RACER: Dynamics of the Antarctic Peninsula coastal ecosystemâ An ...
Fevolden, S. E., and R. Y. George. 1984. Size frequency pattern of Euphausia superha in the Antarctic peninsula waters in the austral summer of 1983. Journal of Crustacean Biology, (special number) 4, 107-122. Holm-Hansen, 0., R. Letelier, and B.G. Mitchell. 1987. RACER: Temporal and spatial distribution of phytoplankton biomass and primary production. Antarctic Journal of the U.S., 22(5). Huntley, M. E., and E. Brinton. 1987. RACER: Mesoscale variation in the growth and early development of Euphausia superba Dana. Antarctic Journal of the U.S., 22(5). Huntley, M.E., D.M. Karl, P. Niiler, and 0. Holm-Hansen. 1987. RACER: An interdisciplinary field study. Antarctic Journal of the U.S., 22(5).
Kitte!, W. 1980. Populational studies on Euphausia superba Dana, 1852 (Euphausiacea, Crustacea) in waters of the Admiralty Bay during Antarctic summer of 1978. Polish Archives of Hydrobiology, 27, 267-272. Marr, J.W.S. 1962. The natural history and geography of the Antarctic krill (Euphausia superha Dana). Discovery Reports, 32, 33-464. Quetin, L.B., and R.M. Ross. 1984. School composition of the antarctic krill Euphausia superba in the waters west of the Antarctic Peninsula in the austral summer of 1982. Journal of Crustacean Biology, (special number) 4, 96-106. Siegel, V. 1986. Investigation of the biology of the antarctic krill Euphausia superba, in the region of the Bransfield Strait and adjacent area. Hamburg: Mitteilungen aus dem Institut für Seefischerei.
RACER: Dynamics of the Antarctic Peninsula coastal ecosystem— An overview
were greater—by more than one order of magnitude—in waters of the Gerlache Strait and north of Brabant Island than in waters of the southern Drake Passage (Holm-Hansen, Letelier and Mitchell; Bailiff et al.; Haberstroh et al., Antarctic Journal, this issue). Pigment-specific primary production was linearly related to temperature within the ambient range observed (HolmHansen et al., Antarctic Journal, this issue). The ranges in chlorophyll a (0.2-20 micrograms per liter), particulate ATP (18-1,400 nanograms per liter), and primary production (80-3,000 milli grams of carbon per square meter per day) span the full range of these variables previously reported for surface waters of the world ocean. With the decline of the spring phytoplankton bloom, we observed the following significant changes: • nitrate concentrations decreased from more than 25 micromoles to less than 3 micromoles (Karl et al., Antarctic Journal, this issue) • ammonia concentrations increased from undetectable levels to more than 10 micromoles (D. Karl, University of Hawaii, unpublished data); • particulate matter was dominated first by large (more than 20 micrometers) then by smaller (less than 20 micrometers) particles (Tien et al., Antarctic Journal, this issue); • community succession from large diatoms to bacteria and autotrophic nanoplankton, and finally to heterotrophic flagellates (Tien et al., Antarctic Journal, this issue). Downward flux of biogenic carbon lagged the bloom, reaching a maximum in the northern Gerlache Strait of 373 milligrams of carbon per square meter per day in January, and falling to less than 15 milligrams of carbon per square meter per day by late March (Karl et al., Antarctic Journal, this issue). During the early phase of the bloom most carbon production contributed to a net increase in phytoplankton standing stock; vertical flux consisted primarily of living matter. As the bloom declined the downward flux came to be dominated by nonliving matter such as dead algae, detritus, and zooplankton feces (Karl et al., Antarctic Journal, this issue). Among the copepods, Calanoides acutus dominated in December and January and Metridia gerlachei became important in the late summer. Grazing rates of C. acutus were greatest in areas of high phytoplankton biomass and primary production, but their egg production was not related to ambient food conditions (Huntley, Mann, and Oresland, Antarctic Journal, this issue). The first major spawning of Euphausia superha occurred in December, with early larvae appearing in mid-January in the Gerlache Strait and southwestern Bransfield Strait (Huntley
