All About Green

The Unlimited Potential of Seaweed Farming

Oct 2023
Author: Green Power
photo from pixabay

Seaweed farming is not a new phenomenon. There is a long-standing history of growing edible seaweed in China. Today, seaweed farms stretch from the waters off Dalian, Liaoning to Nanao, Guangdong, offering a diverse range of species, including kelp (Laminaria sp.), laver (Porphyra sp.), Gracilariopsis lemaneiformis, Undaria pinnatifida, Sargassum fusiforme, and Sargassum thunbergii. As the impacts of climate change lead to increasingly extreme weather events and food crises, countries around the world are working to reduce emissions. Some scientists even believe this culinary delicacy could be a promising solution to these challenges!

Carbon dioxide (CO2) exists not only in the atmosphere but also dissolves in water. There is a constant exchange of CO2 between the atmosphere and the ocean, reaching a dynamic equilibrium known as "air-sea CO2 exchange". In other words, if CO2 in the ocean decreases, more CO2 from the atmosphere will dissolve into the sea. Seaweed absorbs CO2 during photosynthesis. Even though it grows in the ocean and takes in CO2 from there, it indirectly reduces CO2 levels in the atmosphere through the air-sea CO2 exchange. Research estimates that one hectare of seaweed can absorb 300 to 1,800 kilogrammes of CO2 from cultivation to harvest.

The Compounding Benefits of Seaweed

Livestock farming is one of the largest sources of carbon emissions. This is because cattle and sheep emit significant amounts of methane, a greenhouse gas with a higher global warming potential than CO2. Research has shown that ruminant livestock emit less methane when fed with seaweed-supplemented diets. Seaweed is also suitable for human consumption, being rich in protein and fibre. If it can replace vegetables in our diets, it will not only benefit our health but also reduce the need for arable land, indirectly preserving more forests and giving us more trees to store CO2.

Furthermore, seaweed can be used as biofuels. They grow rapidly, require no arable land, and consume far fewer freshwater resources, making them a superior biofuel source compared to maize.

Seaweed farming
Seaweed farming
©Rachel Clara Reedb @ Wikipedia

Careful Site Selection to Minimise Impact

While seaweed offers numerous benefits, careful planning is still necessary. When cultivated in relatively homogeneous marine environments, they can provide an additional microhabitat for organisms, enhancing overall species biodiversity. Conversely, in more complex marine ecosystems (such as coral reefs or seagrass beds), seaweed farming may disrupt the growth of some species like corals and seagrasses, potentially reducing biodiversity.

Significant amounts of nutrients (mostly nitrogen and phosphorus) from the land are transported to coastal estuaries by river streams. If seaweed farms are strategically set up in these areas, these abundant nutrients can be absorbed by seaweed, which is good for their growth. Seaweed can reduce the occurrence of red tides caused by excessive nutrient runoff, which in turn serves to enhance water quality. On the contrary, if seaweed farms are situated outside of estuarine regions, the nutrient supply from river streams can become unstable due to seawater movement. In such cases, additional fertilisers may be required to sustain seaweed growth, potentially leading to marine pollution. As a result, choosing the right location for a seaweed farm is crucial.

Pros and Cons of Artificial Farming

While there are over ten thousand seaweed species in the world, only a handful of them are edible and can be grown using modern agricultural methods. Since seaweed farming activities have always been concentrated in East Asia and Southeast Asia, foreign seaweed species may need to be introduced should there be a demand for large-scale seaweed farming in other regions. However, the escape of these non-native seaweeds from farming sites into the wild can spell trouble. On the one hand, they may compete with native seaweeds for space and nutrients, potentially driving the latter to extinction. On the other hand, hybridisation between non-native and native seaweeds can contaminate the genetic integrity of native populations, leaving irreversible impacts on local marine ecosystems.

Furthermore, deepwater seaweed farming requires the installation of numerous ropes known as "seedling ropes". Marine experts have warned that these seedling ropes, whether vertically or horizontally suspended in the water, have the potential to entangle large marine animals such as whales, dolphins, and sea turtles. In particular, whales instinctively toss and turn when ensnared, causing the ropes to tighten around them and increasing the risk of death.

Hong Kong Possesses Development Potential for Seaweed Farming

Hong Kong is home to 264 seaweed species, including edible native seaweeds like kelp. Situated at the mouth of the Pearl River, Hong Kong's waters are rich in nutrients. Coupled with neighbouring regions possessing seaweed farming expertise, there is potential for the development of a local seaweed farming industry in Hong Kong. However, this endeavour hinges on the careful selection of suitable locations for seaweed farms, with particular emphasis on avoiding dolphin habitats and ecologically sensitive areas.

As for the seaweed harvests of the future, it is anticipated that the primary use will be for consumption, given the current absence of local technology for converting seaweed into biofuels. Consuming seaweed is nothing new for people in Hong Kong. By advancing the concept of substituting vegetables with seaweed, we can reduce our reliance on imported vegetables. This, in turn, can help reduce transportation-related carbon emissions, tackling several issues at once!