Photoadaptation in sea-ice microalgae in McMurdo Sound
R.R. Siegfrieg (Ed.), Fourth symposium on antarctic biology: Nutrient cycles and food chains.
Steemann Nielsen, E. 1962. On the maximum quantity of plankton chlorophyll per surface unit of a lake or the sea. Internationale revue der gesamten Hydrobiologie, 43, 330-338. Sullivan, C.W., and A.C. Palmisano. 1984. Sea ice microbial communities: Distribution, abundance, and diversity of ice bacteria in
Photoadaptation in sea-ice microalgae in McMurdo Sound A. C. PALMISANO, J. B. SooHoo, and C. W. SULLIVAN
Allan Hancock Foundation and Department of Biological Sciences University of Southern California Los Angeles, California 90089
Microalgae living in the bottom of annual sea ice in McMurdo Sound, Antarctica are uniquely adapted to ambient low-light conditions. Irradiance beneath annual sea ice is typically less than 1 percent of surface downwelling irradiance; light is attenuated when it passes through surface snow, 2 to 3 meters of sea ice, and the algal layer. Despite irradiances often less than 15 microEinsteins per square meter per second, standing crops as high as 300 milligrams of chlorophyll a per square meter have been reported for sea-ice microalgae in McMurdo Sound (Palmisano and Sullivan 1983). Over two decades ago, Bunt (1964) suggested that sea-ice microalgae are "shade" adapted; since then, however, this problem has received little attention. In the austral spring of 1983, we began a study of photoadap tation in sea-ice microalgae. Our study site was offshore of Cape Armitage where annual sea ice was 230 centimeters thick. Samples were collected from the bottom of hard congelation ice using a SIPRE ice auger and from the unconsolidated ice-platelet layer by scuba divers. The mean standing crop of sea-ice microalgae at our study site was 169 milligrams of chlorophyll a per square meter. Carbon-to-nitrogen ratios averaged 7.5. Phaeopigments in Cape Armitage sea ice were low, with phaeopigment-to-chiorophyll ratios consistently below 0.1. We studied the relationship between photosynthesis and irradiance over a range of 0-300 microEinsteins per square meter per second. Photosynthetic rate was estimated by the uptake of NaH 14 CO 3 at - 2°C, the ambient water temperature in McMurdo Sound. We fit the data to the empirically derived equations of Platt, Gallegos, and Harrison (1980) which describe photosynthesis as a continuous function of light. A photosynthesis/irradiance curve for sea-ice microalgae from Cape Armitage congelation ice collected on 1 December 1983 is shown in the figure. A maximum photosynthetic rate (P max) of 0.06 milligrams of carbon per milligram of chlorophyll a per hour was reached at 5 microEinsteins per square meter per second. This P max is significantly lower than those for temperate phytoplankton whose P max rates usually range from 2-10 1984 REVIEW
McMurdo Sound, Antarctica, in 1980. Applied and Environmental Microbiology, 47(4), 788-795. Sullivan, C.W., A.C. Palmisano, S. Kottmeier, S. McGrath-Grossi, and R. Moe. 1983. The influence of light on growth and development of the sea-ice microbial community in McMurdo Sound. In: R.R. Siegfrieg (Ed.), Fourth symposium on antarctic biology: Nutrient cycles and food chains.
milligrams of carbon per milligram of chlorophyll a per hour (Falkowski 1981). Photosynthesis was inhibited at irradiances greater than 60 microEinsteins per square meter per second. Our data demonstrate the extremely shade-adapted nature of photosynthesis in ice microalgae. We are currently using sea-ice microalgae as a model to study the rate of photoadaptation to altered light fields. By manipulating light available to sea-ice algae using snow cover, we followed shifts in photosynthetic parameters in algal cells exposed to higher or lower irradiance. Moreover, shifts in in vivo absorption and fluorescence excitation spectra were evident in sea-ice microalgae at reduced irradiances. These results may indicate changes in photosystems or an increasing role of accessory pigments in light harvesting and energy transfer (SooHoo et al. in preparation). We also obtained evidence that the end products of photosynthesis vary considerably between congelation and platelet ice communities. We thank Ann Muscat, Jon Kastendiek, Lin Craft, and John Wood for diving support and Steve Kottmeier and Glen Smith for field assistance. This research was supported by National Science Foundation grant DPP 83-04985.
Photosynthesis-irradiance relationship In sea-ice microalgae collected from the bottom of congelation ice at Cape Armitage. ("MG C/ MG CHL A/HR" denotes milligrams of carbon per milligram of chlorophyll a per hour; "pEIM2ISEC" denotes microEinsteins per square meter per second.)