M.E. HUNTLEY, P. NHLER, and 0. HOLM-HANSEN Scripps Institution of Oceanography La Jolla, California 92093
D. M. KARL Department of Oceanography University of Hawaii Honolulu, Hawaii 96822
The Research on Antarctic Coastal Ecosystem Rates (RACER) program has provided one of the most comprehensive studies to date of mesoscale ecosystem dynamics in antarctic coastal waters. The key hypotheses and fundamental sampling strategy are discussed by Huntley etal. (Antarctic Journal, this issue); here we present a summary of our findings in the pilot field year of the program. Amos (Antarctic Journal, this issue) defined seven distinct water masses within the 25,000-square-kilometer study area, some of which were not revealed by previous studies using coarser sampling. A strong northeasterly flow (up to 30 centimeters per second) across the Bransfield Strait, from Brabant to Livingston Island, marks the front between "Bellingshausen" and "Weddell" waters. An unusually warm >2.5°C) zone of surface water which appeared at the northern entrance to Gerlache Strait in December and persisted through January indicates a possible eddy created by the island effect we hypothesized. Biologically productive areas were characterized by high temperatures, steep pycnoclines, a shallow mixed layer (approximately 10 meters) and low penetration of irradiance (Amos; Mitchell, Menzies, and Holm-Hansen, Antarctic Journal, this issue). Beam attenuation and diffuse attenuation coefficients showed that in productive waters, there was often insufficient light for photosynthesis below 15 meters (Mitchell, Menzies, and Holm-Hansen, Antarctic Journal, this issue). The spring phytoplankton bloom was well underway by December and declined in succeeding months. Primary productivity, phytoplankton biomass, bacterial production, and biomass 1987 REVIEW
165
and Brinton, Antarctic Journal, this issue), but we found little evidence of the reproductive adults which should have spawned these larvae in the Gerlache Strait region in December (Brinton, Antarctic Journal, this issue). These first larvae developed, as a traceable and regional cohort, to late furcilia by the end of March. In the northern Gerlache Strait larval E. superba were more abundant, consistently larger, and developed and grew faster than in the Bransfield Strait and Drake Passage (Huntley and Brinton, Antarctic Journal, this issue). Throughout the season, populations of postlarval krill were dominated by juveniles in coastal regions of the Antarctic Peninsula and by reproductive adults in the vicinity of the South Shetland Islands (Brinton, Antarctic Journal, this issue). This latter population spawned in February, producing an abundance of larvae almost equal to that earlier in the season in the Gerlache Strait; however, this second group of larvae was smaller and grew almost one order of magnitude more slowly (Huntley and Brinton, Antarctic Journal, this issue). We believe the Gerlache Strait may be an important nursery ground for krill. Results of the pilot RACER program suggest an hypothesis for the development, maintenance, and regional variation of the spring bloom. Primary production in early spring is greatest in nearshore embayments, which are the first waters to stabilize due to protection from storms and high input of meltwater. Pigments associated with high phytoplankton biomass cause light absorption and heat dissipation near the surface; phytoplankton respond to higher temperatures with increased productivity. Continued