An Introduction to Underwater Sea Gardening

By Madelin Jimenez

"I'd like to be, under the sea, in an octopus' garden, in the shade" sung The Beatles back in 1969 and I think they were on to something! Seaweed has been classed as one of the most sustainable food sources in the world and can grow incredibly quickly, with some varieties growing as much as 2ft per day! Dive into the underwater sea garden with me to discover the remarkable power of seaweed.

giant kelp forest
35mm photo of a Macrocystis pyrifera giant kelp forest, taken on Nikonos V.

Seaweed is not a plant? So what is it?

Whilst seaweeds are commonly known as the vegetables of the sea they are not classified as a plant but instead are a part of their very own kingdom, as an algae in the Protista kingdom. Unlike plants, algae do not have roots and take up nutrients directly from the seawater surrounding them. Algae do not have seeds or pollen but rather spores (1). Long ago, blue-green algae (you may know it as the supplement E3 Live) was the first organism to ever photosynthesize (2). Not until ferns came along 3 billion years later did plants on land ever exist - so evolutionarily speaking seaweeds are very old, and we can thank the first algae for creating oxygen on this planet! (3)

What is seaweed used for?

You might be surprised to know that seaweed is in a lot of products we already consume. Many of the compounds of seaweed are extracted and used as a thickening agent for everything from ice cream to toothpaste and face creams (4). Seaweed is found in many popular dishes and is a culturally important ingredient in many regions such as Japan, Philippines, Hawaii, and to the native peoples of the Americas (5, 6). For ocean-going vagabonds like yourselves, seaweed is capable of providing a valuable food source that is readily available, highly nutritious and extremely versatile; adding it to soups, salads, crackers, pickles and even desserts.

What are some common edible seaweed varieties?

Seaweeds have many common names in many different languages, so scientific names are also included below.

1. Nori or Pyropia species are among the most famous of the edible seaweeds. Many of you may be familiar with 'Nori,' used for sushi paper and popular seaweed snacks, this is typically made from Pyropia species. This family of red algae and can be found in the tide pools, hanging off of rocks and has a deep purple-red color that becomes dark green once dried. Pyropia can be roasted and pressed into dry sheets, or it can be cooked down and added to savory dishes.

2. Kombu or Laminaria species are kelps in the family of brown algae, most commonly known for their use in miso soups. Laminaria have stipes- stalk-looking structures that attach themselves to the bottom of the seabed and have thick brown blades. Laminaria grow at depth but can still be found in the deeper edges of the tide pools. Kelps or brown algae, are much thicker and more “gooey” compared to the other families of algae and are best when cooked or marinated. Laminaria can be used to make a savory vegetable-based broth and is amazing in ramen and noodle soups.

3. Wakame, popular in seaweed salad, is known as Alaria marginata on the Pacific coast though other species are used as wakame as well, such as Undaria pinnatifida (which is an invasive algae to many regions such as California and New Zealand). Wakame is a mild, versatile kelp that can be sliced into strips and marinated to make salads, or air dried, chopped up and used for stir-fries. Wakame has a sweet taste and a smooth texture, and is a good source of omega-3 fatty acids.

4. Sea lettuce, or Ulva species are green algae that the grow as very thin bright green blades with a taste comparable to spinach. This is a mild seaweed that is easy to find in shallow tide pools and can be identified by its bright green color. Ulva can be eaten raw, dried, or cooked and is very versatile and has less flavor compared to the more savory seaweeds.

5. Ogo or Gracillaria species are in the family of red algae and look like red, wirey bushels. Gracillaria is a personal favorite to eat and is best enjoyed raw and fresh. It brings a light and crunchy addition to any dish or salad and is becoming increasing trendy on poke bowls.

How do you harvest them?

The best way to forage for seaweed is to get out there and get your hands wet!

Tide pools allow you to forage along the coast where many of the desirable seaweeds grow, but if you dive a little deeper many species can be found in abundance while freediving in the shallows. A great place to start seaweed hunting is in the rocky intertidal zones where you can forage and explore the sea by foot at low tide.

It's best to cut off only the blade and leave the “stipe” or base of a seaweed so it can still regrow. When the ocean gets wild this can be a great opportunity to forage for seaweeds that have been knocked off the sea floor. Since algae do not have “roots,” seaweeds do not necessarily need to be attached to anything to live and photosynthesize, they can continue to live and prosper floating in the waves. Just make sure to harvest seaweed when it is still wet and fresh.

Unlike many other foraged foods, there are currently no known poisonous or toxic seaweeds in existence. There are a few seaweeds that produce acid, but these are no more acidic than your own stomach acid and would not harm you if consumed. It is important, however, to be aware of the water it grows in. You do not want to harvest seaweed if it is growing in contaminated or polluted water such as near a power plant or river mouth due to the risk of ingesting the polluted water. Like land vegetables, it is a good idea to give your seaweed a rinse.

