Biota of the Antarctic
- This page is part of the topic The Antarctic environment in the global system
In the Earth System, the poles fulfil a very special role. Their slowly changing physico-chemical features have engineered life processes so that organisms surviving the ensuing severe selection can prosper in such extreme habitats. It is unreasonable to investigate life in Earth’s extreme environments without also addressing the impacts of current climate changes on organisms whose adaptations to climatic conditions have slowly evolved over geological time to reach a required equilibrium. This equilibrium is delicate, and bound to be upset by rapid changes such as those that are occurring at the present time.
Evolution is the major unifying principle of biology, and evidence of the evolutionary process pervades all levels of biological organisation from molecules to ecosystems. Although the influence of evolution extends to the fauna and flora of the most isolated continent, Antarctica is not usually included among notable evolutionary sites such as the Galapagos, Hawaii, Australia, Madagascar, the East African Great Lakes and Lake Baikal (as discussed by Eastman, 2000). In fact, however, the evolution of the marine fish group Nototheniidae on the Antarctic continental shelves ranks equally to the species radiations at these other sites (see below). The exploration of remote habitats such as Antarctica has proved to be far more valuable than merely documenting the existence of unusual faunas and floras. Discoveries made at the Galapagos stimulated Charles Darwin to begin erecting the framework for evolutionary thought. Darwin's voyage in HMS Beagle (1831-36), and subsequent research by numerous scientists, has made the Galapagos the premier evolutionary site in the world. At about the same time (1839-43), James Clark Ross with HMS Erebus and Terror, and other explorers (Wilkes and Dumont d’Urville) explored the high latitudes of Antarctic coastal waters. During these voyages many distinctive species were discovered, including an endemic tribe of four seals, six species of penguins and about a dozen species of notothenioid fish, which more recent research has shown to be unique. A comprehensive picture of the fauna did not emerge and Antarctica remained for decades unappreciated as a continental island with an endemic marine fauna. Antarctica has now joined the Galapagos as a destination of tourist ships and fishing vessels, but unlike the Galapagos, whose unique fauna is mostly terrestrial, it still does not have the recognition it deserves as a centre of evolution.
In that context it is perhaps not surprising that the unique fish fauna of the Antarctic’s continental shelf, and especially that of the Ross Sea, the largest of Antarctica’s shelves (see Eastman, 2005, and Eastman and McCune, 2000) is somewhat under-appreciated. Like the fresh-water fishes of Lake Baikal or the birds of the Galapagos and Hawaii, most Ross Sea fishes are derived from a common ancestor, and are now recognized within a single group, the notothenioids. Unlike elsewhere in the world, the Eocene fauna of the Antarctic continental shelf, particularly the Ross Sea, has been completely replaced by a modern fauna dominated by this single group. In isolation and in the absence of competition they have come to dominate the Ross Sea’s species diversity, abundance and biomass at levels of 77%, 92% and 91%, respectively. This is unique in the marine realm. They are also one of the few examples of a marine “species flock”. Some of the most recent molecular phylogenies suggest that the neutrally buoyant water column group, including toothfish (Dissostichus mawsoni) and silverfish (Pleuragramma antarcticum), was the first clade (group) to diversify into this habitat about 15-20 million years ago.
The Antarctic and its biota command increasing attention in a world attuned to changes in global climate, loss of biological diversity and depletion of marine fisheries. The links between long and short-term global climate change and evolution are among the least understood natural events in the history of the Earth. Excellent examples are available for study in the Antarctic, but will be lost if areas of the Southern Ocean are not protected in the same way that terrestrial systems have been protected in a network of Specially Protected Areas. For instance, the nototheniid fauna of the northern insular shelves, e.g. Scotia and Kerguelen, has been devastated by industrial fishing (Kock, 1992, 2007). Understanding the impact of past, current and predicted environmental change on biodiversity and the consequences for Antarctic-ecosystem adaptation and function is a primary goal. The critical examination of Antarctic ecosystems undergoing change provides a major contribution to the understanding of evolutionary processes of relevance to life on Earth. How well are Antarctic organisms able to cope with daily, seasonal and longer-term environmental changes? Will climate change result in relaxation of selection pressure on genomes, or tighter constraints and ultimately extinction of species and populations? The Antarctic holds great potential for evolutionary studies, through which evolutionary biology can play an important role in understanding the biological response to climate change within the whole Earth system.
There is evidence that climate change and modifications of the Earth system occur at faster rates than elsewhere in the polar regions. The uniquely adapted fauna of these regions is vulnerable to shifts in climate. Therefore, it is urgent to establish the state of these communities, and in particular their diversity, as well as to protect them from direct human impacts (e.g. fishing), if we are to understand the impacts of climate change. These impacts will have many types of consequences, among which the loss of biodiversity is of highest concern. To reliably assess the extent of future changes in polar ecosystems, a mass of data should be aggregated to identify undisputable evidence of change in ecosystem structure/functioning/services. Sound science plans, efficient data management and an unprecedented collaborative research effort in the International Polar Year framework and beyond will provide scientists, environmental managers and decision-makers with a solid benchmark against which future changes can reliably be assessed. Studies of the biodiversity of polar marine organisms, coupled to sound data handling and dissemination, within a network of protected areas, will bring a better understanding of how life has evolved in the marine environment of the poles, and to what extent it may potentially respond to change. Bridges between different research disciplines and international programmes will not only bring a crucial support to polar science, but will provide a legacy of knowledge for future generations in the form of a sustainable information system.
All organisms and the communities to which they belong are shaped by both ecological and evolutionary factors. On longer time scales, marine, lake, and terrestrial assemblages reflect the influence of evolutionary events, invasions, extinctions, tectonics and climatic change. Evolutionary processes in the biosphere have developed efficiently under specific Antarctic conditions for the past 30 million years, and it is these processes that are most closely linked to future developments, since it is adaptation that governs the survival or extinction of species and communities. On shorter time scales organisms and communities are shaped by ecological factors such as dispersal, predation, competition, habitat, disturbance, food supply, and pure chance.
Pages in this topic
- Eastman, J.T. 2000. Antarctic notothenioid fishes as subjects for research in evolutionary biology, Antarctic Sci., 12, 276-287.
- Eastman, J.T. 2005. The nature of the diversity of Antarctic fishes, Polar Biology, 28, 1432-2056.
- Eastman, J.T. and McCune, A.R. 2000. Fishes on the Antarctic continental shelf: evolution of a marine species flock? Journal of Fish Biology, 57, 84-102.
- Kock, K.-H. 1992. Antarctic Fish and Fisheries. Cambridge University Press, Cambridge and New York, 359 pp.
- Kock, K.-H. 2007. Antarctic Marine Living Resources – exploitation and its management in the Southern Ocean, Antarctic Science, 19, 231-238.