Forests beneath the waves

Imagine walking into a forest where the trees sway instead of creak, where light arrives in shifting beams and where the canopy floats. That is a kelp forest, and it is one of the most lively places in the sea.

Not trees, not even plants

Kelp looks like vegetation, but it is something else. NOAA describes kelp as large brown algae. They live in cool, relatively shallow water close to the shore and grow in dense groups — so dense that, like trees on land, they form a forest.

Those groups need light to photosynthesise. That is why kelp forests stay in shallow, open water and are rarely found deeper than about 15 to 40 metres.

Astonishing growth

In ideal conditions, kelp can grow up to about 45 centimetres in a single day, according to NOAA’s National Ocean Service. Giant kelp canopies tower above the ocean floor — a striking contrast with colourful, slow-growing corals.

Fast growth matters, because these forests also take damage. Storms and large weather events such as El Niño can tear and dislodge kelp, leaving a tattered winter forest that begins to regrow each spring. Like a forest on land, a kelp forest changes with the seasons.

A crowded neighbourhood

Kelp forests support a greater variety of plants and animals than almost any other ocean community. Thousands of species of fish, invertebrates and marine mammals find food or shelter there. Many use the thick blades as a nursery, a safe place for young animals to hide from predators or rough weather.

The visitor list is long. NOAA names seals, sea lions, whales and sea otters among the mammals, and gulls, terns, snowy egrets, great blue herons and cormorants among the birds that use kelp forests for protection or feeding.

The urchin problem

A forest this productive also attracts grazers. Sea urchins feed on kelp, and when their numbers are not kept in check they can damage a forest badly. Sea otters eat urchins, and conservation group Oregon Wild notes that otters have been shown to help maintain and even help recover kelp forests for exactly that reason.

It is a vivid example of how a single animal can shape a whole landscape — even one underwater.

Watching for change

Because kelp forests change naturally, telling a normal season from a lasting problem takes patience. NOAA scientists monitor kelp forests by returning to the same locations again and again, recording which organisms are present and in what numbers. Over time, that record shows whether a forest is changing and helps reveal whether the cause is natural or human.

Why it matters

Kelp forests turn sunlight into shelter and food for thousands of species. Protecting the water they grow in — and the animals that keep them in balance — keeps one of the ocean’s great forests standing.