In the 1970's, a Russian biologist discovered 200 species of tiny organisms, algae and zooplankton that flourished on the ice floes, the bottoms of icebergs and in the open water of the Arctic Ocean.

These organisms are the first level of an important food chain. Their carcasses fall to the ocean bottom to nourish clams, which are eaten by walruses.

Fish live on algae scraped off the ice, and the fish are eaten by seabirds, whales, and seals. The seals are a favorite food of the polar bear - at the top of the food chain.

When the biologist visited the same area less than 20 years later, he found that most of the plankton species were gone, and the ice was nearly gone too. Creatures that lived on the plankton (fish), or depended on the ice for dens or travel (seals and bears) were gone too - forced to move farther north.

Itty-bitty organisms like plankton may seem unimportant, but when environmental changes start messing with the food chain, the damage ripples through the entire structure.