131
References Bunt, 1.5. 1964. Primary production under sea ice in Antarctic waters. 2. Influence of light and other factors on photosynthetic activities of Antarctic marine microalgae. Antarctic Research Series, 1, 27. Falkowski, P.C. 1981. Light-shade adaptation and assimilation numbers. Journal of Plankton Research, 3, 203. Palmisano, A.C., and C.W. Sullivan. 1983. Sea ice microbial communities. 1. Distribution, abundance, and primary production of ice
microalgae in McMurdo Sound, Antarctica in 1980. Polar Biology, 2, 171. Platt, T., C.L. Gallegos, and W.G. Harrison. 1980. Photoinhibition of photosynthesis in natural assemblages of marine phytoplankton. Journal of Marine Research, 38, 687. SooHoo, J. Beeler, D.A. Kiefer, D.J. Collins, and I.S. McDermid. In preparation. In vivo fluorescence excitation and absorption spectra of marine phytoplankton: Responses to photoadaptation.
Species-specific productivity in an iceedge phytoplankton bloom in the Ross Sea
tion of individual species to the overall production of the bloom. This procedure allowed us to assess the productivity of each species encountered so we could determine if epontic species were physiologically active upon release into the water column. Between 26 January and 2 February 1983, 36 hydrographic stations were occupied along three transects situated perpendicular to the receding ice edge (figure). Those stations closest to shore (e.g., station 36) were in 100 percent ice cover while those most seaward (e.g., stations 41-43) were in open water. Two transects can be defined by stations at which speciesspecific productivity was measured: transect 1: stations 2, 3, 4, 5, 11; and transect 2: stations 34, 35, 32, 29, 27. At each station along these two transects water samples were collected from the depths of 100-, 30-, and 5-percent light penetration and were used to measure standing stock and relative abundance of species present as well as for autoradiographic analysis. Autoradiography was completed using the methods of Paerl and Goldman (1972). Routine primary productivity was measured from water samples collected at seven depths at each of the hydrographic stations. The study area was characterized by elevated levels of primary production and phytoplankton biomass which extended some 250 kilometers seaward of the ice edge. The mean surface and integrated euphotic productivity within the study area were 2.39 ± 1.12 milligrams of carbon per cubic meter per hour and 936.5 ± 497.1 milligrams of carbon per square meter per
D. L. WILSON and W. 0. SMITH Department of Botany University of Tennessee Knoxville, Tennessee 37996
Recent studies have shown the importance of phytoplankton blooms in marginal ice zones (e.g., El-Sayed and Taguchi 1981), yet little is known concerning the duration, extent, or control mechanisms of such blooms. During January and February 1983, we conducted a study of the ice-edge phytoplankton bloom in the Ross Sea. The purpose of this study was to determine the level and nature of phytoplankton production within the bloom and to assess the relationship between the spatial and temporal distribution of this production and the physical and chemical characteristics of the water column. As part of this project, grain-density autoradiography, coupled with quantitative cell counts, was used to determine the relative contribu-
Study area. Stations represented by squares indicate stations at which autoradiography was performed. 132
ANTARCTIC JOURNAL
Steemann Nielsen, E. 1962. On the maximum quantity of plankton chlorophyll per surface unit of a lake or the sea. Internationale revue der gesamten Hydrobiologie, 43, 330-338. Sullivan, C.W., and A.C. Palmisano. 1984. Sea ice microbial communities: Distribution, abundance, and diversity of ice bacteria in
Photoadaptation in sea-ice microalgae in McMurdo Sound A. C. PALMISANO, J. B. SooHoo, and C. W. SULLIVAN
Allan Hancock Foundation and Department of Biological Sciences University of Southern California Los Angeles, California 90089
Microalgae living in the bottom of annual sea ice in McMurdo Sound, Antarctica are uniquely adapted to ambient low-light conditions. Irradiance beneath annual sea ice is typically less than 1 percent of surface downwelling irradiance; light is attenuated when it passes through surface snow, 2 to 3 meters of sea ice, and the algal layer. Despite irradiances often less than 15 microEinsteins per square meter per second, standing crops as high as 300 milligrams of chlorophyll a per square meter have been reported for sea-ice microalgae in McMurdo Sound (Palmisano and Sullivan 1983). Over two decades ago, Bunt (1964) suggested that sea-ice microalgae are "shade" adapted; since then, however, this problem has received little attention. In the austral spring of 1983, we began a study of photoadap tation in sea-ice microalgae. Our study site was offshore of Cape Armitage where annual sea ice was 230 centimeters thick. Samples were collected from the bottom of hard congelation ice using a SIPRE ice auger and from the unconsolidated ice-platelet layer by scuba divers. The mean standing crop of sea-ice microalgae at our study site was 169 milligrams of chlorophyll a per square meter. Carbon-to-nitrogen ratios averaged 7.5. Phaeopigments in Cape Armitage sea ice were low, with phaeopigment-to-chiorophyll ratios consistently below 0.1. We studied the relationship between photosynthesis and irradiance over a range of 0-300 microEinsteins per square meter per second. Photosynthetic rate was estimated by the uptake of NaH 14 CO 3 at - 2°C, the ambient water temperature in McMurdo Sound. We fit the data to the empirically derived equations of Platt, Gallegos, and Harrison (1980) which describe photosynthesis as a continuous function of light. A photosynthesis/irradiance curve for sea-ice microalgae from Cape Armitage congelation ice collected on 1 December 1983 is shown in the figure. A maximum photosynthetic rate (P max) of 0.06 milligrams of carbon per milligram of chlorophyll a per hour was reached at 5 microEinsteins per square meter per second. This P max is significantly lower than those for temperate phytoplankton whose P max rates usually range from 2-10 1984 REVIEW
McMurdo Sound, Antarctica, in 1980. Applied and Environmental Microbiology, 47(4), 788-795. Sullivan, C.W., A.C. Palmisano, S. Kottmeier, S. McGrath-Grossi, and R. Moe. 1983. The influence of light on growth and development of the sea-ice microbial community in McMurdo Sound. In: R.R. Siegfrieg (Ed.), Fourth symposium on antarctic biology: Nutrient cycles and food chains.
