Course:CONS200/2025FL1/Underwater Agriculture: Exploring the Future of Sustainable Underwater Farming

Seaweed farming

Introduction

Underwater agriculture is basically growing food in shallow water instead of on land. There are multiple different methods for people to grow food underwater. The two main methods for underwater agriculture that are used today are seaweed farming and underwater gardens. Both of these methods are used as well as showing how humans are learning to use the ocean to grow food while protecting the environment at the same time.

Seaweed farming is a common underwater agriculture. By attaching seaweed to a rope or a net that is suspended underwater, it lets the seaweed grow in its natural form. The seaweed will absorb carbon dioxide as well as releasing oxygen, helping to clean the water and fight against climate change. Seaweed can be used for different purposes for example, food for humans, food for animals, fertilizers, and it even provides a hideout for small fishes and other aquatic animals, increasing biodiversity. Since seaweed doesn’t need freshwater, soil, or fertilizer, it is really easy to take care of and it's a safe way to produce food and resources.

An underwater garden involves using small, air filled greenhouses that are attached to the bottom of the seafloor. Inside these small greenhouses, the environment is controlled so we can provide a safe environment for the crops to grow. Farmers can grow land plants like lettuce and berries in these underwater greenhouses. These underwater gardens show that now we are able to grow food in places we once thought was impossible.

Underwater agriculture was able to help reduce pressure on farmland, save fresh drinking water, as well as lowering greenhouse gas emissions. There are also some downsides for underwater agriculture such as, the equipment that are made of metal or plastic can cause pollution in the ocean if it is not managed properly. Large seaweed farms may affect habitats by blocking light levels and water flow.

In order to make underwater agriculture successful, scientists and farmers must have put a second thought on the costs, design, and management. Overall, underwater agriculture shows eco-friendly ways to produce food and fight against climate change.

Nemo's Garden

Underwater Agriculture Methods and Technologies

There are many methods used to practice underwater agriculture from seaweed farming to finding ways to grow common land plants underwater. One common method uses underwater greenhouses, dome-shaped structures anchored to the sea floor for plants to grow in controlled, air filled environments . These systems use sunlight filtered through the water and recycled fresh water from condensation to create a self-sustaining environment for growing . Another method is hydroponic farming underwater, where plants grow without the need for soil, absorbing nutrients from water enriched minerals. These setups are normally powered with renewable energy such as solar panels floating above the water.

Other farming methods include the use of aquaponic systems that merge fish farming with plant cultivation. The fish produce waste that act as natural fertilizer for the plants, while the plants help with water purification . Seaweed and shellfish farming are also part of this broader field, contributing to food production and environmental restoration . Underwater agriculture is a useful and innovative technique to help challenge issues like land scarcity, climate change, and freshwater shortages all around the world while exploring sustainable ways to grow food in marine settings.

The first large-scale underwater agriculture, Nemo’s Garden, uses a hydroponic style of farming. Hydroponic farming is farming without the use of soil, instead it is the method of using a nutrient-rich-film for the plants to grow in. Nemo’s garden uses biospheres, an underwater greenhouse with an artificially created environment ideal for plant growth. It creates this environment with a mix of increasing the atmospheric pressure and using the greenhouse effect to heat up the seawater to evaporate to then become fresh water through condensation, which is then collected and mixed with fertilizer to be used throughout the biosphere for the plants. With this created environment it is shown that the plants grown here have faster growth times and a higher concentration of nutrients making them have a more distinct and intense flavour as compared to those grown on land .

There is also the method of seaweed farming. When farming seaweed there are many different species that can be farmed, such as dulse, bull kelp, ribbon kelp, and sugar kelp. Seaweed farming has a wide range of uses, for example, seaweed is used in cooking, farming, and cosmetics. Seaweed also uses carbon dioxide in the water to grow, in turn helping fight climate change by helping stop ocean acidification. One of the ways seaweed is farmed is by leaving a longline (a long rope or cable) in the water at around 4-8 feet deep and leaving it in the water during winter, when spring comes along it it taken out and by this point the seaweed will have grown to 10 feet or longer. In Alaska, United States alone there was a 200% increase in farming sugar, ribbon, and bull kelp from 2017 to 2019. This growth could help tackle the food shortage in the world as well as help push back against climate change .

