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Updated 12 October, 2003
Antarctic Update: An Ecosystem Perspective on UV Radiation and Climate Change Impacts
USGCRP Seminar, 2 June 1997
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What are the effects of recent climate changes on Antarctic ecosystems and what are the implications for the future? Is there a relationship between ozone depletion and higher levels of ultraviolet (UV) radiation reaching the surface in the Antarctic region? What effects have seasonally increased levels of UV-B radiation had on Antarctic ecosystems? How will these changes affect other ecosystems and food webs?

INTRODUCTION:

Dr. Cornelius W. Sullivan
Director, Office of Polar Programs, National Science Foundation, Arlington, VA

SPEAKERS:

Dr. William R. Fraser
Biology Department, Montana State University, Bozeman, MT

Dr. Deneb Karentz
Departments of Biology and Environmental Science, University of San Francisco, San Francisco, CA

Overview

Dr. Fraser and Dr. Karentz have concluded the following regarding the impacts of ozone depletion and climate change in the Antarctic: 1) Changing patterns of snow deposition and melt are affecting summer nesting habitats of penguins in the West Antarctic peninsula by producing a mismatch between the availability of breeding habitat and the requirements of penguins at various stages in their breeding cycle; 2) these changes are consistent with there having been warming in certain regions of the West Antarctic on the order of 4-5°C, which are values generally consistent with observations and model predictions; 3) those Antarctic species found at the periphery of their breeding ranges are most likely to undergo pronounced changes due to climate change; 4) Antarctic marine organisms have different sensitivities to UV exposure; 5) the amount of biological damage to Antarctic marine organisms due to UV-B radiation is directly correlated to the level of ozone depletion; 6) increased levels of UV-B radiation in the Antarctic can, and do, result in impairment of metabolic processes, decreases in growth, reduction in reproductive potential, morphological abnormalities, genetic damage, and death; and 7) UV-induced damage to marine organisms can further lead to the disruption of entire ecosystems and food webs—therefore, the availability of food resources for humans and other ecosystems.

Long-Term Changes in Certain Antarctic Predator Populations: Evidence of Climate Warming in the Western Antarctic Peninsula

It is estimated that a century ago the number of baleen whales feeding in the Antarctic during summer totaled about one million, with a biomass of 43 million tons. These whales fed primarily on a small crustacean, the Antarctic krill, taking an estimated 190 million tons annually. By the 1930s, commercial whaling had reduced the whale population to about 340,000 individuals, and today the current biomass probably does not exceed 7 million tons, or about one-sixth of the initial stock.

A central tenet of Antarctic ecology holds that the depletion of baleen whale stocks resulted in a "krill surplus." Documented increases in the abundance of krill-dependent predators such as seals and penguins following the collapse of whale stocks have thus been attributed to the effects of competitive release, or the idea that, without whales, other predators benefited from the increased availability of krill. Although this hypothesis has been one of the dominant elements guiding the interpretation of data related to Southern Ocean food web dynamics, close inspection of the long-term population trends of some of these predators has revealed patterns that are inconsistent with this model.

These trends, based on two ecologically similar penguins (Chinstrap and Adelie) found on the Antarctic Peninsula, suggest these species are tracking the effects of a warming trend that is affecting the availability of critical winter and summer habitats. The suspected mechanism appears to involve a decrease in the frequency of cold years with heavy sea ice, which represents critical winter habitat. Changing patterns of snow deposition and melt, perhaps related to the absence of winter sea ice as well, are also affecting summer nesting habitat, producing a temporal mismatch between the availability of breeding habitat and the requirements of penguins, for example, at various stages in their breeding cycles. These observations support the predictions of a number of climate model studies with respect to where pronounced climatological—hence ecological changes—are likely to occur (polar environments), what species will be affected (those found at the periphery of their breeding range), and what biophysical processes may be involved (the disruption of evolved natural history patterns by changing the timing of physical events). These observed physical changes, as well as changes in patterns of behavior, are consistent with expectations of the consequences of the observed regional increase in mid-winter temperatures of 4-5°C over the past half century.

Ecological Considerations of Antarctic Ozone Depletion

Global-scale ozone depletion attributed to anthropogenic pollution of the atmosphere was predicted by scientists more the 20 years ago. Ozone is a natural component of the Earth's atmosphere, and ozone specifically absorbs in the UV portion of the solar spectrum. Even under a "normal" ozone column, harmful UV-B radiation passes through to the Earth's surface. Ozone depletion results in an increase in the amount of biologically harmful UV-B radiation that reaches the Earth's surface and that penetrates into the surface waters of the oceans.

