Quetin and Ross: A Long-Term Ecological Research..., Mar.Pol.Bull,1992 Palmer LTER Contribution #13 A Long-Term Ecological Research Strategy for Polar Environmental Research Langdon B. Quetin Robin M. Ross Marine Science Institute University of California Santa Barbara, California 93106 The Palmer Long-Term Ecological Research site was established in the vicinity of Palmer Station, Antarctica in 1990. It is the eighteenth and most recent addition to the LTER Network funded by the National Science Foundation of the United States. The Palmer LTER expands the geographical and habitat coverage of the LTER Network to southern polar regions and offers unique opportunities for ecological synthesis and the study of long-term ecological phenomena in the antarctic marine ecosystem. The central hypothesis of the Palmer LTER is that many significant biological processes in the antarctic marine environment are strongly affected by physical processes, particularly interannual variability in the annual extent and dynamics of pack ice and variations in ocean currents. The Palmer LTER Studies Group is multidisciplinary and seeks to understand and model interactions between key species from different trophic levels and the physical environment. It is recognized that anthropogenic impacts in Antarctica cannot be adequately evaluated without understanding the underlying natural variability in antarctic ecosystems. Text Long-term ecological patterns often elude our recognition and understanding. Magnuson et al. (1983) and Magnuson (1990) coined the term "the invisible present" to refer to the loss of information and tendency to misinterpretation when observations of the present are not placed in appropriate time and space scales. Short-term ecological phenomena that we see every day often have their origins in rare or slow processes or in events occurring on larger scales than normally studied in ecological investigations. For example, seasonal ice cover on Lake Mendota, Wisconsin, has been documented continuously since 1855. Only after many years of study could variation in ice cover be correlated with larger scale processes. Though large interannual variation in the duration of annual ice cover on the lake was frozen was seen after 10 years, only after 50 years was it apparent that years of shorter duration of ice cover and El Nino years coincided (Magnuson and Drury, 1991). Also, only after analysis of a data record longer than a century did the warming trend from the end of the "little ice age" emerge. This correlation of a cyclical seasonal process with a longer, larger scale cyclical process and a long-term trend would never have become apparent without long-term studies. To better understand larger and longer scale ecological processes, the National Science Foundation of the United States established a network for Long-Term Ecological Research (LTER) in 1981 with the founding of six research sites in the continental United States. Today the LTER Network spans 18 research sites that include a wide range of environments and diversity of research approaches (Fig. 1)--. From its inception the intent of this program was to coordinate the research at each site to enhance comparative analyses and to test theoretical constructs between sites (Franklin et al., 1990). One example of a comparative analyses is whether the pattern of primary production between sites is primarily controlled by "bottom up" variables such as light and nutrients or by a "top down" variable such as grazing? Research at each site is structured around five core areas, one of which is to evaluate the pattern and frequency of disturbance at each site (Callahan, 1984). Pollution is clearly one type of disturbance that may have effects on a site, whether it be on the scale of global warming or on the smaller scale of an oil spill. As is common to all ecosystem studies, variations in natural ecological processes need to be understood within the context of human disturbance; and possible pollution effects need to be evaluated against the pattern of natural variability in the environment, and in the plant and animal populations inhabiting the ecosystem. Polar regions are no exception. The Palmer LTER, established at Palmer Station, Antarctica in 1990, is the newest LTER site. Predictions suggest that the effects of global change (climate warming, ozone depletion, and increased human pressure on resources) will be more pronounced and thus detectable earlier in Antarctica than in mid-latitudes (Manabe and Stouffer, 1979). Our earlier detection and understanding of the cause and effect of these changes in Antarctica may serve as a model for more temperate areas. The Palmer LTER will monitor the ecological effects of changes in sea-ice extent and thickness, study the processes underlying these effects, as recommended by the International Geosphere-Biosphere Programme (IGBP)(Anon., 1989), and will build interactive models in an effort to predict the impacts of global warming and