Seaweeds Promote Cleaner, More Sustainable Aquaculture
Published on Sep 5, 2018

Humans have enjoyed seaweed as a food source in their diet for thousands of years. Several Asian countries, including China, Japan, and Korea, have a history of using seaweed throughout their culinary recipes. Seaweed continues to grow in popularity in western countries, as well. According to The Seaweed Site, more than 21 species of seaweed are used in everyday in Japanese cooking, and seaweed accounted for more than 10% of the Japanese diet until relatively recently.

Seaweed could be a crucial key to developing more sustainable aquaculture.

Although not often discussed, seaweed plays a critical role in the aquaculture industry. According to the United Nations' yearly report on the state of aquaculture from 2018, global aquaculture production in 2016 included 30.1 million metric tons of aquatic plants -- a steady year-over-year increase since 1990. In addition, aquatic plant farming, mostly seaweeds, is now practiced in about 50 countries worldwide. Seaweed provides a healthy, environmentally-friendly food option, and is expected to grow in popularity as a food worldwide in coming years. The new tagline "Kelp is the New Kale” is just one of the ways marketers are promoting and increasing sales of this nutrient-rich product to health conscious consumers.

Growth of aquaculture worldwide over the past 26 years. Image courtesy of FAO of the UN.

But seaweed is more than a source of nutrients for human consumption. Growing seaweed promotes sustainability in a number of surprising and important ways. As aquaculture continues to mature as an industry, growing seaweed looks promising as a method for improving water quality as well as a source of sustainable energy and a natural additive. Here are just a few ways global aquatic plant production is contributing to sustainability in fish farming and other industries.

Improved Water Quality Near Seaweed Production Sites

Seaweed is a safe, natural solution to improving water composition, especially near agricultural sites where runoff from fertilizer and other chemicals can be significant and damaging to the environment. On the coast of Maine, for example, aquaculture experts have nurtured the seaweed industry, with 38 of the 54 U.S. commercial seaweed farms located there. Frequent rainfalls wash excess nutrients, freshwater and pollutants off the land, raising the acidity in coastal waters, which could be harmful for other marine life. But seaweed absorbs nitrogen and carbon dioxide from the surrounding water – a theory known as the “halo effect.

Dr. Nichole Price is a researcher in the area studying aquaculture with farmed shellfish and seaweed. Her research has indicated the potential for calcification of farmed shellfish may be as great as 25 percent higher inside a seaweed farm compared to the outlook for producing shells outside the farm. Farmers and researchers like Dr. Price are working on balancing seaweed cultivation with mussel, scallop or oyster aquaculture to mitigate ocean acidification, add income from the seaweed crop and improve the overall quality of the surrounding water.

Image courtesy of Bigelow Laboratory for Ocean Sciences and the Island Institute.

Wastewater Treatment for Fish Farms

Some seaweeds can absorb heavy metal pollution, including zinc and cadmium from polluted water. The effluent water from fish farms usually contains high levels of waste that can be harmful to other aquatic life in nearby waters. Seaweeds can often use much of this waste material as nutrient. Researchers have launched trials to farm seaweed in areas adjacent to fish farms in order to mitigate pollution issues.

A Source for Biofuels

Kelp, which is a kind of seaweed, can be processed into biofuel by thermochemical liquefaction, wherein the plants are dried out, and rinsed of all the ocean salt before running them through a high-temperature, high-pressure conversion process that transforms it into bio-oil. Although research and scaling these processes is still preliminary, initial reports are promising that kelp may be able to provide at least some percentage of the world's biofuels.

Although seaweed doesn't generally make the top ten list of hot aquaculture topics, there's a lot of potential for this aquatic plant to be a strategic tool for sustainability for aquaculture as a whole - all while delivering greener farming practices and cleaner water.