Microalgae and More: Is Algaculture Our Sustainable Saviour?

With a rising global population, increasing wealth and health awareness, the demand for energy, nutritious food and other resources has become insatiable [1]. The reliance on fossil fuels, throw-away culture and the destruction of the environment to meet human demand are exacerbating climate warming. Current lifestyles common in high-income countries aren’t sustainable in the long term. As a result, research into sustainable alternatives to food and other resources has accelerated to meet UN Sustainable Development Goal (SDG) 13: Climate Action. Algaculture, farming macro and microalgae for use as raw materials in the production of sustainable alternatives, has sparked a particular interest. 

Algae has been used globally in human diets for thousands of years; more recently, it has been commercially used in dietary supplements and added to foods to increase their nutritional value [2]. Current research is increasingly focusing on using algae in sustainable products given its resource efficiency compared to conventional crops (Fig. 1) [3]. Algae typically grow rapidly, producing more biomass per unit area than terrestrial plants, with the ability to capture and store up to 50 times more carbon dioxide [3, 4, 5]. As algal species are predominantly aquatic, they do not compete with crops for arable land [5]. In addition, they do not require freshwater to grow, thereby reducing reliance on water sources when farming, which is particularly important in communities where water is scarce [6]. In addition to algae's sustainable advantages, many species can provide more protein (up to 70% protein content), amino acids, essential fatty acids, antioxidants, vitamins and minerals compared to terrestrial alternatives [4, 7].

Figure 1 - A comparison of the land and freshwater footprints required for the production of essential amino acids from different food sources. Land footprints are reported in hectares per metric ton of product. Freshwater footprints are reported in cubic metres of freshwater per metric ton of product.  Reprinted from Ref [4] under the Creative Commons Attribution 4.0 International License.

Improving Food Security and Combating Malnutrition

Currently, a handful of algal species, like Spirulina, Chlorella and Pyropia (a.k.a. “nori”), are commercially produced for high-value, highly nutritious products [2, 5, 7]. However, it is thought that expanding their production could help sustainably meet future food and resource demands [3, 4]. It is predicted that marine algaculture could even exceed global projected protein demand by 2050 [4].

This expansion could help combat malnutrition in the developing world using less land and water than the equivalent output produced using conventional agriculture. Although unlikely to be a substitute for traditional agricultural products, algae can supplement communities and help to meet the SDG 2: Zero Hunger, without putting further strain on the environment [1]. 

Alongside algae being an excellent source of protein and micronutrients, algaculture could provide jobs and stimulate economic activity in coastal areas [7]. Local farms could provide farmers with reliable income, independent of rising land and fertiliser prices [3]. In addition, with sea temperatures increasing and overfishing pressuring communities that rely on aquaculture, algaculture could be a chance to diversify their income [8]. This has already been seen in Maine where self-employed fishers have started to farm seaweed to reduce their reliance on lobstering and supplement their income whilst supporting the very ecosystem they rely on for their aquaculture industry [8]. 

Minimising Fertiliser Use and Eutrophication

Eutrophication occurs when an overabundance of nutrients in a water body supports the growth of harmful algal blooms on the water's surface [9]. These algal blooms block sunlight and release toxins, damaging the surrounding ecosystem, and their subsequent decomposition depletes dissolved oxygen and causes other species to suffocate [9]. In comparison to terrestrial crops, algae are more fertiliser efficient; the only nutrients lost are those in the harvested product [4]. This minimises fertiliser runoff, limiting the build-up of nutrients in water bodies and preventing the destructive effects of downstream eutrophication [4, 10].

Although algae require nutrients that are typically provided in fertilisers, like nitrogen and phosphorus, to grow, it is suggested that wastewater could be used as an alternative source [3]. Research into using wastewater, which stores high levels of nitrogen and phosphorus, to feed algae is ongoing [11]. This could reduce fertiliser use, costs and runoff.

Intentionally growing algae in waterways polluted by fertiliser runoff has also been proposed to help minimise eutrophication [3, 5]. This strategy can also be applied in polluted waters in urban environments by using algae to filter the wastewater and produce drinkable water for recirculation into local populations [3]. As algae filters the water it can minimise the emissions and use of resources associated with traditional wastewater treatment facilities, whilst also producing algal biomass for other production purposes (Fig. 2) [3]. Further research into this process investigates using algae to bind the nutrients in waterways, reclaiming non-renewable nutrients like phosphorus for future use in traditional agriculture and algaculture (Fig. 2) [3, 10].

