Seaweed Harvesting

In the Spring time I head out of Portland, Oregon and drive a couple hours to the coast to gather seaweeds.  Sometimes known as “sea vegetables”, they are actually a form of macro algae and are divided up into three main categories- brown, red and green algae.  They are highly nutritious and have long been prized by coastal peoples throughout the world for their culinary and medicinal properties.  While across the Pacific in Japan and China they are commonly consumed as part of a daily diet, seaweeds are far less consumed here in the States.  We mainly eat seaweed at Japanese restaurants (think nori, miso and seaweed and seaweed salads) and are starting to turn onto seaweed snacks (nori in a salt/oil brine).

This nutritious form of food is abundantly available to us and in Oregon we are allowed to harvest from March through June as much as 2000 pounds of seaweed without a lease.   That is an absurd amount of course but even just a pound or two a year would supplement most of us adequately.  I am by no means an expert on seaweeds but I do know a handful that I come back to again and again for their nutritious and medicinal qualities.  I turn these seaweeds into powders, flakes and strips for broths, soups, smoothies, capsule supplementation and baked snacks that are wonderfully nutrient dense.

Lets take a look at the basics of seaweeds.  They can be divided up into three main categories (Brown, Green and Red) based loosely on appearance due to different pigmentation, cell wall composition and chloroplast structure.   I rely on harvesting about 6 seaweeds from here and I’ll go through each one.


Brown  (Phaeophyta)


Think of brown seaweeds as often the largest ones such as Giant kelp (Macrocystis pyrifera)  Bull Kelp (Nereocystis luetkeana), Sea cabbage (Sacharina sessilis), and Winged kelp (Alaria marginata) but they also carry one’s commonly used by herbalists such as bladderwrack/rockweed (Fucus vesiculosis)  .   They are extremely nutrient dense as they pull in the ocean nutrients because they are either underwater or bathed in constant waves and ocean spray.

I primarily harvest Sea cabbage and Winged kelp from this category.

Sea cabbage (Sacharina sessilis)  used to be classified as a Laminaria but most of those have been shifted over to the Sacharina genus.  The commonly consumed Japanese “kombu” is Sacharina japonica and our sea cabbage is a close cousin and is an excellent addition to broths, mineral syrups and as a gammassio for flavoring.   You can tell this seaweed because it lacks a “stipe” and sits farther out on the tidal plain, often in large groupings of thick green kelps that hang together on rocky outcroppings.


Winged Kelp (Alaria marginata)  grows commonly along the Oregon Coast and come from a long stipe that attaches to rocks and can measure up to 15 feet long.  These seaweeds have a long midrib that is easily noticeable and fringy, wavy edges.   This is another highly nutritious seaweed and is much thinner and more easy to slice up into strips for soups, or cut up into small pieces for salads.  Sometimes this is called west coast wakame because it has a similar appearance and texture to Japanese wakame (Undaria pinnatifida)



Green  (Chlorophyta)

Green seaweeds are abundant in chlorophyl and are commonly found in fresh water but also marine aquatic habitats.  The only main seaweed I gather from this grouping is Sea Lettuce (Ulva fenestrata).  This is a bright green seaweed that drapes itself over rocky outcroppings and is somewhat delicate, a tad rubbery and nori like.

Sea Lettuce  (Ulva fenestrata)



Red  (Rhodophyta)

Red seaweeds contain about 60000 species and the chlorophyl is masked by other phycobilin pigments.  I gather 3 of these types of seaweeds regularly.  Lets take a look.


Nori/Laver  (Pyropia sp.)  Most all of us know nori from Japanese cooking.  Found easily on rock outcroppings often a little higher up on the beach, this genus (Pyropia) is found throughout the world and has been used commonly in traditional cooking in places it grows.  Nori is slightly rubbery and is less iodine rich than the kelps.



Turkish Washcloth  (Mastocarpus papillatus)  Sometimes it is challenging to differentiate some of the red looking small seaweeds but both Turkish washcloth and Turkish Towel have small scaly rough papilla that is easily visible.  Turkish washcloth makes for a great seaweed snack or as part of a larger combination of seaweed gamassio.       


Dulse  (Palmaria palmata)  is one of the more friendly red seaweeds and looks somewhat like Turkish washcloth but lacks those telltale papilla while retaining bisected  fronds coming from a singular stipe.






So while you don’t need to be an expert, it is key that you understand some of the basics of harvesting seaweeds.  There first is to really understand when the harvesting rules are in your state.  That means knowing what beaches allow harvesting and what don’t as well as the timing and allotment you are allowed.  When harvesting its key to wear a pair of slip proof shoes to avoid nasty falls.    Its also key to know your tide tables and to harvest mainly at low tide.  Never gather seaweeds that have been ripped loose and are lying on the beach.