stability, productivity, and sedimentation rates eventually reduce nutrient concentrations. High productivity is maintained by nutrients recycled through grazing processes. We believe this process may be inhibited in waters of the Bransfield Strait and Drake Passage due to frequent wind-induced deep mixing. Renewed studies should address this hypothesis in detail. Good relationships now developed between optical characteristics and phytoplankton biomass and primary production (Mitchell et al., Antarctic Journal, this issue) should improve the prospects for successful application of remote sensing technology in this challenging region. It is our pleasure to thank the crew of RIv Polar Duke and support staff at Palmer Station, who greatly aided our field
166
research efforts. This research was supported by National Science Foundation grants DPP 85-17269 (to Huntley and Brinton), DPP 85-18748 (to Karl), and DPP 85-19908 (to Holm-Hansen). References Amos, A.F. 1987. RACER: Physical oceanography of the western Bransfield Strait. Antarctic Journal of the U.S., 22(5). Bailiff, M.D., D. Jones, M. Nawrocki, B. Tilbrook, P. Haberstroh, C. Tien, G.T. Taylor, and D.M. Karl. 1987. RACER: Bacterial abundance and thymidine incorporation in the Brarisfield Strait, 1986-1987. Antarctic Journal of the U.S., 22(5). Brinton, E. 1987. RACER: Population structures of Euphausia superba near the Antarctic Peninsula, December to March 1986-1987. Antarctic Journal of the U.S., 22(5). Haberstroh, P.R., M.D. Bailiff, C. Tier, C.T. Taylor, D. Jones, B. Tilbrook, M. Nawrocki, and D.M. Karl. 1987. RACER: Dissolved free amino acid concentrations, molecular composition, and microbial uptake rates in the Bransfield Strait. Antarctic Journal of the U.S., 22(5). Holm-Hansen, 0., R. Letelier, and B.C. Mitchell. 1987. RACER: Temporal and spatial distribution of phytoplankton biomass and primary production. Antarctic Journal of the U.S.. 22(5). Huntley, M., and E. Brinton. 1987. RACER: Mesoscale variation in the growth and early development of larval Euphausia superba. Antarctic Journal of the U.S., 22(5). Huntley, M., D.M. Karl, P. Niiler and 0. Holm-Hansen. 1987. RACER: An interdisciplinary field study. Antarctic Journal of the U.S., 22(5). Huntley, M., V. Mann, and V. Oresland. 1987. RACER: Feeding and egg production rates of some antarctic copepods. Antarctic Journal of the U. S., 22(5). Karl, D.M., C. Tien, D. Jones, B. Tilbrook, M.D. Bailiff, M. Nawrocki, C. Taylor, and P. Haberstroh. 1987. RACER: Seasonal changes in the downward flux of biogenic matter. Journal of the U.S., 22(5). Mitchell, B.C., D. Menzies and 0. Holm-Hansen. 1987. RACER: op Antarctic Journal of-ticaloengrphyfwstBanieldSr. the U. S., 22(5). Mitchell, B.C., C. Stallings, 0. Holm-Hansen, and D. Kiefer. 1987. RACER: Optical prediction of photobiological properties. Antarctic Journal of the U.S., 22(5). Tien, C., D. Jones, M.D. Bailiff, M. Nawrocki, B. Tilbrook, P. Haberstroh, G.T. Taylor, and D.M. Karl. 1987. RACER: Spatial and temporal variations in microbial biomass. Antarctic Journal of the U.S., 22(5).
ANTARCTIC JOURNAL
Kitte!, W. 1980. Populational studies on Euphausia superba Dana, 1852 (Euphausiacea, Crustacea) in waters of the Admiralty Bay during Antarctic summer of 1978. Polish Archives of Hydrobiology, 27, 267-272. Marr, J.W.S. 1962. The natural history and geography of the Antarctic krill (Euphausia superha Dana). Discovery Reports, 32, 33-464. Quetin, L.B., and R.M. Ross. 1984. School composition of the antarctic krill Euphausia superba in the waters west of the Antarctic Peninsula in the austral summer of 1982. Journal of Crustacean Biology, (special number) 4, 96-106. Siegel, V. 1986. Investigation of the biology of the antarctic krill Euphausia superba, in the region of the Bransfield Strait and adjacent area. Hamburg: Mitteilungen aus dem Institut für Seefischerei.