attendant changes in the annual cycle of pack ice on antarctic biota. A comprehensive strategy for any environmental research program should include long-term data bases complimented by shorter, more intensive studies of processes. For example, in the polar environment one concern is the seasonal thinning of the ozone layer over Antarctica which leads to increases in ultraviolet (UVB) radiation, and decreases total primary production (Smith et al., 1992). Complimentary research on the effects of UVB on antarctic communities, when coupled with long-term observations, will enable us to better predict future impacts. LTER Study Region The LTER study region is adjacent to and surrounds Palmer Station, located in a protected harbor on the southwest side of Anvers Island midway down the Antarctic Peninsula (64｡40'S, 64｡W) (Fig. 2). Within a 9-km radius of Palmer Station are two exposed, prominent points, and groups of islands that extend to the edge of the Bismarck Strait to the southeast. Palmer Basin, 22 km southwest of Palmer Station, is the only deep basin in the area. The maximum depth is 1280 m, and the basin is connected to the open ocean on the west side of Anvers Island, and to the southern end of the strait between Anvers Island and the Antarctic Peninsula to the northeast. ------------- The climate is typically maritime Antarctic, with snow and rain common any time of the year. The temperature at Palmer Station is relatively mild, averaging about -10｡C in July and 2｡C in January, with temperature extremes recorded at -31｡C and 9｡C. Annual rainfall averages about 10 inches and snowfall about 14 inches. Two large scale physical processes impact the Southern Ocean ecosystem: the seasonal advance and retreat of pack ice, and oceanic circulation patterns. The central hypothesis of the Palmer LTER states that many significant biological processes in the antarctic marine environment are strongly affected by physical factors, particularly the annual advance and retreat of pack ice and variations in ocean currents. In polar environments, the annual advance and retreat of the pack ice is an important physical feature covering vast areas of the marine environment (Garrison and Siniff, 1986). In the Southern Ocean this seasonal cycle of ice formation and melting affects about 50% of the open sea. The amplitude and phase of interannual variability in the regional extent of pack ice is not the same in all sectors of the Southern Ocean (Zwally et al., 1983). In the region around Palmer Station the maximum extent of pack ice varies widely, from near zero to halfway across Drake Passage (Quetin and Ross, 1991), and in recent years has been on a 6 to 8 year cycle (personal communications). The timing of the onset of ice formation also varies systematically from late May to August. Pack ice not only provides marine habitats distinct from open-water habitats, but also may be the major physical determinant of temporal/spatial changes in the structure and function of polar biota (Fraser and Ainley, 1986). Thus interannual cycles and/or trends in the annual extent of pack ice are likely to have significant effects on all levels of the food web, from total annual primary production to breeding success in seabirds. ---- Mesoscale oceanic circulation patterns are reasonably well- known (Hofmann et al., in press). A southwest setting flow (East Wind Drift, EWD), beginning around Anvers Island, feeds into a cyclonic eddy about 300 km south and seaward of the EWD. The Antarctic Circumpolar Current (ACC) flows northeast on the outside of this gyre. However, the geographic position of the ACC varies (Gordon, 1988) over many kilometers. The ACC also generates eddies that may persist for a month or so and extend tens of kilometers (Nowlin and Klinck, 1986). Changes in the timing of the seasonal change in wind direction and thus Ekman stress (Capella, 1989) may also affect the strength of the EWD. Shifts in water masses and changes in local current regimes may impact distributions and food availability to many marine communities. Palmer LTER Research Objectives The overall objectives of the Palmer LTER are: (1) to document interannual variability in the development and extent of annual pack ice in the seasonal cycle of large groups of primary producers (diatoms, prymnesiophytes) and in populations of key species from different trophic levels (Table 1); (2) to quantify the processes that underlie natural variation in these representative populations; (3) to construct models that link ecosystem processes to physical environmental variables and their natural scales, and to simulate the spatial/temporal relationships between representative populations; and (4) to employ such models to predict and validate the impacts of altered periodicities in the annual extent of pack ice on ecosystem dynamics. One of our challenges is to link the different spatial and temporal scales characteristic of the different components of the ecosystem (Table 1). The inherent