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Seaweed Farming: The Future of Our Oceans

Around the world, countries are tackling poor water quality. However, coupled with the lack of awareness of climate change's effects on water, new technologies have not been able to safely tackle the plethora of problems related to water, the most abundant and important natural resource. This has left many communities in desperate situations to find more accessible, affordable, and efficient oceanic solutions.


One solution that has recently been adopted globally is… seaweed! Seaweed’s versatility as food and other applications, and simultaneously restoring the environment, while being affordable, low-maintenance, and effective, has made it very appealing (Visch et al., 2020).


But, before we dive deep into the benefits of seaweed and the hype around such initiatives, what is the problem? Well, Earth is over 70% water, however, water quality, both fresh and salt, around the world is disintegrating, coupled with our growing population’s growing demand for food, recreational activities, and economic income. Specifically, ocean acidification is a growing concern. With oceans being the largest carbon sinks, the increasing concentration of carbon in water also changes the composition of water. This process is illustrated in the diagram below.


When carbon dioxide is absorbed by the ocean from the atmosphere, the chemistry of the seawater is changed (NOAA, 2020).


Although this process is natural, excessive greenhouse gas emissions – endorsed by the rise of capitalism and urbanization in the last century – have amplified the effect. Due to anthropogenic climate change, the level of carbon dioxide in the atmosphere is increasing the amount of CO2 that is being absorbed by bodies of water. When CO2 dissolves in water, it forms carbonic acid (H2CO3), which is a weak acid that dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3-) (NOAA, 2020). Bicarbonate ions can further dissociate into more hydrogen ions and carbonate ions (Barker and Ridgwell, 2012). The increasing concentration of hydrogen ions is what makes water more acidic; the equation for pH is

-log10[H+].


What is pH?

pH is a scale used to identify the acidity of a substance. The general acidity of oceans is 8.1.


Ocean acidification has resulted in a change in pH by 10-times. It is also important to acknowledge that salt water is a natural buffer, mitigating the acidification process, and with increasing global water temperatures, CO2 can dissolve more easily in water. For this reason, a small change in the ocean indicates tremendous carbon dioxide input. Furthermore, runoff pollutants from land are contributing to the decreasing quality of water.


What is Seaweed Farming?

Seaweed farming may come in different forms, but involves the cultivation, production, and consumption of the plant. The images below illustrate the different structures of seaweed farms. The farm is typically anchored to the water floor and is suspended around 1-2 m below the surface, but there are also small differences with each of the designs (Visch et al., 2020). In most cases, these farms are located near the ocean shores and require sufficient water flow and no fertilizer source.



There are three main types of seaweed: green, brown and red. Different species of seaweed have varying reactions to water quality. With the diversity of seaweed species, the ability to start and encourage aquaculture is possible in many regions.


However, with different water considerations, and environments, the management of these farms would be different. The whole purpose of seaweed farming is to restore coastal-ocean health. Through photosynthesis and/or bioremediation, the growing process of seaweed absorbs the excess and negative nutrients like carbon, nitrogen, phosphorus, and even ammonium. By restoring balance in water quality, seaweed farming can also provide numerous linked benefits.



Benefits of Seaweed Farming:


1. Increase biological and ecological complexity.

a. Growing seaweed can cultivate more habitats, thus supporting biodiversity and the interaction between different aquatic organisms. There are different forms of interactions that can develop with the help of seaweeds, like an increased food source (Hasselström et al., 2018).

b. As a primary producer, seaweed absorbs inorganic matter and carbon, from the water they reside in, to perform photosynthesis (Longton et al., 2019). Through photosynthesis, they are able to produce organic matter, which is a source of energy and nutrients for other organisms. In a study performed by Radulovich et al., growing tropical seaweed on the Caribbean and Pacific coasts of Costa Rica increased the biodiversity of fish and other invertebrates (Radulovich et al., 2015). Many of the aquatic organisms were found to be feeding off the seaweed, while others used it as a form of shelter (Longton et al., 2019).


