Giant kelp forest © Colla - V & W/Bruce Coleman, Inc.

The primary food for ocean animals is algae. Most ocean algae consists of tiny, floating single-celled planktonic forms. But some types grow much larger, creating immense forests. The largest algae, giant kelp, grow as tall as trees. In their shadow live other algal species that play roles similar to grass and shrubs, creating a lush, layered forest.

How can entire forests grow from nothing but algae?

Plant Parallels
Though very different biologically from land plants, kelps have evolved specialized parts that look and function like leaves, stems, and roots.

Blades are flat like leaves to collect as much sunlight as possible for photosynthesis.

Stipes carry nutrients from the upper blades to deeper parts of the kelp. Long stipes also let kelp anchored in deep water send blades upward to collect light, like stems or tree trunks.

Air-filled floats hold the kelp up because giant kelp stipes cannot stand up on their own. Unlike tree trunks, kelp stipes are flexible and sway with the waves - otherwise they would snap off in a storm.

The holdfast grips the bottom so the kelp is not swept away. Giant kelp holdfasts look like roots, but smaller species use a simple suction cup.

A World of Kelp
Though giant kelp is the tallest, most dominant species, other algae of all shapes and sizes fill out the kelp forest, creating a lush, layered habitat. Many kelp forests actually contain no giant kelp at all.

Giant kelp can reach the sunlit surface from depths of about 3 to 30 meters (10 to 100 feet). Many smaller species live in the giant kelp's shadow, like bushes beneath tall trees. Others specialize in shallow water closer to shore or grow in water too rough for giant kelp.

Some red algae live at depths greater than giant kelp. Instead of growing upward, they specialize in absorbing wavelengths of light that penetrate into deep water.

Other algal species encrust rocks in the intertidal zone, which are exposed to the air when the tides recede. Some species blanket the rocks like shaggy moss; others stand erect like stubby shrubs, or stream out like ribbons.

The Kelp Community
Kelp forests provide food and shelter for many animal species. From snails to seals, urchins to otters and birds to baby fish, countless coastal creatures are all helped by kelp.

Kelp provides the primary nutrients for a broad community of animals. Herbivores such as snails and urchins graze on the kelp directly. Fish feast on snails, isopods, crabs and other invertebrates, as well as other fish. Seabirds and marine mammals, including seals and whales, come to eat them all.

Kelp forests also provide nurseries for young fish that seek shelter in the canopy. Kelp slows the rushing water, causing small, floating plankton - including nutritious eggs and larvae - to collect among the fronds. Many animals congregate in the kelp to gobble these floating feasts.