By Carla Sabotta, Olympia, Washington.

From jellyfish to harbor seals, a variety of animals thrive in and around icebergs. The animals find food and shelter, and some of them nest, on these floating chunks of ice.

Icebergs break off from glaciers and ice shelves and bob in the sea. An ice shelf appears where a glacier flows down to a coastline. Icebergs stay afloat even though they weigh many hundreds of thousands of tons. They float for the same reason ice cubes do in a glass of water—ice is lighter than water.

Icebergs the size of houses and large buildings form each year in the Arctic at the North Pole and in Antarctica at the South Pole. Table-shaped icebergs have steep sides and flat tops. Other shapes of icebergs have domes and spires.

Algae and phytoplankton grow on and around all shapes and sizes of icebergs. Algae are like plants and make food from sunlight. Phytoplankton are tiny living things and include plants and animals. Inch-long, shrimp-like creatures called krill eat the algae and phytoplankton. Thousands of krill mill about together and make up the largest part of the diet of many animals.

Invertebrates such as jellyfish come to the icebergs to feed on krill. Invertebrates lack backbones. Larger animals such as fish, squid and penguins also like krill. Penguins catch the slippery creatures with their spiny tongues and powerful jaws, while keeping a look out for seals and whales.

Leopard seals and killer whales seek out icebergs to hunt the penguins. Squawking flocks of petrels and other flying seabirds circle overhead looking for food. The seals also like to sleep on pieces of sea ice floating in the shadows of the icebergs, to get protection from high winds.

In addition to supplying food, icebergs also give protection and a place to raise pups. Young icefish dart into small holes to hide from animals hunting them. These pale-looking fish have clear blood because they lack red blood cells and hemoglobin. Groups of harbor seals haul out onto icebergs to escape killer whales, sharks and polar bears. They rest on the ice with their heads and rear flippers lifted up in a banana-like pose.

During the spring, female harbor seals give birth to pups on icebergs. Groups of mother seals raise their pups on the ice to protect themselves from predators. When they’re not swimming and diving, the seal pups rest on the ice. Out of the water the pups use little energy to stay warm. They can instead use the energy from their mother’s milk to grow and put on the blubber they will need to survive the winter.

Are icebergs becoming home to new animals? Possibly. Scientists recently reported for the first time seeing a colony of ivory gulls and chicks nesting on a rock-covered iceberg. The iceberg drifted in open water near Northeast Greenland. These gleaming white gulls usually build their nests on cliff ledges or distant islands near coasts. Scientists think the gulls may have chosen an iceberg to avoid Arctic foxes and polar bears, and to stay close to their favorite food—small fish and krill.

Carla adds, “I was inspired to write this article after learning about icebergs on a trip to Antarctica.”