Seaweed

Seaweed, or macroalgae, includes thousands of species of large, plant-like algae found in the ocean. These species belong to groups such as red Rhodophyta, brown Phaeophyta, and green Chlorophyta. Some types of seaweed, like kelps, are very important because they give young fish and other sea creatures a safe place to grow. They help keep our food sources safe. Other types of seaweed, such as tiny floating algae, play a big role in catching carbon from the air and making at least half of the oxygen we breathe on Earth.

Sadly, natural seaweed areas sometimes get damaged by things people do. For example, using machines to pull up kelp from the sea floor destroys these important plants and the animals that depend on them. Other problems, like a sickness that affects animals which normally keep certain sea creatures in check, can also hurt seaweed areas. One such problem has caused many purple urchins to grow out of control, destroying big kelp forests off the coast of California.

People have been using seaweed for a very long time. Today, growing seaweed has become an important farming activity all over the world. Seaweed is used for food, to make useful chemicals like carrageenan, and even as food for animals or to help plants grow. Because seaweed is so important for sea life and for taking in carbon dioxide, scientists are looking at ways to grow more seaweed. This could help fight climate change by taking carbon out of the air, cleaning up extra nutrients in the water, giving more homes to sea animals, and helping to balance the chemistry of the ocean. The special report from the IPCC suggests that more study is needed to make this a useful way to protect our planet.

Taxonomy

"Seaweed" is a word we use for plants and algae that live in the ocean and can be seen without a microscope. It includes flowering plants like eelgrass and larger marine algae. Seaweed mainly belongs to three groups: red, green, and brown algae. Even though these groups look similar, they do not share one common ancestor that had many cells, so they are called a polyphyletic group. Sometimes, blue-green algae called Cyanobacteria are also talked about when people write about seaweed.

Scientists are still figuring out exactly how many kinds of seaweed exist, but there are probably thousands of different species.

Genera

The following table lists a very few example genera of seaweed.

Anatomy

Seaweed looks a bit like plants on land, but it is not a plant. It has different parts, such as a body called a thallus. The thallus includes a flat, leaf-like part called a lamina, which may have clusters of spores and special air pockets that help it float. Some seaweed even has a stem-like part called a stipe and a root-like part called a holdfast that keeps it stuck to the ocean floor. Together, the stipe and blade are known as the frond.

Ecology

Seaweed needs seawater or brackish water and enough light to make food through photosynthesis. They usually grow in the littoral zone, which is near the shore, especially on rocky areas rather than sandy ones. Some seaweed, like Sargassum and Gracilaria, float freely instead of being attached to the sea floor.

Seaweed can live in many different places. Some grow at the water’s surface, while others attach to the bottom several meters deep. In some places, seaweed can stretch for miles out to sea. The deepest seaweed are red algae, and some types live in tidal rock pools where they must handle quick changes in temperature, salt levels, and even drying out.

Seaweed plays an important role in the ocean. When seaweed shed old parts, these become food for animals living near the shore. Some parts of seaweed can float away and travel far out into the deep ocean, where they also provide food for deep-sea creatures. Through photosynthesis, seaweed take in carbon dioxide and release oxygen, helping to store carbon in the ocean when their parts sink to the deep sea floor.

Production

As of 2019, about 35.8 million tonnes of seaweed were produced. Most of it, around 97%, came from countries in Asia.

Farming

Uses

Seaweed has many uses. People grow or collect it for different purposes.

Food

Main article: Edible seaweed

Seaweed is eaten in many parts of the world, especially in places like Japan, China, Korea, and Taiwan. It is also eaten in Southeast Asia, such as Brunei, Singapore, Thailand, Burma, Cambodia, Vietnam, Indonesia, the Philippines, and Malaysia. Other places where seaweed is eaten include South Africa, Belize, Peru, Chile, the Canadian Maritimes, Scandinavia, South West England, Ireland, Wales, Hawaii, California, and Scotland.

Some types of seaweed, like Gim from Korea, nori from Japan, and zicai from China, are dried and used in soups, sushi, or rice balls called onigiri. In the Philippines, dried seaweed called Gamet is used to add flavor to soups, salads, and omelettes. Other seaweed is used to make food additives.

Seaweed can also be used as food for animals. It has been eaten by sheep, horses, and cattle in Northern Europe. It can help reduce certain gases from cows when added to their food.

Medicine and herbs

See also: Fucoidan

Some parts of seaweed are used in medicine. For example, certain seaweed materials are used in wound dressings and in dental molds. Seaweed extracts are also used in some diet pills to help people feel full.

Paper and packaging

Seaweed can be turned into a material for packaging or made into paper.

Climate change mitigation

Further information: Carbon sequestration and blue carbon

Seaweed is a resource that can be used again and again.

Other uses

See also: Seaweed fertilizer and Seaweed fuel

Seaweed can also be used as fertilizer for plants, to help hold down sand on beaches, or even as a possible source of fuel. It is used to make things like toothpaste, cosmetics, and paints. People sometimes collect and press seaweed as a hobby.

_Onigiri__ and _wakame__ _miso soup__, Japan

[Laverbread](/wiki/Laverbread) and toast

Small plots being used to farm seaweed in [Indonesia](/wiki/Indonesia), with each rectangle belonging to a different family

Health risks

Rotting seaweed can produce a harmful gas that may make people very sick. This gas can cause people to feel very unwell, with symptoms like throwing up and having stomach trouble.

Some types of seaweed, called "stinging seaweed," can hurt the skin if touched. When this seaweed touches the skin, it can cause a painful rash that lasts for several days.

Threats

Some seaweeds can get sick from bacteria. For example, a disease called ice-ice makes red seaweed turn white and has caused big losses in places like the Philippines, Tanzania, and Mozambique.

In some areas, sea urchins have taken over spots where kelp forests used to grow. These urchins can live for more than 50 years and sometimes work together to find food when they are hungry.