Figure 2 -  The marine circular bioeconomy of algaculture. This shows the many ways in which algae can help reuse and recycle products across different sectors. DAC = direct air capture. BECCS = bioenergy with carbon capture and storage. Reprinted from Ref [4] under the Creative Commons Attribution 4.0 International License.

Saving Space and Carbon Sequestration 

Although algae do not require arable land and don’t compete with terrestrial agriculture, they still require growing space. Some algae are grown in coastal waters as potable water is not required [6]. Ongoing trials are also investigating the viability of algae farms further offshore to utilise the massive untapped growing potential of the oceans [12, 13]. Offshore farming could produce large quantities of algal biomass for produce whilst avoiding the use of terrestrial sites [12, 13]. In addition, it could also allow for the establishment of large, undisturbed areas of algae for carbon sequestration, capturing and storing carbon dioxide, to limit climate warming (Fig. 2) [12, 13]. Globally, if conventional agriculture was replaced by algaculture both on and offshore, it could have more impact on the climate crisis through carbon sequestration alone than the production of other sustainable algal products [6]. 

Algal farms may also be erected onshore, using infertile land like coastal deserts, wastewater treatment facilities or using vertical farming technologies on urban rooftops where conventional agriculture would not occur [3]. These techniques will allow increased production to meet nutritional food demands without competing with existing agriculture or requiring further deforestation to make new agricultural space, helping to accomplish SDG 15: Life on Land.

Combating Overfishing

While we can save agricultural resources and space with algaculture, we can also help to alleviate the pressure on the oceans, working to meet SDG 14: Life Below Water. The pressure on ocean ecosystems due to the nutritional demand for fish is severe [14]. However, farming fish as an alternative to ocean fishing is also unsustainable, as aquafeed requires arable land and lower trophic-level fish to produce [14]. The essential omega-3 fatty acids found in the lower trophic level fish used in human supplements and animal feed come from marine algae that they consume [14]. The use of microalgae as a sustainable source of omega-3 in replacement of fish oil tablets and fishmeal is already in production [7, 15]. This substitution reduces the reliance on lower trophic level fish, allowing their populations to recover [15]. Fish at higher trophic levels with declining populations, like tuna, can also benefit from the population recovery of their prey species, thereby maintaining balanced marine ecosystems [15]. The substitution is particularly important to consider as the global population increases, since a further increase in demand for these products is unviable [14, 15]. If microalgae were used globally as an omega-3 substitute for human supplements and fish farms, there could be a 30% reduction in fishing pressure for lower trophic level fish helping marine ecosystems to recover and persist [15]. 

It has been suggested that offshore infrastructure built to support algaculture could provide an artificial habitat for other species, further supporting marine biodiversity [16]. In addition, it has been suggested that farming macroalgae like kelp could also support species by providing habitat similar to their natural counterpart kelp forests [17, 18]. Cultivated  macroalgae may also provide water quality regulation amongst other benefits for marine species [16, 18]. However, threats to existing biodiversity and habitats must also be considered. Algae can alter physicochemical and biological factors which can damage vulnerable environments like coral reefs [16]. There is also threat from the introduction of invasive species, both algae and species it hosts, into novel environments alongside disturbance from the algaculture infrastructure [16, 18]. Risk assessments to evaluate the impact of algaculture infrastructure must be factored in when planning placement and future management [16].

Biofuel and Co-Product Production

With the demand and price for fuel increasing and the unsustainable nature of fossil fuels, biofuel production is one of the biggest areas of research seeking to utilise the sustainable benefits of algae, which will help meet SDG 7: Affordable and Clean Energy [19]. First-generation biofuels, which use terrestrial crops like corn, soy and sugarcane, compete with food crops for arable land [5, 14, 19]. It has also been suggested that using these traditional oil crops for biofuel production cannot meet the current rates of fossil fuel consumption [5]. These issues have led to an investigation into the use of algae for biofuel, with its high productivity and oil content [5, 19]. Many species of algae produce lipids used in the conversion to biodiesel and hydrocarbon fuels [6, 20]. Some species can produce 10-100 times more oil than the food crops currently used in biofuel production [19]. Arable land freed up by using algae instead of first-generation biofuel crops can instead be used to support increasing global food demand. Using algae as a sustainable feedstock to produce biofuel makes the process more sustainable. 

