Catching Energy Each diatom floating near the iceberg is small but mighty. In fact, without them, this food web couldn’t exist. T ey form its foundation. T ese tiny plants capture energy from
the sun. T en, through photosynthesis, they make their own food. T at makes them the producers in this food web. In most ecosystems, the producers attract a
hungry crowd. It’s no diff erent here. I soon see a swarm of krill swimming my way. As many as 10,000 of these tiny shrimp-like creatures surround me. T e krill move through the green water
gobbling up diatoms as they go. T e plants’ energy passes into the krill. It’s easy for me to figure out which ones have eaten a good meal. T rough their clear exoskeletons, I can see a green dot inside their digestive systems.
Passing Energy T e krill are just the first of many consumers in this food web. Lots of other animals, or secondary consumers, eat the krill. Comb jellies float by, pushing water and
krill toward their mouths. I see a krill trapped inside one! Other jelly-like creatures driſt by with krill tangled in their stinging tentacles. T ese krill quickly become a meal, too. A baby icefish darts out of a hole in the
iceberg, grabs a krill, and then retreats. I don’t know if the holes occur naturally, or if the fish make them. Either way, the holes keep the fish from turning from consumer into consumed—at least for now. As I pop my head out of the water, I see a
crabeater seal sunning itself on the ice. In spite of its name, this seal mostly eats krill, too. So do the Adélie penguins swimming around the iceberg. Energy that started with the sun now is spreading from consumer to consumer.
6 NATIONAL GEOGRAPHIC EXTREME EXPLORER
Up the Food Web Krill aren’t the only animals on the menu. On one dive, I swim through a patch of jelly-like creatures. Suddenly, I see splashes all around me. Birds are diving into the sea above my head and snatching the jellies in their bills. I’ve also seen bigger comb jellies gobble
up smaller ones. T en there’s the time I saw a leopard seal chase a penguin around an iceberg. Its jaws snapped every time it got close to the bird. Finally, it grabbed the penguin, shook it hard, and swallowed it. It’s not a pretty sight, but I know it’s how
energy moves from organism to organism here. With each meal, the web widens. Even the leopard seal isn’t safe from becoming a meal. It needs to watch out for an even bigger consumer—an orca.
Islands of Life As I head back to Braveheart, I think about what I’ve learned. Icebergs are islands of life. T ey release nutrients as they melt. T ese nutrients fertilize the base of this ocean food web so tiny plants can grow. As energy from the sun passes from organism to organism, a circle of life forms around each iceberg. We pass dozens more icebergs on the way
home. Each one supports its own food web. I’ll never look at icebergs the same way again.
Wordwise
consumer: an organism that gets its energy by eating other living things
ecology: the relationship between groups of living things and their environment
food web: the transfer of energy in overlapping food chains within an ecosystem
producer: an organism that makes its own food from light energy
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