RACER: Dynamics of the Antarctic Peninsula coastal ecosystem— An overview
were greater—by more than one order of magnitude—in waters of the Gerlache Strait and north of Brabant Island than in waters of the southern Drake Passage (Holm-Hansen, Letelier and Mitchell; Bailiff et al.; Haberstroh et al., Antarctic Journal, this issue). Pigment-specific primary production was linearly related to temperature within the ambient range observed (HolmHansen et al., Antarctic Journal, this issue). The ranges in chlorophyll a (0.2-20 micrograms per liter), particulate ATP (18-1,400 nanograms per liter), and primary production (80-3,000 milli grams of carbon per square meter per day) span the full range of these variables previously reported for surface waters of the world ocean. With the decline of the spring phytoplankton bloom, we observed the following significant changes: • nitrate concentrations decreased from more than 25 micromoles to less than 3 micromoles (Karl et al., Antarctic Journal, this issue) • ammonia concentrations increased from undetectable levels to more than 10 micromoles (D. Karl, University of Hawaii, unpublished data); • particulate matter was dominated first by large (more than 20 micrometers) then by smaller (less than 20 micrometers) particles (Tien et al., Antarctic Journal, this issue); • community succession from large diatoms to bacteria and autotrophic nanoplankton, and finally to heterotrophic flagellates (Tien et al., Antarctic Journal, this issue). Downward flux of biogenic carbon lagged the bloom, reaching a maximum in the northern Gerlache Strait of 373 milligrams of carbon per square meter per day in January, and falling to less than 15 milligrams of carbon per square meter per day by late March (Karl et al., Antarctic Journal, this issue). During the early phase of the bloom most carbon production contributed to a net increase in phytoplankton standing stock; vertical flux consisted primarily of living matter. As the bloom declined the downward flux came to be dominated by nonliving matter such as dead algae, detritus, and zooplankton feces (Karl et al., Antarctic Journal, this issue). Among the copepods, Calanoides acutus dominated in December and January and Metridia gerlachei became important in the late summer. Grazing rates of C. acutus were greatest in areas of high phytoplankton biomass and primary production, but their egg production was not related to ambient food conditions (Huntley, Mann, and Oresland, Antarctic Journal, this issue). The first major spawning of Euphausia superha occurred in December, with early larvae appearing in mid-January in the Gerlache Strait and southwestern Bransfield Strait (Huntley
M.E. HUNTLEY, P. NHLER, and 0. HOLM-HANSEN Scripps Institution of Oceanography La Jolla, California 92093
D. M. KARL Department of Oceanography University of Hawaii Honolulu, Hawaii 96822
The Research on Antarctic Coastal Ecosystem Rates (RACER) program has provided one of the most comprehensive studies to date of mesoscale ecosystem dynamics in antarctic coastal waters. The key hypotheses and fundamental sampling strategy are discussed by Huntley etal. (Antarctic Journal, this issue); here we present a summary of our findings in the pilot field year of the program. Amos (Antarctic Journal, this issue) defined seven distinct water masses within the 25,000-square-kilometer study area, some of which were not revealed by previous studies using coarser sampling. A strong northeasterly flow (up to 30 centimeters per second) across the Bransfield Strait, from Brabant to Livingston Island, marks the front between "Bellingshausen" and "Weddell" waters. An unusually warm >2.5°C) zone of surface water which appeared at the northern entrance to Gerlache Strait in December and persisted through January indicates a possible eddy created by the island effect we hypothesized. Biologically productive areas were characterized by high temperatures, steep pycnoclines, a shallow mixed layer (approximately 10 meters) and low penetration of irradiance (Amos; Mitchell, Menzies, and Holm-Hansen, Antarctic Journal, this issue). Beam attenuation and diffuse attenuation coefficients showed that in productive waters, there was often insufficient light for photosynthesis below 15 meters (Mitchell, Menzies, and Holm-Hansen, Antarctic Journal, this issue). The spring phytoplankton bloom was well underway by December and declined in succeeding months. Primary productivity, phytoplankton biomass, bacterial production, and biomass 1987 REVIEW
165
