The seas around Antarctica are home to a rich and diverse group of species that have developed some unique ways of coping with the cold. Some Antarctic fish, for example, are the only vertebrates in the world that do not use red blood cells to carry oxygen around their bodies. But because they are so well adapted to the cold, some of these species may not be able to endure life in a warmer world. Two recent studies may highlight risks to cold-adapted species in polar waters. One study identified the warming risks to certain Antarctic species, while the second study identified some unexpectedly common species between Arctic and Antarctic waters. Taken together, the studies appear to have serious implications for these cold-adapted life forms. Climate change is likely to have a major impact on polar species.
Earth’s unique, forbidding ice oceans of the Arctic and Antarctic have revealed a trove of secrets to Census of Marine Life explorers, who were especially surprised to find at least 235 species live in both polar seas despite an 11,000-kilometer (6,800 miles) distance in between.
The scientists found marine life that both poles apparently share in common include marathoners such as grey whales and birds, but also worms, crustaceans, and angelic snail-like pteropods, the latter discoveries opening a host of future research questions about where they originated and how they wound up at both ends of the Earth.
The Antarctic shelf is an environment of extremes. The cold, oxygen-rich waters of it allow some arthropods, such as amphipods and spiders, to become “relative giants,” Dr. David Barnes and Prof. Lloyd Peck, biologists with the British Antarctic Survey (BAS) observe. Some sea stars and sponges may grow for 100 years or more.
These deep sea dwellers use among the lowest levels of oxygen of any invertebrate, most likely to adapt to the cold temperature as well as to the amount of food available to them. According to Barnes and Peck, “the appearance to an observer is of a very still environment with little obvious movement.” They point out that even some predatory echinoderms or mollusks have been recorded as moving as little as a meter in a week.
Scientific divers inspect rich, surface-dwelling communities living underwater near Rothera Research Station off the West Antarctic Peninsula. However, that environment is changing as a result of global warming. Increased ocean acidification will almost certainly lead to thinning of shells in mollusks. So far the cold waters of the Antarctic have proven an effective barrier against invasion by non-native species, but warming temperatures could allow for the arrival of crushing predators such as crabs, to which mollusks with thinner shells might be acutely vulnerable. “If alien species enter the region they have the capacity to drastically and irrevocably change these ecosystems.” says Barnes.
As for the direct impacts on organisms of warmer water, Barnes and Peck note, the evidence is contradictory. On the one hand, experiments have shown that a number of Antarctic shelf species react extremely negatively to even relatively small increases in temperature. For example, according to experimental studies, the brachiopod Liothyrella uva and the bivalve mollusk Limopsis marionensis can apparently only survive in water between 28 and 41 degrees Fahrenheit (-2 and +5 degrees Celsius). Furthermore, several species show a progressive decline in function before temperatures reach lethal levels. For example, the large bivalve mollusk Laternula elliptica apparently cannot survive in temperatures higher than 48 degrees Fahrenheit (9 degrees Celsius), but in water temperatures above 41 degrees Fahrenheit (5 degrees Celsius), it is unable to rebury itself in the sediment if removed. The limpet Nacella concinna similarly is killed by temperatures in excess of 49 degrees Fahrenheit (9.5 degrees Celsius), but even as low as 36 or 37 degrees Fahrenheit (2 or 3 degrees Celsius), 50 percent of those studied could no longer right themselves if turned over.
However, Barnes and Peck note that, notwithstanding these findings, many of the species studied are found in warmer regions north of the Antarctic, including the waters surrounding sub-Antarctic locales such as Prince Edward, Kerguelen and Macquarie Islands. Furthermore, there is some question as to the representative nature of the studied species and whether the research adequately considers the possibility that some species might be able to adapt by moving into deeper water.
Prof. Peck discussed the prospects for survival or extinction of Antarctic marine and lake life. If predictions from global climate models are correct the prospects for cold-blooded marine animals like giant sea spiders are bleak. But, by contrast, recent warming in some Antarctic lakes has allowed microalgae to thrive.
Even so, Barnes and Peck conclude that ascertaining the likely response of the Southern Ocean’s vast, rich and least interfered with fauna has urgency, as there are valid reasons to expect that the increase in ocean temperature will have a definite impact on the region’s biota. We need to detect and understand the changes that would take place.
Copyright © 2009 by Marine Science Today, a publication of OceanLines LLC