To further improve the sustainability of biofuel production, investigations into recycling waste carbon dioxide and wastewater used to feed algae have been initiated (Fig. 2) [21, 22]. In addition, multiple “algae-derived” products, like carbon-negative construction materials and nutraceuticals, can be produced alongside biofuel in biorefineries, making the process more economically viable and sustainable [5, 6, 22]. For example, protein from residual algal biomass leftover from biofuel production can be used for animal feeds and human consumption, reducing waste. The by-product protein produced when meeting global liquid fuel demands with biofuel could provide ten times the current annual soy protein production globally [6]. In addition, animal feeds produced using this method were shown to have greater nutritional benefits in feed trials, justifying higher market values, and increasing the economic viability of biofuel production plants [15]. High value co- and by-products may allow more competitive biofuel pricing, enabling them to compete with cheaper alternatives like fossil fuels [3, 5, 6]. 

Feasibility 

The billion-dollar question is: can algae be viably used at large commercial scales to support global populations and mitigate climate change? Currently, algae product production is a multi-billion-dollar industry based on small-volume, high-value products, with marketing and packaging adding further value [20]. However, producing sustainable algae products at a larger commercial scale is limited by large investment requirements and high production costs [3, 5, 15]. In addition, the profitability of sustainable products, like renewable fuels, is hard to achieve with bulk production at lower market values given the high costs [5, 22]. Production methods are also under scrutiny due to their energy and resource requirements which contribute to climate warming [22]. Unless sustainable methods such as recycling wastewater and carbon dioxide and the introduction of renewable energy supplies can be applied, whilst still maintaining reasonable cost, production will be unviable [3, 6]. There are also underlying issues with the demand and economic incentives for sustainable products and production methods that may also limit the use of algae as a sustainable alternative globally [3]. 

Although there are issues with the commercial use of algae, laid out above, there are also developments in research attempting to counter these problems. There is ongoing research into manipulating the biochemical composition of algae to tailor species for specific uses [22]. It is hoped that algae can be produced with improved lipid, protein and nutrient content, disease resistance and higher productivity so they can be grown reliably in fluctuating environments at low costs [2, 5, 20]. This research can improve the existing benefits of algae; for example, if engineered algae were to be used to capture phosphorus from wastewater, it could be three times faster and store more of the nutrient than existing algal strains [10]. This development may also allow phosphorus to be reused directly as fertiliser, thus recycling this non-renewable resource [10]. Research into disease resistance and management of pests is critical, considering the increased incidence of algal pond crashes due to pollutants and climate change [23]. 

There must also be development in the processing of these algal products to reduce cost and compete with conventional feeds, fuels and products [5]. The production of high-value co-products in carbon-neutral biorefineries, alongside the economic incentivisation of using algae for wastewater treatment and carbon sequestration, has the potential to support the use of algaculture commercially [3, 6]. Furthermore, suppose trials of algae farms further offshore and in unproductive and urban environments are successful [12, 13]. In that case, space constraints and competition with existing agriculture will be limited, allowing algaculture to support population demands and reduce their environmental impact [3, 4].

Summary

There is additional research and development required before algaculture can become a stable, sustainable provider of global resources and products. However, there are plenty of promising industries and sectors that algae could be used in whilst helping to accomplish several SDGs. Further incorporating algae-derived products into consumer habits, commercial ventures and public initiatives has the potential to supplement diets, combat malnutrition, reduce fertiliser runoff and downstream eutrophication, treat wastewater, and act as a carbon sink. Unlike conventional agriculture, algaculture can utilise infertile and unproductive land. Alongside reducing the pressure of conventional agricultural practices on the environment, algaculture has the potential to relieve the pressure of overfishing by being used as an omega-3 supplement substitute. In addition, the use of algae in biofuel production not only replaces the use of fossil fuels but can also be more sustainable than current biofuel production which uses more land, water and fertiliser than algae would require. Alongside biofuel production, there is potential for the output of a range of coproducts from the same industrial process. 

There are open doors in both local and global online communities for younger generations to contribute to tackling the climate crisis. On a local scale, if individuals or communities started to integrate sustainable products like algal substitutes into their daily lives, it may not only contribute to combatting the climate crisis but also support the industry in making larger contributions in the future. Internationally, young individuals are already stepping up and making changes to influence future climate action through platforms like the UN Economic and Social Council (ECOSOC) Youth Forum [24].  

With its ability to save resources, capture carbon and nutritionally support human populations, algaculture could indeed be the “sustainable saviour” that we need in the future, where demand is at an all-time high and as the climate crisis continues.

References

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