interannual variability in the extent of pack ice generates natural experiments on the effects of pack ice on the various trophic levels. The results of these experiments are the parameters and processes monitored during and after seasons of different pack ice cover. ------ Research at the Palmer LTER site will focus on the pelagic marine ecosystem and the ecological processes which link the extent of annual pack ice to the biological dynamics of different trophic levels. Although the antarctic marine food web is as complex as any other marine food web, the links between primary producers, grazers and apex predators (seabirds, seals and whales) are often short and may involve fewer than three or four species (Fig. 3). Predators tend to concentrate on a core group of species, especially some extremely abundant euphausiids and fish close to the base of the food web. Our general approach capitalizes on this close coupling between trophic levels, the limited number of species involved, and the fact that the dominant predators are seabirds that nest on land and are easily accessible during the spring and summer breeding season. Thus aspects of seabird foraging and reproductive biology can be used as indices of local and short-term prey abundance and availability, i.e. within the foraging range during the breeding period. These indices can be evaluated with greater precision than can the biomass and distribution of their prey by classical oceanographic methods. However, although aspects of the biology of dominant consumers may be good indices of local prey abundance and availability, they may not be reliable indices of the regional population dynamics of the prey species. Ad四ie penguins dominate the seabird assemblage, but the islands and points of land in the area also support chinstrap penguins and south polar skuas. Ad四ies from Palmer Station are believed to winter in the pack ice of the Bellingshausen Sea near to Palmer. About 600 pairs of south polar skuas also reside on about a dozen islands in the vicinity. During the summer breeding season, these seabirds depend on resources in the adjacent deep-water foraging area: 50 km radius for the Ad四ies, 100 to 160 km for the south polar skuas. Their major prey items, antarctic krill and silverfish respectively, are found within Palmer Basin, within the EWD and on the eastern edge of the ACC. Initial studies will examine the mechanisms behind changes in prey levels within the summer foraging area - such as changes in water mass distribution, variability in reproductive and recruitment success of the prey, and changes in food availability during critical periods of the prey's life history. Extreme interannual mesoscale variation in the distribution patterns of krill, which greatly impacts the predators, is likely not due to recruitment failure (Priddle et al., 1988). Recruitment failure for one year would not change the abundance of krill enough to be detectable by current sampling regimes. Poor recruitment would need to occur over a number of seasons for decreases in krill abundance to be detectable. The model of Priddle et al. (1988) predicts that krill abundance would take three years to return to initial levels after two consecutive years of recruitment failure. However, the extreme changes in krill abundance observed in a region are often seasonal or recovery occurs in a year. This timing in the change of abundance of krill indicates that changes in current patterns and eddy distribution may influence the distribution of antarctic krill and thus the prey available to seabirds. The impact of the extent of ice on the prey and predators may be direct or mediated by the effect of ice on lower trophic levels. In the Southern Ocean, pack ice affects primary production in three communities: open water communities, ice-edge blooms, and ice algae. The stable layer created by melting pack ice and increasing incident radiation in the spring promotes ice-edge blooms that precede blooms in open water in the surrounding seas. Ice-edge blooms are a significant component of total productivity in the Southern Ocean, and variation in the timing and amount of ice-edge bloom production from variation in the extent of pack ice will affect both total primary production (Smith et al., 1988) and the timing and extent of food availability to the grazers. One of our principal objectives is to separate long-term (decadal) systematic trends from large interannual variability in populations. This ability is vital if we are to measure the effects of increased human pressure on living resources and uphold the agreement of the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR) not to fish any living resource (including krill) to such an extent that either the population itself or consumers depending on that food item were affected. With the Palmer LTER we expect to understand the processes underlying interannual variability, and thus be in a position to separate changes due to natural cycles