2. Mitigate eutrophication:

a. Eutrophication is a problem that involves the excessive growth of plants and algae due to the increased availability of various factors that are needed to perform photosynthesis (Chislock et al., 2013). So, this might include carbon dioxide, sunlight, and the elements in nutrient fertilizers, such as carbon dioxide, phosphorus, nitrogen, etc. The consequence of excessive plant and algae growth in water is the lack of control during the decaying process of each organism. When algae blooms decay, it utilizes the oxygen in the water, causing it to deplete (Chislock et al., 2013). This situation is also called dead zones, where an aquatic area is lacking enough oxygen to support the other organisms in the environment (Chislock et al., 2013).

b. Seaweed can mitigate eutrophication by absorbing/uptaking nutrients as it grows (Visch et al., 2020: Seghetta et al., 2016).

c. Based on the study and analysis done by Zheng et al., seaweed aquaculture can remove about 5.56% of nitrogen and 39.60% of phosphorus from the coastal waters in China (Zheng et al., 2022; Xiao et al., 2017). After analyzing numerous farms along the east coast of China, it is also concluded that the type of seaweed and the coastal environment can change the variety of the remediation capabilities seaweeds can provide (Zheng et al., 2022). Similarly, the size of the farm and the production level can influence the type of influences in the environment. With a larger farm and greater diversity of seaweed cultivation, the capability of sequestration of specific nutrients is more abundant.


3. Human benefits:

a. With cleaner coastal waters and a more ecological diverse environment, human health will improve. Clean water is not only good for drinking but is also related to clean air and a healthier environment on land, supporting the health of other animals and organisms. Additionally, iodine is a nutrient that is abundant in seaweed species like Laminaria (Zheng et al., 2022). Safe consumption of iodine is essential for better human health, but can also be beneficial to other plants and animals, and their production. There are other health and economic benefits seaweeds can provide to only name a few.



Challenges and Limitations:


Despite the long-winded list of benefits seaweed farming has, there are, like for any initiative, concerns.


1. Alterations to aquatic environments:

a. Shading: Due to its large size and the likelihood of being produced near the surface of the water, this may lead to consequences like blocking sunlight for organisms underneath. Without sunlight, some organisms may not be able to thrive, leading to unpredicted biodiversity loss (Visch et al., 2020).

b. Water currents: seaweed farming has the ability to slow water motion, reducing the nutrient flow, which may be essential for other aquatic plants and animals.

c. Nutrient battle: Although it is said that seaweed farming does not require any fertilization, this is based on the assumption that there is sufficient (even excess) nutrients in the water. However, by simply introducing a new organism, especially with the purpose of cultivating it, seaweed farming might result in organisms competing for nutrients.


2. Effects on genetics:

a. With different genetic interactions, the introduction of non-native seaweed species may impact the other organisms that share the same space (Zheng et al., 2022). The concerns of invasive species are also growing, and by encouraging seaweed farming in locations where it is just not feasible, can create more problems than solve them.


3. Lack of research

a. Most research done to analyze the role seaweed might play in “absorbing nutrients” is done in a controlled laboratory environment. This might pose difficulties since laboratory settings are different compared to real bodies of water (Hasselström et al., 2018). The effects of sediment retention, for example, still require additional studying in order to identify the challenges that might occur with large-scale seaweed farming in one specific site (Hasselström et al., 2018).


4. Cultural and social barriers;

a. One reason why most seaweed farming research has been done in Asian countries is because of the cultural acceptance and demand (Makame et al., 2021). With the lack of social demand for seaweed farming, the knowledge and support to maintain one would be limited. For example, if it is uncommon to eat seaweed and/or use it for agricultural purposes, this means that the consumption is relatively low. If this is the case, without sufficient demand, there is a small chance that seaweed farming can be done on a larger scale.


Seaweed farming is also not the solution to decreasing water quality. In other words, it is not a systemic solution. Some might even say that this solution is a band-aid solution, hiding the true source of the problem. However, this saying is not wrong. Seaweed farming has the ability to mitigate and hide the extreme effects of our current actions that lead to decreased water quality. If nothing is done to identify and switch our current actions to become more sustainable, poor water quality will always be a problem.



Next Steps:

Though there are numerous concerns with seaweed farming, the environmental benefits that can result from this new practice are considerable. With the ability to absorb large quantities of nutrients from the water, seaweed farming has the ability to mitigate extreme outcomes of eutrophication. The demand and industry for seaweed farming in North America may be small, but with a growing economic interest in sustainable agriculture and consumption, the development will only increase.


