Seaweed farming

Seaweed farming, also known as kelp farming, is the practice of cultivating and harvesting various types of seaweed.

Unlike land plants, seaweeds are photosynthetic algal organisms that do not produce flowers. This distinguishes them from other marine plants like mangroves or seagrasses. This industry is vital for global economies and environmental health. It provides food, industrial ingredients, and potential solutions for climate change.

Farmers use different methods to manage the seaweed life cycle. In the Philippines, an "off-bottom" method is common in shallow water. Farmers tie seedlings to monofilament lines, which are then strung between stakes in the substrate. In deeper waters, farmers use long-line cultivation. These floating lines are anchored to the ocean floor.

In North Sulawesi, Indonesia, these anchored long-lines are widely used for species like Saccharina and Gracilaria. While much of this work is currently low-technology and labor-intensive, researchers are exploring the use of Remotely Operated Vehicles (ROVs). These robots could install helical anchors to expand farming into unprotected, deeper waters.

Different seaweed species are grown for very specific purposes. The seven most cultivated taxa include Eucheuma spp., Kappaphycus alvarezii, Gracilaria spp., Saccharina japonica, Undaria pinnatifida, Pyropia spp., and Sargassum fusiforme. Species like Eucheuma and Kappaphycus alvarezii are highly valued for producing carrageenan, a gelling agent. Gracilaria is farmed specifically for agar. Other varieties are harvested for direct human consumption after limited processing.

This variety of use drives a massive global market. In 2023, the global seaweed extract market was valued at $16.5 billion.

History shows that humans have interacted with seaweed since the Neolithic period. Seaweed farming began in Tokyo Bay, Japan, as early as 1670. Early Japanese farmers would throw bamboo branches into shallow, muddy water. They waited for seaweed spores to collect on these branches before moving them to river estuaries.

In the 1940s, Japanese farmers improved production by using synthetic nets tied to bamboo poles. This innovation effectively doubled their output. Later, in the 1950s, commercial cultivation of sea grapes (Caulerpa lentillifera) was pioneered in Cebu, Philippines.

The economic impact of seaweed is significant across many nations. As of 2022, China led global production at 58.62%, followed by Indonesia at 28.6%. South Korea and the Philippines also maintain large shares of the market. In Indonesia, seaweed farming accounts for 40% of the national fisheries output and employs roughly one million people. In Tanzania, the industry is a major source of foreign currency. Notably, 90% of seaweed farmers in Tanzania are women.

In Japan, the annual production of nori alone reaches US$2 billion.

Seaweed farming also plays a critical role in climate change mitigation. It is considered a carbon negative crop because it absorbs carbon dioxide. Commercially harvested seaweeds remove about 0.7 million tonnes of carbon from the sea every year. Some species, like the giant kelp (Macrocystis pyrifera), grow incredibly fast. It can grow as much as a day's worth of length in a single day. Some studies suggest that if 9% of the world's oceans were covered in kelp, it could remove 53 billion tons of CO2 per year. This process is part of "blue carbon" sequestration, where seaweed detritus moves to the deep ocean.

However, farmers must manage ecological risks to ensure sustainability. If farmers cut down mangroves to use as stakes, they can reduce water quality and biodiversity. Farming on top of seagrass meadows can also cause environmental damage. There is also a biosecurity risk regarding the introduction of invasive species. Because of this, regions like the UK and British Columbia only allow native seaweed varieties. When managed well, however, seaweed farms can provide habitat for marine life and help protect coral reefs. They can even assist in nutrient bioextraction, which removes excess nitrogen from the water.