Instead gather by snipping about half of the seaweed with scissors but never pulling them from their holdfast so that they cannot grow again. Think of them as long blades of grass that will grow back- but make sure you don’t gather more than about 10 percent from one area to insure the health of their ecosystem. Also, its key to make sure you are not gathering from anywhere that is polluted industrially. Seaweeds slurp up all the constituents in their vicinity and that includes pollutants as well.

When I gather seaweeds I like to bring a plastic food grade bucket with a handle and some holes that I have drilled myself.  This allows seawater to drip through.  I also bring several mesh bags to put different species of seaweeds in.  After gathering all of the seaweeds, I generally wash them off either in a deep ocean pool or at home in a freshwater tub.  Freshwater will remove some of the saltiness of the seaweed.

As soon as possible I hang the long kelp seaweeds up to dry over a line or hung with clothespins.  The smaller nori, sea lettuce and turkish towel I will simply dry in a mesh rack in a drying room for a few days.  All of them should be dry within a week and then I store in airtight glass containers.





So lets take a look at why seaweeds are so amazing and why they should be part of our regular diet.  Seaweeds by nature are cooling, moistening and nutritious.  That makes them a perfect additive for those who appear hot, flushed, inflamed, overwhelmed with hot, dry conditions in the body such as eczema, swellings, ulcers and hot flashes.  Unless there are thyroid issues, there are strong health benefits to consume a small amount every day.

Nutrition:  The first thing to think about with seaweeds is that they are each unique nutritionally.  The brown seaweeds mentioned above have the most nutrients per gram and also have by far the highest iodine levels.  Anyone with thyroid issues should be very careful integrating iodine rich supplements into their diet and that is especially the case with kelp/kombu and wake. All seaweeds are high in calcium, iron,potassium, magnesium,  vitamin A, B12, C and K as well as an abundance of trace minerals such as copper, chromium, iodine (more on that later) and selenium. (1)

Improved Digestion:  Seaweeds contain something known as fucoidans, polysaccharides that act as prebiotic for healthy strains of bacteria in the gut.  (2)

Antiviral:  Red and brown seaweeds have been shown to have antiviral properties (3) for helping reduce symptoms of viruses such as Hepatitis C.  (3)

Prebiotic:  Seaweeds carry important polysacagrides such as fucoidans that help feed healthy bacteria in the gut.  This is helpful for correcting dysbiosis- a key precursor to symptoms such as “autoimmune and allergic diseases, obesity, inflammatory bowel disease (IBD), and diabetes.” (4) (5)

Cancer:  Numerous studies have shown good results for seaweeds in reducing cancerous malignancies such as colorectal and breast cancer. (6) (7) (8)

Cardiovascular: Polyphenols originating from seaweeds have been shown to be helpful in reducing cardiovascular disorders such as high blood pressure and metabolic syndrome.  (9)

Removes Toxins:  Seaweeds contain phycocolloids that can trap  metallic waste as well as radioactive particles in the body that can then be eliminated.  This is the main reason we should be careful of where we harvest seaweeds. They can absorb the same toxins from the sea that they can trap, absorb and eliminate in the human body. This makes it useful for folks who have experienced heavy metal poisoning but also helpful for people undergoing radiation therapy for cancer.  (10)

Iodine:  One of the key issues with seaweeds has to do with levels of iodine.  For those with thyroid disorders, iodine can interfere with the process of regulating inoportant thyroid hormones.  While those with no thyroid issues can benefit from some iodine intake from seaweeds, those with thyroid issues such as hashimotos and hypothyroidism should strongly limit their consumption, especially of the very iodine dense outer brown seaweeds such as kelp, bladderwrack (Fucus sp) and Wakame.  Nori and dulse have far less iodine per gram than those seaweeds.  (11)

Contraindications:  Those with thyroid imbalances should be cautious in excessive use, especially of the iodine rich seaweeds such as kelp.  IN general all people should be cautious of over consuming seaweeds as they have been linked with higher rates of thyroid cancers.

Dosage:  So knowing this how much should an individual consume regularly?  I would recommend no more than a gram of brown seaweeds or a gram and a half of a mix of green, red and brown seaweeds every day.  This comes out to about a half teaspoon of raw seaweed, added as a garnish or taken in capsules. The main reason for keeping amounts of brown seaweeds down is that they can carry too much iodine for regular consumption.

