of such cells at the surface farthest south into the ice zone (Westwind stations 15, 14) and deeper into the water column north toward the ice edge. This stage will be sought in future collections. Under the ice, the classic antarctic phytoplankton was present, but with few resting spores (Fryxell, Theriot, and Buck 1984). The quantitative analysis showed dominance by species of the diatom genus Nitzschia united in ribbon colonies (figure 2). N,tzschia spp. from the water columns of the two stations farthest south (Westwind stations 15, 14) averaged 70 percent of the diatoms, while those from the stations out of the ice (Westwind stations 20 through 23) averaged less than half that. Absolute numbers of Nitzschia did not decrease, but other diatom numbers showed greater increases. Cell counts of water columns under the ice averaged 22.5 x 10911cells per square meter, an order of magnitude higher than in the open ocean of lower latitudes (Fryxell, Taguchi, and El-Sayed, 1979). Away from the ice edge, cell counts were even higher, with an average of 41.6 x 10 9 cells per square meter in the water columns of the four open-ocean samples of the Westwind. In addition to Phaeocystis, the water column was dominated by Thalassiosira gravida (figure 3). The diatom, like Phaeocystis, occurred in this area in gelatinous colonies. The fact that both dominant taxa, not representing closely related organisms, showed the same growth habit provides enticing clues as to form and function of phytoplankton as well as to the nature of winter water or turbulent water as a medium for phytoplankton growth. T gravida also dominated the net hauls from the R/V Melville, especially in stations farthest north in the early part of the study period, reaching south toward the ice by the first of December.
G.A. FRYXELL, R.W. GOULD, JR., and T.P. WATKINS Department of Oceanography Texas A&M University College Station, Texas 77843
Dynamic changes of phytoplankton abundance under frontal conditions presented by the antarctic ice edge have been confirmed by quantitative data from preserved water samples, relative abundance measurements from net hauls, and experiments with living cultures. Materials were collected on the November and December 1983 cruises of the U.S. Coast Guard icebreaker Westwind and RIV Melville as part of the AMERIEZ (Antarctic Marine Ecosystem Research at the Ice-Edge Zone) project. Our data show an ice-edge phytoplankton increase (not a surface discoloration or "bloom"), dominated by the prymnesiophyte, Phaeocystis poucheti (Hariot) Lagerheim, and the diatom, thalassiosira gravida Cleve. Using samples taken under and in the ice, plus those from the open ocean, we conclude that T. ravi'da was part of austral spring phytoplankton increase inocuated from the west or from the north and travelling south to the ^ ce edge, while Phaeocystis was an important part of phyoplankton under the ice and showed a great increase in situ as he seasonal ice melted (figure 1). Acrylic acid production by Phaeocystis was confirmed by uillard and Hellebust (1971), and it has been suggested that erring avoid dense blooms of this taxon. The colonial stage of Phaeocystis is reputed to affect phytoplankton adversely, as well, t least in northern waters (Yentsch personal communication). I fact, the presence of Phaeocystis can be indicated by an altered ppearance of cellular contents in other phytoplankton (chlor sis and a heavy granulation of the cellular contents, Smayda 1973). Such a negative relationship between the dominant dioms and Phaeocystis was not noted in our material. On the 1 85 REVIEW
sector of the Southern Ocean. Memoirs of National Institute of Polar
Research, (Special Issue No. 32), 38 - 50. Takahashi, M., and P.K. Bienfang. 1983. Size structure of phytoplankton biomass and photosynthesis in subtropical Hawaiian waters. Marine Biology, 76, 203 - 211.
Weber, L.H. 1984. Spatial variability of phytoplankton in relation to the distributional patterns of krill (Euphausia superba). (Doctoral dissertation, Texas A&M University.) Yamaguchi, Y., and Y. Shibata. 1982. Standing stock and distribution of phytoplankton chlorophyll in the Southern Ocean south of Australia. Transactions of Tokyo University Fisheries, 5, 111 - 128.
143