UV-B is biologically harmful, primarily because UV-B is absorbed by key biological molecules such as nucleic acids (DNA) and proteins. Absorption of UV causes structural damage to these molecules, changing their physical shape and interfering with the specific functions they provide for life. Dr. Karentz and her colleagues have observed and documented, for example, that increased levels of UV-B radiation in the Antarctic provoke a range of changes in marine organisms, such as impairment of metabolic processes, decreases in growth, reduction in reproductive potential, morphological abnormalities, genetic damage, and death. Thus, the evidence suggests that UV-induced damage to specific organisms can initiate various degrees of disruption in marine ecosystems, upsetting the balance between organisms and their environment.

Research conducted in the Antarctic indicates that the amount of biological damage to marine organisms is directly correlated to the level of ozone depletion. It has also been observed that Antarctic organisms have differential sensitivities to UV exposure such that a dose of UV that is lethal to one species may only cause impairment in another. The degree of tolerance is dependent on 1) the effectiveness of protective strategies that serve to minimize damage by reducing exposure to UV-B, and 2) repair mechanisms that can correct UV-B induced damage. The combination of protection and repair capabilities varies among species and will influence survival, growth, and reproductive success under UV-B stress. Because each species responds differently, shifts in species composition (biodiversity) are expected under an increased UV-B regime. Even subtle alterations in the quantity or quality of food sources (phytoplankton and krill) can ultimately affect the larger Antarctic consumers such as penguins, seals, and whales. Because the Antarctic marine ecosystem is directly linked to the rest of the world's oceans, changes in the Antarctic region can initiate changes in the rest of the biosphere. We need, therefore, to understand better what these changes might be and what impacts they could have on humans and other ecosystems.

Biography of Dr. William R. Fraser

Dr. William R. Fraser is currently an Assistant Professor in the Polar Oceans Research Group of the Biology Department at Montana State University in Bozeman, Montana. His research interests focus on understanding the physical and biological interactions that control the distribution and demography of seabirds. His present research on the Antarctic Peninsula began in 1974, while he was at the University of Minnesota, and has continued to the present, evolving into a program that employs basic and applied approaches to investigating issues involving the effects of climate change, fisheries, and tourism on Antarctic ecosystems, especially seabird communities. Dr. Fraser's work has emphasized long-term research, the rationale being that the scale of the effort needs to match the scale of the processes under investigation, and ecological time scales involve decades to centuries. It was this focus that in 1992, nearly 2 decades after his research began, led him to propose that changes in sea ice conditions due to climate warming were having a significant impact on the Antarctic ecosystem. Although other researchers had suggested a possible climate effect, none had identified a mechanism by which changes in the physical environment might lead to ecosystem-level responses. This work became one of the founding hypotheses supporting long-term research in Antarctica as part of the National Science Foundation's prestigious Long-Term Ecological Research Program. Dr. Fraser is currently a U.S. representative to the Scientific Committee on Antarctic Research, Bird Biology Subcommittee, and annually contributes data and advises national and international programs concerned with management of Antarctic marine living resources. He received his B.S. degree in Wildlife Management from Utah State University in 1973, and his Ph.D. degree in Wildlife Ecology from the University of Minnesota in 1989.

Biography of Dr. Deneb Karentz

Dr. Deneb Karentz is a Professor in the Departments of Biology and Environmental Science at the University of San Francisco. She has studied the UV-photobiology of Antarctic organisms since 1987, and was one of the first scientists to document the biological effects of Antarctic ozone depletion. Dr. Karentz's research has underscored the importance of understanding species-specific responses to UV exposure as a vital component in evaluating the ecological consequences of ozone depletion. Her current research program focuses on characterizing tolerance (protection and repair) mechanisms that determine the UV sensitivity of organisms. Dr. Karentz has participated in a number of workshops and symposia relating to the biological effects of UV exposure and the potential impacts of ozone depletion on ecosystem change. These include meetings sponsored by the Scientific Committee on Problems of the Environment (SCOPE), the NATO Advanced Science Institute Series on Global Environmental Change, the International Congress of Scientific Unions (ICSU), Woods Hole Oceanographic Institution and the American Association for the Advancement of Science (AAAS). She has received the Luigi Provasoli Award in Recognition of an Outstanding Paper published in the Journal of Phycology and the Arthur Furst Award for Outstanding Research from the University of San Francisco. Dr. Karentz's academic background is in marine biology. She has an M.S. degree from Oregon State University (1976) and a Ph.D. from the University of Rhode Island (1982). Dr. Karentz was a National Research Service Award Post-Doctoral Fellow at the University of California Medical Center in San Francisco (1983-1986), and is an instructor in the National Science Foundation Antarctic Biology Course held at McMurdo Station, Antarctica (1994, 1995, 1996).


 

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