I will give a caveat to this though.  Iodine levels are reduced strongly by placing seaweeds in hot water.  Traditionally in Japan most seaweed is placed into broth or miso soup where much of the iodine can evaporate out.    So larger amounts of seaweed can be consumed in this way- up to 3 grams in soups/broths.

It can take some time for the digestive tract to get used to seaweed fiber and polysaccharides and some can get stomach disturbances as the body adjusts.   Here are some examples of dried seaweeds from the Oregon Coast:


Kelp (Sacharina sessilis) Wakame (Alaria marginata) and Dulse (Palmaria palmata) from top to bottom


1 gram of Kelp flakes- about a half teaspoon.


1 strip of kelp- 1.5 grams




Seaweeds go well in a variety of dishes such as soups, broths, salads and as a spice to add to meals for flavoring and nutritional value.

As I mentioned above in dosage- you want to consume far less seaweed raw than if you add it to hot water where some of the iodine can evaporate off.  This is especially true of the high iodine content kelp (Sacharina sp) and wakame (Alaria marginata).


Seaweed Jerky:  Below is an example of some wakame  (Alaria marginata) jerky.  Take the seaweed and cut off one gram strips and simply suck and chew on it as if it were jerky. It is highly mineral and vitamin rich and just a tasty chew.  You can try this with the kelp (Sacharina) as well but I prefer the wakame.


Seaweed Garnish:  One can simply take a few seaweeds and place them in a coffee grinder and powder the seaweed until flaky.  Then add a quarter teaspoon at a time to meals.


Bone Broth with Kelps (Sacharina and Alaria):   One of the best ways to work with seaweed is by adding it to your bone broth.  I take the chicken bones from a roasted chicken and place it in a pot with water to cover and 2 tablespoons of apple cider vinegar.  Then I add a mix of nutritive, aromatic and adaptogenic herbs as well as two to four sticks of kelp and a handful of dulse.  Then allow to simmer for up to 24 hours and then strain.


Dulse/Nori  snacks: Place dulse and nori in a bowl and mix in with a tablespoon of olive oil.  Then place in oven at 300 for about 5 minutes and then remove and eat as a snack.


Seaweed Miso Soup:   Simply add water to a pot and heat up to hot (not boiling).  Add miso paste to taste and stir in until dissolved.  Add sliced tofu, scallions and cut pieces of wakame or nori.  Allow to sit for a few minutes until the seaweed has reconstituted.  Enjoy!





Seaweed has long been a staple of traditional coastal societies throughout the world.  Though Asian consumers have had an unbroken tradition of consuming seaweeds regularly, those in the US have only just started to turn on to the amazing healing powers of seaweeds.  With the advent of seaweed snacks becoming popular, more folks are interested in consuming and foraging for seaweeds.  Seaweeds are not only immensely nutritious, they have tremendous healing powers for numerous conditions.  This article has been a brief foray into the wonders of seaweed harvesting.   I would however suggest that folks interested in this practice take a class with a good seaweed teacher to help you with identification and ethical gathering.




This article written by Jon Keyes, Licensed Professional Counselor and  herbalist.  For more articles like this, please go to  You can also find me at the Facebook group Herbs for Mental Health.






1- Minerals from Macroalgae Origin: Health Benefits and Risks for Consumers  Ciruncisao, Catarino, Cordoso and Silva

2- Nutritional and digestive health benefits of seaweed.  Rajapakse and Kim

3-Antiviral Profile of Brown and Red Seaweed Polysaccharides Against Hepatitis C Virus   Gheda, El-Adawi and El-Deeb

4-Emergent Sources of Prebiotics: Seaweeds and Microalgae  Raposo, Bernardo de Morais and Costa de Morais

5- Effects of the Brown Seaweed Laminaria japonica Supplementation on Serum Concentrations of IgG, Triglycerides, and Cholesterol, and Intestinal Microbiota Composition in Rats Kim, Kwon, Kim et al

6- The consumption of seaweed as a protective factor in the etiology of breast cancer: proof of principle  Teas, Vena, Cone and Irhimeh

7-Seaweed and Cancer Prevention Tokudome, Kuriki and Moore

8- Fucoidan and Cancer: A Multifunctional Molecule with Anti-Tumor Potential Atashrazm, Lowenthal, Woods, et al

9- Potential Role of Seaweed Polyphenols in Cardiovascular-Associated Disorders  Gomez-Guzman, Nogales, Algieri et al

10- Sea Vegetables for Food and Medicine  Ryan Drum

11- Medicinal Uses of Seaweeds   Ryan Drum

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