Friday, December 28, 2007

Rich life emerges from nature's freezer

Objects of attention; juvenile polychaete worms in the lab The Arctic ice supports, literally, the polar bear, a half-tonne behemoth of creamy-white fur and muscle and claws you would not argue with। It is highly visible and hugely iconic. But just as the tiger and the rhinoceros depend on creatures you cannot see without a microscope and would not willingly give house room to if you could, so does the polar bear stand, literally, on a patchwork lattice of invisible, miniscule life. Life-forms such as polychaetes (or bristleworms), copepods and amphipods that live just under the ice, around its edge, or even inside the floes themselves. "There are polychaetes, for example, which have juveniles or larvae that instead of living in the water column as they usually do, they go into the ice," Bodil Bluhm relates. "And the sea ice consists of crystals, of course; and between the crystals, there's a liquid network of brine channels, and this network houses algae, and the ice algae are abundant at a time when the water column has very little food." The channels are a good place for the larvae to find food, and also to hide from anything that might want a polychaete infant for dinner. Eventually you would run into a mismatch, where the ice melts before they're ready to have their larvae Bodil Bluhm The significance for things that you might care more about? In a nutshell, the vast and complex food web that spans the Arctic; from the centre to the continental shores, the floating ice down to the vast seafloor canyons, the insignificant algae to the majestic top carnivores. Temperatures are rising faster in the Arctic than just about anywhere else on Earth. If you want to understand how that will affect life we can see, you have to know what it means for organisms like the polychaete larvae. Tiny creatures When I meet Bodil Bluhm and her husband and research partner Rolf Gradinger, the sun is hot over the University of Alaska campus in Fairbanks, and the harsh realities of Arctic ice seem a world away. The family team has recently been completed by young Tuuli, who objects loudly to my worst questions and babbles sweet nonsense the rest of the time. She already has an ice-borne species named after her, and you suspect her life will not lack for scientific stimulation or opportunities to travel. Field tripIn the lab around the corner from Professor Bluhm's office where we chat are trays filled with larvae brought back from the ice offshore at Barrow on the northern Alaskan coast. "In the sea ice they are probably at the top of the food chain, these juveniles," says Professor Gradinger. "They are living on algae, and you find bigger algae in the ice channels, bigger by a factor of 10, than you will find in the water column. "So we keep them in the fridge and we give them different amounts of food to see how they will grow. We give them different fractions of algae of different sizes, to see what is the size range of algae they would go for. And we see how tolerant they are of salinity, because it is much saltier in the ice than in the water column." I peer down a microscope at a couple of samples of Scolelepis squamata. One juvenile, small and ill-fed, languishes lethargically in its dish; a second, bursting with algae-derived vigour, wriggles across its liquid home like a disfigured but enthusiastic sperm. It is clear which is having the better diet and the better time. Polar mismatch The rich supply of algae inside the Arctic ice probably allows animals like polychaetes to reproduce early in the year, when food is too scarce for larvae to grow in the water. Even the basic question of how much productivity occurs in the ice and how much in the water is not resolved Rolf Gradinger By going into the ice they secure a super-rich food source. Early reproduction means the adult worms can reach their homes on the seafloor before some competitors. If Arctic temperatures continue rising, if the ice melts earlier and freezes later each year, conditions will change for the polychaetes. "Eventually you would run into a mismatch, where the ice melts before they're ready to have their larvae," comments Professor Bluhm. Even the most cataclysmic forecasts of climate change do not envisage the Arctic becoming ice-free in the near future. Summers may be devoid of floating ice within half a century; but a pack will still form every autumn and last through to the following spring. The worms wriggle for Bodil Bluhm under the microscope The polychaetes of the Barrow coast will probably find a way to survive. But a shorter ice season may bring serious impacts for other microscopic Arctic creatures and the food chains they support. In the central reaches of the Arctic, varieties of amphipods, tiny crustaceans, pick algae from the bottom of the ice. They are eaten in turn by Arctic cod, from whence the food chain leads to birds, seals, and polar bears. And the amphipods, Rolf Gradinger believes, may be more sensitive to ice-free summers than the offshore polychaetes, with potential implications for everything that lives on them. Model future In principle, the data that Professors Bluhm and Gradinger acquire could be combined with computer models of climate to paint future pictures of the Arctic ecosystem. You could map how the anticipated changes to ice formation and stability would alter light penetration, salinity, and conditions for polychaetes and other microscopic denizens. You could begin to predict a biological Arctic future as well as a climatological one. But much more data is needed before that idea can become meaningful reality; data on individual species and how they interact, data on those whose lives (like the polychaetes) span the ocean from top to bottom, data on how organisms and systems are varying over time. There is a need for core information from all over the Arctic That is why this Fairbanks team has been such a prominent force in the Census of Marine Life (CoML), a 10-year international project gathering badly-needed baseline data across the world's oceans. That is why they have taken leadership of the Arctic Ocean Diversity project under the aegis of International Polar Year (IPY), a project aiming to fill gaps in the existing knowledge of Arctic marine life, and to integrate what we do know. As Professor Gradinger says, some basic questions remain to be answered about how the different parts of this world fit together. "An amazing, fascinating part about the Arctic is this strong connectivity between different habitats - the ice, the water column and the sea floor," he says. "And even the basic question of how much productivity occurs in the ice and how much in the water is not resolved." Understand the web of life better, and a picture of how it may change in a warmer world should become clearer. For Rolf Gradinger and Bodil Bluhm, concerned parents as well as concerned scientists, it is a priority that makes perfect sense.
By Richard Black Environment correspondent, BBC News website

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