Make sure to pay special attention to where marine protected areas are in your foraging region and what regulations and limits there may be about taking marine life. For example, in California the daily limit for recreational harvesters of marine algae is 10 pounds wet weight and in marine protected areas the harvesting of any marine species is prohibited. (8)

Why is it a sustainable food source?

Seaweed is classified as one of the world’s most sustainable crops, as it requires no fresh water or fertilizer. Furthermore, it directly absorbs dissolved nutrients and carbon dioxide straight from the ocean, making its carbon footprint negative while being able to grow at a very rapid rate (9).

Additionally, harvesting your own seaweed in a sustainable manner means avoiding any unsustainable aquaculture practices. Many of the bright green “seaweed salads” found at supermarkets and in restaurants is Wakame that has been dehydrated and shipped long carbon miles from Asia, only to be rehydrated with green food coloring. There is always the risk that some of these products support seaweed farms that operate without regulations or sustainable practices and have the potential to compete with and destroy native ecosystems such as coral reefs and sea grass beds.

What are the health benefits of eating seaweed?

The health benefits and value of seaweed as food is well known in Eastern and native cultures, but edible seaweed has recently gained more attention in Western society (12). It has been declared a “superfood” and lays claim to being even more nutritious than the all-mighty- Kale. Since seaweed is an alga and not a plant, it contains far more nutrients and minerals than their landlubber competitors - vegetables.

Seaweed has a concentration of minerals with values about ten times higher than traditional vegetables - such as iron in Laminaria in comparison to lentils, or calcium present in Wakame compared with milk. For those who choose a plant-based diet, seaweeds are one of the few ways to naturally consume vitamin B12 and are also a surprisingly good source of high-quality protein, containing all of the essential amino acids. Seaweeds contain many other vitamins and minerals, such as vitamin K, vitamin B, zinc, and also antioxidants which protect your cells. Additionally, seaweeds are one of the best natural sources of iodine, which is an important mineral that helps support the thyroid gland and regulates your metabolism (1).

To start discovering ways that you can incorporate seaweeds into your diet head over to our Foraged Feasts page for recipes including Pickled Bull Kelp by fellow salty contributor Taryn Pickard.

Madelin Jimenez Marine biologist, surfer, diver, and sailor with a passion for exploration. Specializing in phycology (the study of marine plants) and coral reef ecology, Madelin is a scientific diver and researcher with a focus in marine conservation. Madelin is a liveaboard in San Diego and enjoys cruising the California Channel Islands and Mexico on her sailboat Aquarius. After finishing graduate school at Scripps Institution of Oceanography she plans on sailing and surfing around the world while teaching and communicating science from her sailboat.

See more of Madelin


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1. Sahoo, D., & Seckbach, J. (Eds.). (2015). The algae world (Vol. 26). Dordrecht, The Netherlands:: Springer.

2. Tirichine, L., & Bowler, C. (2011). Decoding algal genomes: tracing back the history of photosynthetic life on Earth. The Plant Journal, 66(1), 45-57.

3. Stiller, J. W., Schreiber, J., Yue, J., Guo, H., Ding, Q., & Huang, J. (2014). The evolution of photosynthesis in chromist algae through serial endosymbioses. Nature Communications, 5(1), 1-7.

4. Anis, M., Ahmed, S., & Hasan, M. M. (2017). Algae as nutrition, medicine and cosmetic: the forgotten history, present status and future trends. World Journal of Pharmacy and Pharmaceutical Sciences, 6(6), 1934-1959.

5. Tseng, C. K. (1947). Seaweed resources of North America and their utilization. Economic Botany, 1(1), 69-97.

6. Abbott, Isabella A. "The uses of seaweed as food in Hawaii." Economic Botany 32.4 (1978): 409-412.



9. Mahadevan, K. (2015). Seaweeds: a sustainable food source. In Seaweed sustainability (pp. 347-364). Academic Press.

10. Tiwari, B. K., & Troy, D. J. (2015). Seaweed sustainability–food and nonfood applications. In Seaweed sustainability (pp. 1-6). Academic press.

11. MacArtain, P., Gill, C. I., Brooks, M., Campbell, R., & Rowland, I. R. (2007). Nutritional value of edible seaweeds. Nutrition reviews, 65(12), 535-543.

12. Abbott, Isabella A. "Ethnobotany of seaweeds: clues to uses of seaweeds." Fifteenth International Seaweed Symposium. Springer, Dordrecht, 1996.


Photos courtesy of California Fish and Wildlife, AlgaeBase, and personal photos.

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