from those due to systematic trends. Understanding natural variability within the antarctic marine environment is fundamental to our understanding of the more subtle impacts of humankind. Acknowledgements Other Palmer LTER Principal Investigators: W. Fraser, E. E. Hofmann, J. Klinck, and W. Trivelpiece from Old Dominion University; and B. Pr斯elin and R. Smith from the University of California at Santa Barbara. The Palmer LTER is funded by the Division of Polar Programs, National Science Foundation, NSF DPP 90-11927. This is Palmer LTER Publication No. 12. References Anon. (1989) The role of Antarctica in global change: Scientific priorities for the International Geosphere-Biosphere Programme (IGBP). SCAR Steering Committee for the IGBP. ICSU Press, 28 p. Callahan, J.T. (1984) Long-term ecological research. BioScience 34, 363-367. Franklin, J. F., Bledsoe, C. S. & Callahan, J. T. (1990) Contributions of the long-term ecological research program. BioScience 40, 509-523. Fraser, W. R. & D. G. Ainley. (1986) Ice edges and seabird occurrence in Antarctica. BioScience 36, 258-263. Garrison, D. L. & Siniff, D. B. An antarctic perspective. BioScience 36, 238-242. Gordon, A. L. (1988) Spatial and temporal variability within the Southern Ocean. In Antarctic Ocean and Resources Variability (D. Sahrhage, ed), pp. 41-56. Springer-Verlag, Berlin. Hofmann, E. E., Lascara, C. M., & J. M. Klinck. (1992) Palmer LTER: Upper ocean circulation in the LTER region from historical sources. Ant. J. U. S., in press. Magnuson, J. J. (1990) Long-term ecological research and the invisible present. BioScience 40, 495-501. Magnuson, J. J., Bowser, C. J. & Beckel, A. L. (1983) The invisible present: long-term ecological research on lakes. L & S Magazine , University of Wisconsin, Madison Fall 1983, 3-6. Magnuson, J. J. & J. A. Drury. (1991) Global change ecology. Natural Science April 1991: 304-311. Manabe, S. & Stouffer, R. J. (1979) A CO2-climate sensitivity study with a mathematical model of the global climate. Nature 282, 491-492. Nowlin, W. D. & Klinck, J. M. (1986) The physics of the Antarctic Circumpolar Current. Reviews of Geophysics and Space Physics , 24, 469-491. Priddle, J., Croxall, J. P., Everson, I., Heywood, R. B., Murphy, E. J., Prince, P. A. & Sear, C. B. (1988) In Antarctic Ocean and Resources Variability (D. Sahrhage, ed), pp. 169-182. Springer-Verlag, Berlin. Quetin, L. B., & Ross, R. M. (1991) Behavioral and physiological characteristics of the Antarctic krill, Euphausia superba. Amer. Zool. 31, 49-63. Smith, R., Prezelin, B. B., Baker, K. S., Bidigare, R. R., Boucher, N. P., Coley, T., Karentz, D., MacIntyre, S., Matlick, H. A., Menzies, D., Ondrusek, M., Wan, Z. & Waters, K. J. (1992) Ozone depletion: Ultraviolet radiation and phytoplankton biology in antarctic waters. Science 255, 952-959. Smith, W. O., Keene, N. K. & Comiso, J. C. (!988) Interannual variability in estimated primary productivity of the Antarctic marginal ice zone. In Antarctic Ocean and Resources Variability (D. Sahrhage, ed), pp. 131-139. Springer-Verlag, Berlin. Zwally, H. J., Parkinson, C. L., & Comiso, J. C. 1983. Variability of Antarctic sea ice and changes in carbon dioxide. Science 220, 1005-1012. FIGURES: Figure 1. Geographical distribution of the eighteen sites within the Long-Term Ecological Research (LTER) Network. The Palmer LTER is located in the region around Palmer Station on the west side of the Antarctica Peninsula, Antarctica. Figure 2. The west side of the Antarctica Peninsula. The region of interest for the Palmer LTER, is from Marguerite Bay to the northern edge of Gerlache Strait and seaward for 200 km. The foraging range of the seabirds during the reproductive season is indicated by two concentric circles at 50 and 100 km from Palmer Station (black dot). Figure 3. Conceptual diagram of the ecosystem (food web and environmental factors) investigated by the Palmer LTER. Open boxes indicate components with both processes and parameters measured. Shaded boxes indicate components with parameters only measured. Table. 1. Spatial and temporal scales of the Palmer LTER. Spatial Scale,(kilometer2) Southern Ocean ice cover,10^7 Bellingshausen/Amundsen Sea,10^6 Large gyres,10^6 Antarctic Peninsula Region,10^5 Palmer Basin (near field, 100 km by 100 km),10^4 Seabirds (Ad四ie penguins, south polar skuas) summer foraging (50 km by 50 km),10^3 winter range,10^5 Eddies 10^2 Silverfish population (Pleuragramma antarcticum), ~ 10^5 Krill (Euphausia superba) population ,10^6 aggregations,< 10^0 Temporal Scale (minutes) Climate seasonal cycle ( year), 0.5x10^5 episodic weather, (hours to days),10^1-10^4 ice movements (hours to weeks), 10^1-10^5 Optical variability (minutes to hours), 10^1 Phytoplankton diel cycles, (hours),10^1-10^3 blooms (turnover times)(days),10^4 Secondary Producers (life span) krill (5-7 years), 3x10^5 antarctic silverfish (~ 25 years), 10^6 Seabirds (life span) Ad四ie penguin (~12 years), 5x10^5 south polar skua (~40 years-70 max), 10^6