Benefits of Underwater Agriculture

Underwater Agriculture is an innovative and sustainable farming technique that offers numerous ecological benefits to the surrounding environment. One of its most significant benefits includes the ability to regulate and enhance the surrounding marine environment. Seaweeds, which are frequently cultivated in aquaculture systems, are well-known regulators of the marine environment . They filter the farming environment by absorbing excess carbon, nitrogen, and phosphorus, helping maintain a healthy balance. It holds the potential to remove significant amounts of nitrogen and phosphorus from the water column it inhabits, supporting marine health .

Bivalves are another key component of underwater agriculture as they serve as filter feeders. These filter feeders help remove particulate matter, also known as particle pollution, from the water, enhancing water quality and clarity . Furthermore, filter-feeders play a vital role in converting nitrogen through denitrification. This process involves converting nitrogen into non-bioavailable gases, as living organisms cannot convert it themselves . Additionally, as bivalves feed and grow, they deposit their waste on the seafloor, contributing to sediment formation .

The physical structures of seaweed and bivalves contribute to stabilizing sediment by reducing water movement, waves, and current velocity . These effects can effectively combat erosion and sediment suspension, which negatively impact marine ecosystems by reducing water clarity and light penetration .

Underwater agriculture also supports underwater life by creating habitats for a diverse range of marine species within and around the farming environment . Another advantage is increased food availability as the presence of bivalves and seaweeds increases this availability . By providing a haven and food availability for marine species, underwater farming supports biodiversity for and around the cultivated area.

Underwater agriculture also stands out as a self-sustaining system. It requires no additional freshwater during the farming process .  This feature makes it an appealing farming method for those with limited access to freshwater bodies. Due to relatively stable seawater temperature, it can be sustained year-round, providing consistent production .  However, with climate change, this can become an issue in the future as water temperatures alter .

Underwater seaweed cultivation could expand in remote coastal communities . In British Columbia, most of these developments will occur in Indigenous territories, which will greatly benefit rather than negatively impact Indigenous communities. A few benefits include enhanced water quality, communities, and rights .

Overall, underwater agriculture is a sustainable, ecologically beneficial farming method for future food systems.

Disadvantages of Underwater Agriculture

Underwater farms present several challenges, many of which become more pronounced as operations scale up. However, large-scale production for underwater agriculture has raised questions about ecological and economic feasibility, logistics, and costs . One of the challenges includes light limitation. On a larger production scale, underwater farms may create excess shading, effectively reducing the amount of light that penetrates the water . It prevents light from reaching the seafloor and the water column. In turn, this affects the growth and productivity of planktonic communities and increases competition for light between cultivated and native species .

Although seaweeds absorb excess nutrients, large-scale production of underwater agriculture may contribute to an influx of nutrients in the environment and is often associated with an increase in harmful algal blooms . These algal blooms can have negative and disruptive impacts on coastal ecosystems, as they disrupt marine food webs and reduce oxygen levels .

As discussed before, marine agriculture can affect the waves and current velocity. This can negatively impact the underwater ecosystem as it reduces the flow of nutrients. The reduction in nutrient flow further disrupts the water exchange needed to maintain nutrient levels for growth . Changes in hydrodynamics can alter local nutrient availability and oxygen levels, negatively affecting the cultivation site and surrounding marine environments .

Additionally, underwater agricultural sites result in increased traffic and machinery for site activities, which can produce noise that negatively impacts marine species .  This can cause behavioral responses that lead to population declines of various marine species in sensitive locations .

Another disadvantage is the release of organic material in the form of particulate or dissolved organic matter, POM and DOM, respectively, due to a combination of wave action and plant tissue matter . This results in the suspension of the decomposed plant matter before it settles on the seafloor. Although studies suggest the release of POM would remain seasonal on a large-scale farming site, the release of POM and DOM remains negatively impactful to the seafloor and its communities .  This is due to large amounts of material decomposition causing sedimentary anoxia and hypoxia, areas with no or low oxygen levels, respectively . Areas where anoxia and hypoxia are prevalent are detrimental to marine life and alter nutrient levels in the marine environment, leading to significant ecological shifts .

