Algaculture is a type of aquaculture that involves growing different kinds of algae. Most algae that are farmed are microalgae, which are also called phytoplankton, microphytes, or planktonic algae. Macroalgae, which are commonly known as seaweed, are also used in many commercial and industrial ways. However, because of their size and the specific conditions they need to grow, they are harder to farm. Newer seaweed farming methods, such as algae scrubbers that use air bubbles in small containers called tumble culture, may make this easier in the future.

Algae farming has many uses, including making nutraceuticals like omega-3 fatty acids (as algal oil), natural food colorants and dyes, food products, fertilizers, bioplastics, chemical raw materials, protein-rich feed for animals and aquaculture, medicines, and algal fuel. It can also help control pollution and capture carbon from the air.

The global production of farmed aquatic plants, mostly seaweed, increased from 13.5 million tonnes in 1995 to over 30 million tonnes in 2016 and 37.8 million tonnes in 2022. This growth was mainly driven by production increases in China, followed by Malaysia, the Philippines, Tanzania, and the Russian Federation.

Cultivated microalgae are already used in many areas of the growing bioeconomy. Research shows that algaculture has the potential to support the development of a healthy and sustainable food system in the future.

Uses of algae

Several types of algae are grown for food. Algae are a good source of food because they can produce proteins, fats, and carbohydrates that are easy to digest. They also contain important fatty acids, vitamins, and minerals. Algae can grow a lot of protein in a small area. However, there are challenges in moving from small-scale algae farming to large-scale production for food markets.

• Microalgae can be used to make protein powder or added to various food products.
• Purple laver (Porphyra) is one of the most commonly farmed marine algae. In Asia, it is used to make nori in Japan and gim in Korea. In Wales, it is used in laverbread, a traditional food. In Ireland, it is boiled to make a jelly. It can also be fried or beaten with water to create a pink jelly. It is also harvested along the west coast of North America, Hawaii, and New Zealand.
• Algae oil is used as a dietary supplement because it contains Omega-3 and Omega-6 fatty acids, which are also found in fish oil and support brain health.
• Dulse (Palmaria palmata) is a red algae sold in Ireland and Atlantic Canada. It is eaten raw, dried, or cooked like spinach.
• Spirulina (Arthrospira platensis) is a blue-green microalgae that has been used as a food source in East Africa and pre-colonial Mexico. It is high in protein and nutrients and is used as a supplement to help with malnutrition. Spirulina grows well in open systems and is cultivated commercially. One of the largest production sites is Lake Texcoco in central Mexico. Spirulina is often used as a nutritional supplement.
• Chlorella, another microalgae, has a similar nutrient profile to Spirulina. It is popular in Japan and used as a supplement that may affect metabolism.
• Irish moss (Chondrus crispus) is a source of carrageenan, which is used to thicken foods like puddings, sauces, and ice cream. It is also used in beer production.
• Sea lettuce (Ulva lactuca) is used in Scotland, where it is added to soups and salads.
• Dabberlocks (Alaria esculenta) is eaten fresh or cooked in Greenland, Iceland, Scotland, and Ireland.
• Aphanizomenon flos-aquae is a type of cyanobacteria similar to Spirulina and used as a nutritional supplement.
• Extracts and oils from algae are used as ingredients in various food products.
• Sargassum species are important seaweeds that contain many phlorotannins.
• Cochayuyo (Durvillaea antarctica) is eaten in salads and ceviche in Peru and Chile.
• Both microalgae and macroalgae are used to make agar, which is used as a gelling agent in foods.

Scientists at Flinders University in Australia are testing ways to use marine microalgae to make proteins for people to eat. They are creating foods like "caviar," vegan burgers, meat substitutes, jams, and spreads. By changing microalgae in the lab, scientists can increase its protein and nutrient content and improve its taste. These foods have a smaller environmental impact than other protein sources because microalgae absorb carbon dioxide instead of releasing it.

Both microalgae and macroalgae are used to make agar.

For many years, seaweed has been used as fertilizer. It is also a good source of potassium for making potash and potassium nitrate. Some microalgae can be used this way too.

With concerns about global warming, scientists are looking for ways to capture carbon dioxide more efficiently. Carbon dioxide from power plants can be used to grow algae in open or closed systems, which helps reduce greenhouse gases. Untreated sewage can also provide nutrients, turning two problems into useful resources.

High-purity carbon dioxide and carbon captured from the atmosphere can be used to help reduce climate change.

Algae farming is being studied for removing uranium and plutonium from the environment and cleaning up fertilizer runoff.

Businesses, schools, and governments are researching ways to use algae to make gasoline, biodiesel, biogas, and other fuels. Algae can be used directly as a biofuel or to produce hydrogen.

Microalgae are also studied for making hydrogen. For example, scientists are testing ways to use microalgae in systems that produce oxygen and hydrogen through photosynthesis.

The BIQ House in Germany, built in 2013, is an experimental building that uses glass panels to grow microalgae. When the panels heat up, the heat can be used to provide warm water for the building. This technology is still new and not yet ready for widespread use.