Seaweed farming can bring benefits to the environment and economy, giving ever more reason to look forward to the improvements it can provide. Its ability to restore water qualities, being a sustainable food source, and providing a more sustainable alternative to fossil fuels and synthesized fertilizers, seaweed might play a bigger role in the world’s path to becoming more environmentally friendly than we think.



Case Study: Video about Seaweed Farming in Maine



References:

Barker, S., & Ridgwell, A. (2012). Ocean Acidification. Nature Education Knowledge, 3(10), 21. https://www.nature.com/scitable/knowledge/library/ocean-acidification-25822734/


Chislock, M. F., Doster, E., Zitomer, R. A., & Wilson, A. E. (2013). Eutrophication: Causes, Consequences, and Controls in Aquatic Ecosystems. Nature Education Knowledge, 4(4), 10. https://www.nature.com/scitable/knowledge/library/eutrophication-causes-consequences-and-controls-in-aquatic-102364466/


Hasselström, L., Visch, W., Gröndahl, F., Nylund, G. M., & Pavia, H. (2018). The impact of seaweed cultivation on ecosystem services - a case study from the west coast of Sweden. Marine Pollution Bulletin, 133, pp. 53-64. https://doi.org/10.1016/j.marpolbul.2018.05.005


Langton, R., Augyte, S., Price, N., Forster, J., Noji, T., Grebe, G., St. Gelais, A., & Byron, C. J. (2019). An Ecosystem Approach to the Culture of Seaweed. NOAA Tech. Memo, 30. https://spo.nmfs.noaa.gov/sites/default/files/TMSPO195.pdf


Makame, M. O., & Filho, W. L. (2021). Coping with and Adapting to Climate and Non-climate Stressors Within the Small-Scale Farming, Fishing and Seaweed Growing Sectors, Zanzibar. Research Square, 26. http://dx.doi.org/10.21203/rs.3.rs-1083174/v1


NOAA. (2020, April 1). Ocean acidification. National Oceanic and Atmospheric Administration. https://www.noaa.gov/education/resource-collections/ocean-coasts/ocean-acidification


Seghetta, M., Tørring, D., Bruhn, A., & Thomsen, M. (2016). Bioextraction potential of seaweed in Denmark -- An instrument of circular nutrient management. Science of The Total Environment, 563-56, pp. 513-529. https://doi.org/10.1016/j.scitotenv.2016.04.010


Radulovich, R., Umanzor, S., Cabrera, R., & Mata, R. (2015). Tropical seaweeds for human food, their cultivation and its effect on biodiversity enrichment. Aquaculture, 436, pp. 40-46. https://doi.org/10.1016/j.aquaculture.2014.10.032


Visch, W., Kononets, M., Hall, P. O.J., Nylund, G. M., & Pavia, H. (2020). Environmental impact of kelp (Saccharina latissima) aquaculture. Marine Pollution Bulletin, 155(110962). https://doi.org/10.1016/j.marpolbul.2020.110962


Xiao, X., Agusti, S., Lin, F., Li, K., Pan, Y., Yu, Y., Zheng, Y., Wu, J., & Duarte, C. M. (2017). Nutrient Removal from Chinese coastal waters by large-scale seaweed aquaculture. Scientific Reports, 7(46613). https://doi.org/10.1038/srep46613


Zheng, Y., Jin, R., Zhang, X., Wang, Q., & Wu, J. (2019). The considerable environmental benefits of seaweed aquaculture in China. Stochastic Environmental Research and Risk Assessment, 33(5). https://link.springer.com/article/10.1007/s00477-019-01685-z




References to Images:

C.A Goudey and Associates. (2013) A pictorial of a catenary kelp farm (National Fish and Wildlife Foundation, Using Seaweed (Kelp) to Bioextract Pollution (CT)), pp. 22, fig. 8. [Image] URL: https://www.nfwf.org/sites/default/files/finalreports1/1401.13.039525-final_report.pdf


NOAA. (2020, April 1). Ocean acidification. National Oceanic and Atmospheric Administration. https://www.noaa.gov/education/resource-collections/ocean-coasts/ocean-acidification


Peteiro, C., Sánchez, N., & Martinez, B. (2016). Mariculture of the Asian kelp Undaria pinnatifida and the native kelp Saccharina latissima along the Atlantic coast of Southern Europe: An overview. Algal Research, 15, 9-23. URL: https://doi.org/10.1016/j.algal.2016.01.012



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