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bullet Bridge DATA Series

Who harvests seaweeds?

Written by: Dr. Carol Hopper Brill and Lisa Ayers Lawrence, Virginia Sea Grant, Virginia Institute of Marine Science

Grade Level:

Lesson Time:
1.5 hr

Materials Required:
Graphing paper ruler, world map

Natl. Science Standards
Click here for a list of the aligned National Science Education Standards.

Related Resources
Algae, Aquaculture, Chemical oceanography, Technology

Using data from the United Nation's Food & Agriculture Organization and TradeDataNet, students will explore harvest and production data of seaweed around the world.


  • Compare the world harvest of different types of seaweed.
  • Evaluate and graph seaweed production harvests.
  • Interpret variation in global seaweed production.

Algae, Phycocolloids, Agar, Alginate, Carrageenan

Seaweed has been traditionally harvested in Europe, Asia and the Pacific Islands for thousands of years, and today harvesting

Seaweed has been traditionally harvested in Europe, Asia and the Pacific Islands for thousands of years, and today harvesting seaweed is big international business. Not only are seaweeds harvested for direct consumption of the plant itself, but also for the intriguing and functional chemicals or "natural products" they produce. Many of these compounds have application for human use. Chemicals derived from seaweeds are used in medicines, food and beauty products, and industry. That's right, the ice cream and chocolate milk in your fridge, the lipstick in your makeup bag, and even the toothpaste you brushed your teeth with this morning may all be made with seaweed extracts.

How does seaweed end up in both whipped topping and paint? Most seaweeds are algae -- aquatic plants that lack roots, stems or leaves. Algae are divided into three main types: red, brown and green. From each of these types of algae, scientists have been able to identify and isolate compounds that can make foods creamier and paint thicker. Red and brown algae produce phycocolloids ("phyco" = seaweed, "colloid" = glue) that include agar, alginate and carrageenan. Green algae produce the antioxidant beta carotene which is a precursor to vitamin A.

The use of these compounds in food products took off in the second half of the 20th century as the demand for prepared foods increased. Compounds like carrageenan improve the quality of the food and help to stabilize it, making the item more appealing to consumers. Currently the import and export of seaweed is a $200 billion business, with the United States importing nearly $50 billion worth each year. And as more nations become developed, the need for more prepared foods and pharmaceuticals will increase the demand for seaweed compounds.

To meet this demand, selected marine algae are grown, harvested and processed on large scales around the globe.  In 2002, farmed seaweed production was 88% of total seaweed supplies (FAO Report).  Progress does have a price tag, however.  Some of the most productive seaweed species have been transplanted outside their natural range. In their new environment, they are "introduced" or "alien" species. Despite the best intentions and efforts of researchers & industry, these species sometimes escape into the wild (through the aquarium trade, aquaculture, ship ballast waters and boat hulls) and have serious ecological impacts. Hawai'i reports problems with invasive algae species and is trying different methods to prune back algae growth affecting coral reefs.

Although seaweed farming is an ancient practice, innovative methods are always being explored. Bridgeport Regional Vocational Aquaculture School in Connecticut has been working with Connecticut Sea Grant researcher Dr. Charles Yarish to improve aquaculture techniques for the red alga, nori (see picture above). Students and scientists are cultivating nori next to salmon aquaculture pens. The red algae remove from the water excess nutrients produced by the fish, and in turn use those nutrients to grow.

Who harvests and imports seaweeds? The activity below will help you answer this question.

Data Activity

We'll start by using the United Nations Food & Agriculture Organization (FAO) statistical site to research fishery production of marine algae around the world. A report by Trade Data International provides charts on countries that import and export algae and the average import prices.

How Much Seaweed Is Produced?

What were reported world seaweed production for the past decade? Using the FAO Stats we can investigate the world productin and dollar value of aquacultured seaweeds.

  • Go to the FAO Global Aquaculture Production page.
  • Under Available Format & Information Products, under Dataset, select Global Aquaculture Production (online query).
  • Select the Species tab.
  • Click on the plus next to Aquatic plants.
  • Check the checkbox next to Brown seaweeds.
  • Click submit.
  • Record the Aquaculture: Quantity & Value data for the past decade.
  • Repeat for Green and Red seaweeds. (Note: To see data combined, check all checkboxes at once).

Looking at the data...

  • What was the production quantity of brown seaweed for the most recent year? Of green seaweed? Of red seaweed?
  • What is the total production of all seaweeds?

  • How has it changed over the last decade?
  • What was the dollar value of of brown seaweed for the most recent year? Of green seaweed? Of red seaweed?
  • What is the total value of all seaweeds?
  • How has it changed over the last decade?

Who Produces Seaweeds?

Next, let's focus on who is producing the seaweed. Looking at FAO data by continent, which continent produces the most brown, green and red seaweeds? How do you think the economy of these regions are impacted by seaweed production?

Who Imports Seaweeds?

Which countries import the most seaweeds? Many countries import seaweeds, including the United States. Use Trade Data International's report to research who buys the most.

  • Make a list of the top 5 seaweed-importing countries in 2001.
  • What was the value of seaweed imports into all countries in 2001? (Use the average import price paid by the top importing countries.)
  • How much seaweed did the US buy in 2001? What proportion of the world's seaweed market did this represent? From which countries does the US buy seaweeds?

Sell Your Seaweed

Visit Ocean Planet’s “There Are Algae in Your House!” page, and use their list of household foods containing seaweed products.  Imagine that you would like to get into the seaweed business and culture seaweed. Pick a type of seaweed that you might grow (red, green, or brown) and determine which food companies might be interested in buying the corresponding byproduct (carrageenans, beta carotene, or alginates) from you. Design a marketing campaign to sell your seaweed byproduct.

Supply and Demand

Supply and demand interactions drive the prices of commodities. Look at the Trade Data charts 10 & 13 of global seaweed imports and average import prices. Describe the relationship between import quantity and price per ton.  Think about what may affect supply of seaweed products and what may affect demand for seaweed products.  Also think about how this affects your paycheck as a seaweed grower.

Seaweed products provide just one example of how chemicals derived from marine organisms have become increasingly important in our lives. The sea's biodiversity and extreme environments continue to attract scientists as they search for new compounds, organisms and biotechnology opportunities. The treasures we can extract from the sea should also heighten our efforts to sustain healthy marine ecosystems.

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