The Green Power House in Montana, USA, uses a system that combines sunlight and waste wood from a lumber mill to grow algae in eight ponds. Challenges with algae-based systems include the durability of algae panels, the need for maintenance, and high costs.

In 2022, news reports mentioned the development of algae biopanels for energy generation, though their effectiveness is still unclear.

Seaweed grows in shallow and coastal areas and captures a lot of carbon. When seaweed is taken to the deep ocean, the carbon is stored for a long time and does not return to the atmosphere. Growing seaweed offshore and sinking it to the deep ocean could help reduce carbon in the atmosphere. Seaweed grows quickly and can be processed to make biomethane, electricity, or a substitute for

Growing, harvesting, and processing algae

Most growers choose to grow only one type of organism, called monocultural production, and take great care to keep their cultures free from other types. However, scientists are still studying how to prevent unwanted microorganisms from appearing.

When growing mixed cultures, one type of organism often becomes more common over time. If a less common type is valuable, growers need to separate it into a pure culture to grow it. Pure cultures are also important for research.

A common way to get pure cultures is through serial dilution. Growers mix a sample containing the desired algae with filtered water and place small amounts into many containers. After checking the sample under a microscope, they predict that some containers will have only one cell of the desired species. After growing for a while, they use a microscope again to find containers with the right cells to start larger cultures.

Another method uses a special medium that stops other organisms from growing. For example, Dunaliella is a type of algae that grows well in very salty water, which few other organisms can survive in.

Mixed algae cultures can work well for young shellfish. First, seawater is filtered to remove large algae that the larvae cannot eat. Then, nutrients are added, and the water may be aerated. After one or two days in a greenhouse or outside, the mixture is ready for the larvae. This method requires little maintenance.

Water, carbon dioxide, minerals, and light are all important for growing algae. Different algae have different needs. Algae use sunlight, water, and carbon dioxide to create food, a process called autotrophic growth. Some algae can grow without light by using sugars, a process called heterotrophic growth.

Water temperature must stay between 15°C and 35°C to support most algae.

In open ponds, sunlight only reaches the top 3 to 4 inches of water. As algae grow, they block sunlight from reaching deeper layers. Most algae can only use about 1/10 of the sunlight they receive. However, exposing algae to direct sunlight often helps them grow better because the algae below can use the less intense light from the shaded algae above.

To grow algae in deeper water, growers stir the water to move the algae around. Paddle wheels or air from the bottom can lift algae from deeper layers. Stirring also prevents algae from getting too much sunlight.

Another way to provide light is to use glow plates inside the tank. These plates control light intensity and spread it evenly, but they are expensive and rarely used.

The bad smell in wetlands like bogs and swamps can come from oxygen running out due to decaying algae. Without oxygen, bacteria break down algae and create smelly gases like hydrogen sulfide and ammonia. This can harm aquatic life. In carefully managed algae systems, these problems are unlikely to happen.

Some algae and bacteria produce smelly chemicals, like certain cyanobacteria (once called blue-green algae), such as Anabaena. These chemicals, called MIB and geosmin, give water a musty or earthy smell. They are very strong even in tiny amounts and can cause taste and odor issues in drinking water. Cyanobacteria can also produce toxins that harm humans.

Nutrients like nitrogen, phosphorus, and potassium help algae grow. Silica, iron, and other trace elements are also important. Carbon dioxide is needed for fast growth and must be dissolved in water for algae to use.

Seaweed farming involves growing and harvesting seaweed. Some farmers collect seaweed from natural areas, while others control every part of the seaweed's life cycle.

The most farmed seaweed types are Eucheuma, Kappaphycus alvarezii, Gracilaria, Saccharina japonica, Undaria pinnatifida, Pyropia, and Sargassum fusiforme. Eucheuma and K. alvarezii are used for carrageenan, Gracilaria for agar, and others are eaten after processing. Seaweed is different from mangroves and seagrasses because it is a photosynthetic algae and not a flowering plant.

In 2022, China produced the most seaweed (58.62%), followed by Indonesia (28.6%), South Korea (5.09%), and the Philippines (4.19%). Other major producers include North Korea, Japan, Malaysia, Zanzibar, and Chile. Seaweed farming helps improve economies and reduce pressure on fishing.

In 2019, global seaweed production was over 35 million tonnes. North America produced about 23,000 tonnes of wet seaweed. Production in Alaska, Maine, France, and Norway more than doubled since 2018. Seaweed made up 30% of marine aquaculture in 2019. The seaweed extract market was worth $16.5 billion in 2023 and is expected to grow.

Seaweed farming helps reduce carbon dioxide in the atmosphere, making it a good way to fight climate change. Experts recommend more research on seaweed farming to help reduce climate impacts. Organizations like the World Wildlife Fund and The Nature Conservancy support expanding seaweed cultivation.

An open system of algae farming uses shallow water in natural or artificial ponds. These systems are simple and cheap, making them popular for commercial algae production. However, open systems are easy to contaminate with other organisms and cannot control temperature or light well. They are best used in warm areas and during warm seasons. Open ponds are less expensive to build but require more maintenance.

Algal culture collections

Certain types of algae can be obtained from collections that store algae. More than 500 of these collections are listed by the World Federation for Culture Collections.