and Brinton, Antarctic Journal, this issue), but we found little evidence of the reproductive adults which should have spawned these larvae in the Gerlache Strait region in December (Brinton, Antarctic Journal, this issue). These first larvae developed, as a traceable and regional cohort, to late furcilia by the end of March. In the northern Gerlache Strait larval E. superba were more abundant, consistently larger, and developed and grew faster than in the Bransfield Strait and Drake Passage (Huntley and Brinton, Antarctic Journal, this issue). Throughout the season, populations of postlarval krill were dominated by juveniles in coastal regions of the Antarctic Peninsula and by reproductive adults in the vicinity of the South Shetland Islands (Brinton, Antarctic Journal, this issue). This latter population spawned in February, producing an abundance of larvae almost equal to that earlier in the season in the Gerlache Strait; however, this second group of larvae was smaller and grew almost one order of magnitude more slowly (Huntley and Brinton, Antarctic Journal, this issue). We believe the Gerlache Strait may be an important nursery ground for krill. Results of the pilot RACER program suggest an hypothesis for the development, maintenance, and regional variation of the spring bloom. Primary production in early spring is greatest in nearshore embayments, which are the first waters to stabilize due to protection from storms and high input of meltwater. Pigments associated with high phytoplankton biomass cause light absorption and heat dissipation near the surface; phytoplankton respond to higher temperatures with increased productivity. Continued stability, productivity, and sedimentation rates eventually reduce nutrient concentrations. High productivity is maintained by nutrients recycled through grazing processes. We believe this process may be inhibited in waters of the Bransfield Strait and Drake Passage due to frequent wind-induced deep mixing. Renewed studies should address this hypothesis in detail. Good relationships now developed between optical characteristics and phytoplankton biomass and primary production (Mitchell et al., Antarctic Journal, this issue) should improve the prospects for successful application of remote sensing technology in this challenging region. It is our pleasure to thank the crew of RIv Polar Duke and support staff at Palmer Station, who greatly aided our field
166
research efforts. This research was supported by National Science Foundation grants DPP 85-17269 (to Huntley and Brinton), DPP 85-18748 (to Karl), and DPP 85-19908 (to Holm-Hansen). References Amos, A.F. 1987. RACER: Physical oceanography of the western Bransfield Strait. Antarctic Journal of the U.S., 22(5). Bailiff, M.D., D. Jones, M. Nawrocki, B. Tilbrook, P. Haberstroh, C. Tien, G.T. Taylor, and D.M. Karl. 1987. RACER: Bacterial abundance and thymidine incorporation in the Brarisfield Strait, 1986-1987. Antarctic Journal of the U.S., 22(5). Brinton, E. 1987. RACER: Population structures of Euphausia superba near the Antarctic Peninsula, December to March 1986-1987. Antarctic Journal of the U.S., 22(5). Haberstroh, P.R., M.D. Bailiff, C. Tier, C.T. Taylor, D. Jones, B. Tilbrook, M. Nawrocki, and D.M. Karl. 1987. RACER: Dissolved free amino acid concentrations, molecular composition, and microbial uptake rates in the Bransfield Strait. Antarctic Journal of the U.S., 22(5). Holm-Hansen, 0., R. Letelier, and B.C. Mitchell. 1987. RACER: Temporal and spatial distribution of phytoplankton biomass and primary production. Antarctic Journal of the U.S.. 22(5). Huntley, M., and E. Brinton. 1987. RACER: Mesoscale variation in the growth and early development of larval Euphausia superba. Antarctic Journal of the U.S., 22(5). Huntley, M., D.M. Karl, P. Niiler and 0. Holm-Hansen. 1987. RACER: An interdisciplinary field study. Antarctic Journal of the U.S., 22(5). Huntley, M., V. Mann, and V. Oresland. 1987. RACER: Feeding and egg production rates of some antarctic copepods. Antarctic Journal of the U. S., 22(5). Karl, D.M., C. Tien, D. Jones, B. Tilbrook, M.D. Bailiff, M. Nawrocki, C. Taylor, and P. Haberstroh. 1987. RACER: Seasonal changes in the downward flux of biogenic matter. Journal of the U.S., 22(5). Mitchell, B.C., D. Menzies and 0. Holm-Hansen. 1987. RACER: op Antarctic Journal of-ticaloengrphyfwstBanieldSr. the U. S., 22(5). Mitchell, B.C., C. Stallings, 0. Holm-Hansen, and D. Kiefer. 1987. RACER: Optical prediction of photobiological properties. Antarctic Journal of the U.S., 22(5). Tien, C., D. Jones, M.D. Bailiff, M. Nawrocki, B. Tilbrook, P. Haberstroh, G.T. Taylor, and D.M. Karl. 1987. RACER: Spatial and temporal variations in microbial biomass. Antarctic Journal of the U.S., 22(5).
ANTARCTIC JOURNAL