The increasing presence of diseases and pests affecting underwater agriculture worldwide is a significant concern. Unlike agricultural activities on land, crops cannot be treated with pesticides and fertilizers, or with a reduction in genetic diversity in sea species . This can result in significant production losses where these diseases and pests are prevalent. It also affects the populations of flora and fauna around these sites due to the diseases .

The intentional or unintentional introduction of non-native species into the environment through farming activities can cause ecological damage . These species can be challenging to eradicate and may become invasive if left unchecked. These invasive species may also venture out and impact neighboring ecosystems .

Current Remedial Actions

Right now there are several underwater agriculture projects and experiments being studied to assess their feasibility and effectiveness. Nemo’s Garden in Italy uses underwater greenhouses, which are transparent domes anchored below sea level. Research shows that even with reduced sunlight underwater, plants can receive enough photosynthetically active radiation to grow. Inside these domes, water from seawater evaporates and condenses to irrigate the plants, demonstrating a method for producing freshwater without soil or additional water sources.

Seaweed and kelp farming is one of the most studied forms of marine agriculture. Peer-reviewed studies from China indicate that large-scale seaweed farms can remove substantial amounts of nitrogen and phosphorus from coastal waters, reducing nutrient pollution and eutrophication. Estimates suggest that cultivated seaweed annually removes tens of thousands of tonnes of nitrogen and phosphorus from Chinese coastal regions. Other research has quantified the carbon sequestration potential of cultivated seaweeds, showing that biomass production captures significant amounts of carbon, nitrogen, and phosphorus from the water.Localized studies have also documented improvements in water quality near seaweed farms, including reductions in dissolved inorganic nutrients and suspended solids.

Current peer-reviewed research shows that underwater agriculture can successfully grow plants under controlled light conditions, produce freshwater through condensation, and offer environmental benefits like removing excess nutrients from the water and capturing carbon. These findings give a solid, science-based foundation for underwater farming. Claims about feeding large populations, replacing traditional land-based agriculture, or being adopted on a global scale haven’t been demonstrated in peer-reviewed studies, so they’ve been left out here.

Future Directions

In the future, underwater agriculture could become an important part of how we deal with food insecurity and climate change, but it’ll need a lot of teamwork and careful planning. Scientists, engineers, and farmers need to keep working on better materials and designs so the farms don’t pollute or break down in the ocean. Governments could help by setting clear environmental guidelines and offering funding for sustainable designs. If communities near the coast are involved in these projects, it can also help create new jobs while protecting local waters. Education and awareness are key too; more people need to understand that oceans aren’t just for fishing, they can be used responsibly to grow food. If managed well, underwater farming could become a safe, eco-friendly way to feed people while taking pressure off land and freshwater systems.

At the same time, underwater agriculture gives us a chance to experiment with ways of growing food that aren’t possible on land. Researchers can learn which crops grow best under water, how to recycle water efficiently, and how to limit energy use. Over time, these lessons could make the farms more productive and sustainable while also protecting marine life. It’s not a quick fix, but careful development now could turn underwater farming into a practical tool for feeding people and supporting healthy oceans in the years ahead.

Conclusion

Underwater agriculture is a new approach, showing how humans are trying to work with the ocean in order to create a better way to grow food, while also supporting the environment at the same time. Through a variety of methods like seaweed farming and underwater greenhouses, researchers had discovered that land isn't just the only place to provide food, and that ocean can provide those opportunities as well. This new method of growing crops helps reduce the pressure on the farmland, save more freshwater, and help restore ecosystems as well.

Overall, underwater agriculture is still in the early stages, but it offers a promising way to grow food while protecting the environment. By combining careful research, sustainable practices, and community involvement, it could provide new sources of food, reduce stress levels on land and freshwater systems, and support healthier marine ecosystems. While it won't replace traditional farming anytime soon, it shows how innovation and science can open up new possibilities for feeding people responsibly and adapting to a changing climate.

References

This conservation resource was created by Course:CONS200.