Plankton range in size from crustaceans such as krill, that are almost the length of your hand, to some that are so small they can only be seen with a microscope. The smallest (called phytoplankton) are essential for the health of our planet as they release oxygen and absorb carbon dioxide (the main greenhouse gas) from the atmosphere, which they recycle as carbon into the seabed. We humans depend on plankton more than we realize, and if we harm the oceans - as we are currently doing – we are really harming ourselves.
Some of the very tiniest of the plankton actually live within the ice on the bottom of the floes. When our ship is smashing its way through the pack ice, the broken pieces often flip over and we find that their undersides are coffee-colored. This is the phytoplankton. Life within the ice.
Of the larger plankton, the best known are the krill. It can be argued that krill are the most important animals in the Antarctic because of the vital role they play in the food chains. Krill eat a wide variety of tiny plankton, but then everything that is bigger (birds, penguins, fish, seals and whales) eats krill. That is why scientists talk of the food chains in Antarctica being wasp-waisted (or hourglass shaped), with krill as the so-called lynchpin species in the middle.
Climate change, pollution, ocean warming, acidification and over-fishing are causing the krill population to shrink. You can see why this is worrying, because if it continues and the krill disappear, most of the animals above them in the food chain will suffer. Consider, for example, the blue whale. It is an exclusive krill eater, taking in almost a hundred pounds at a gulp.