milligrams of carbon per milligram of chlorophyll a per hour (Falkowski 1981). Photosynthesis was inhibited at irradiances greater than 60 microEinsteins per square meter per second. Our data demonstrate the extremely shade-adapted nature of photosynthesis in ice microalgae. We are currently using sea-ice microalgae as a model to study the rate of photoadaptation to altered light fields. By manipulating light available to sea-ice algae using snow cover, we followed shifts in photosynthetic parameters in algal cells exposed to higher or lower irradiance. Moreover, shifts in in vivo absorption and fluorescence excitation spectra were evident in sea-ice microalgae at reduced irradiances. These results may indicate changes in photosystems or an increasing role of accessory pigments in light harvesting and energy transfer (SooHoo et al. in preparation). We also obtained evidence that the end products of photosynthesis vary considerably between congelation and platelet ice communities. We thank Ann Muscat, Jon Kastendiek, Lin Craft, and John Wood for diving support and Steve Kottmeier and Glen Smith for field assistance. This research was supported by National Science Foundation grant DPP 83-04985.
Photosynthesis-irradiance relationship In sea-ice microalgae collected from the bottom of congelation ice at Cape Armitage. ("MG C/ MG CHL A/HR" denotes milligrams of carbon per milligram of chlorophyll a per hour; "pEIM2ISEC" denotes microEinsteins per square meter per second.)
131
References Bunt, 1.5. 1964. Primary production under sea ice in Antarctic waters. 2. Influence of light and other factors on photosynthetic activities of Antarctic marine microalgae. Antarctic Research Series, 1, 27. Falkowski, P.C. 1981. Light-shade adaptation and assimilation numbers. Journal of Plankton Research, 3, 203. Palmisano, A.C., and C.W. Sullivan. 1983. Sea ice microbial communities. 1. Distribution, abundance, and primary production of ice
microalgae in McMurdo Sound, Antarctica in 1980. Polar Biology, 2, 171. Platt, T., C.L. Gallegos, and W.G. Harrison. 1980. Photoinhibition of photosynthesis in natural assemblages of marine phytoplankton. Journal of Marine Research, 38, 687. SooHoo, J. Beeler, D.A. Kiefer, D.J. Collins, and I.S. McDermid. In preparation. In vivo fluorescence excitation and absorption spectra of marine phytoplankton: Responses to photoadaptation.
Species-specific productivity in an iceedge phytoplankton bloom in the Ross Sea
tion of individual species to the overall production of the bloom. This procedure allowed us to assess the productivity of each species encountered so we could determine if epontic species were physiologically active upon release into the water column. Between 26 January and 2 February 1983, 36 hydrographic stations were occupied along three transects situated perpendicular to the receding ice edge (figure). Those stations closest to shore (e.g., station 36) were in 100 percent ice cover while those most seaward (e.g., stations 41-43) were in open water. Two transects can be defined by stations at which speciesspecific productivity was measured: transect 1: stations 2, 3, 4, 5, 11; and transect 2: stations 34, 35, 32, 29, 27. At each station along these two transects water samples were collected from the depths of 100-, 30-, and 5-percent light penetration and were used to measure standing stock and relative abundance of species present as well as for autoradiographic analysis. Autoradiography was completed using the methods of Paerl and Goldman (1972). Routine primary productivity was measured from water samples collected at seven depths at each of the hydrographic stations. The study area was characterized by elevated levels of primary production and phytoplankton biomass which extended some 250 kilometers seaward of the ice edge. The mean surface and integrated euphotic productivity within the study area were 2.39 ± 1.12 milligrams of carbon per cubic meter per hour and 936.5 ± 497.1 milligrams of carbon per square meter per
D. L. WILSON and W. 0. SMITH Department of Botany University of Tennessee Knoxville, Tennessee 37996
Recent studies have shown the importance of phytoplankton blooms in marginal ice zones (e.g., El-Sayed and Taguchi 1981), yet little is known concerning the duration, extent, or control mechanisms of such blooms. During January and February 1983, we conducted a study of the ice-edge phytoplankton bloom in the Ross Sea. The purpose of this study was to determine the level and nature of phytoplankton production within the bloom and to assess the relationship between the spatial and temporal distribution of this production and the physical and chemical characteristics of the water column. As part of this project, grain-density autoradiography, coupled with quantitative cell counts, was used to determine the relative contribu-
Study area. Stations represented by squares indicate stations at which autoradiography was performed. 132
ANTARCTIC JOURNAL
