Oysters and seaweeds

Oysters and seaweeds

Oysters have a symbiotic relationship with seaweeds. Some shellfish industries utilize this knowledge by cultivating the two in the same ecosystem. Furthermore, the market for shellfish grows every year with consumers wanting clean, high quality oysters that are sustainably grown; therefore, it is worth looking at the relationship of oysters and seaweeds.

Oysters and seaweeds symbiosis

oysters and seaweeds, rockweed
Collecting oysters from the rock pools where rockweed, fucus distichus, seaweed grows
oysters and seaweed symbiosis
Fanny Bay oysters growing beside sea lettuce, Gabriola Island

Firstly, seaweeds remove and utilize the nitrogen and phosphorus waste products of oysters.  In turn, they provide oxygen for the oysters to grow.  Some cultivated oyster farms have lines of kelp growing beside the oysters. Even in the wild, they grow side by side.  On Vancouver Island, Fanny Bay oysters grow on rocks beside rockweed or on mud bays beside sea lettuce.  When I collect oysters I also collect seawater and the seaweeds to place on top of the oysters for transport home. The oysters will stay fresher that way.

Know the origins of your oysters

Furthermore, grocery store or restaurant served oysters go through a process called depuration: the oysters are placed in clean circulating seawater tanks for 48 to 72 hours to filter out fecal contaminants including harmful bacteria. However, traditional depuration methods may not remove viruses such as Norwalk and Hepatitis A (1). These viruses bind to the gut tissue of the oyster and avoid their filtration systems (1). It is important to know where your oysters come from and that they are not near poor water quality areas subject to sewage.

Oysters and seaweeds share similar aromas

oysters and seaweeds
“Three biter” fanny bay oyster

Flavour depends on three factors  aroma, taste and texture. The aroma from oysters and seaweed arise mostly from dimethyl sulfide (2). It’s that clean ocean smell that can become more fishy or sulfurous in higher concentrations.  Dried rockweed distinctly smells of oysters and is not fishy at all. After all, you are what you eat and the oyster filter feeds the same nutrients and some of the algal elements of the rockweed. Thus, when biting into an oyster, pay attention to the aroma, salt level and texture. For example, some oysters such as Fanny Bay, Kumamoto and Kusshi have a cucumber aroma. Some oysters are saltier depending on the time of year. The texture will change with the season and with how you cook the oyster. I like to roast oysters collected from our clean bay over a campfire to get them to open. If I get the oyster off the grill just as it opens, the flesh is slurpy and saltier. If left longer on the flame, the flesh becomes chewier and less briny.

Vegan alternative to oyster mayo

seaweeds and oysters cauliflower burger with wrack mayonnaise

If you like the taste of oysters but are wary of the risk of viral contamination or want a vegan alternative, then rockweed powder is a safe option.  Oyster mayonnaise is often served on burgers, meats and seafood.   I have presented a vegan alternative rockweed mayonnaise served on a very delicious cauliflower “burger”.


The smoky salty flavours of the mayonnaise pairs well with the “meaty” spicy cauliflower and sweet acidic bread and butter pickles.

1 small cauliflower head, leaves and stem trimmed.

1 tsp. ground turmeric

1 tsp. sambal oelek (chili paste)

30ml olive oil

Slice lengthwise down centre of cauliflower stem. Trim florets off each rounded side making 2 “steaks”. Whisk together turmeric, chili and olive oil.  Slather on both sides of cauliflower.  Roast in high oven at 425°F for 10 min. one side, flip, then 15 min. other side until edges caramelize and centre is firm. Roast the trimmed off florets for another meal also.

Rockweed mayonnaise

¼ c vegan mayonnaise

3 tsp. rockweed powder (dry rockweed in 200 F oven for 30min. then grind in spice grinder)

½ tsp. grainy mustard

1 tsp. liquid smoke

Mix together.  Spread on hamburger buns. Add roasted cauliflower, lettuce leaves, and bread and butter pickles. Enjoy with a cold beer.

Vegan Salsa Verde

Vegan salsa verde with roasted potatoes

The salty, acid and herbal flavor of salsa verde will change any bland carbohydrate, eggs, or roasted vegetable into something outstanding. Rockweed replaces anchovies as a vegan alternative.

1 small garlic clove
1 tbsp capers, drained and rinsed
1-2 tbsp. rockweed powder
1 large bunch of parsley
½ bunch fresh mint
1 tbsp red wine vinegar
1 tsp. dijon mustard
250ml olive oil
1 cornichon or gherkin pickle

Chop everything in a food processor. Season to taste.


  1. Mcleod, C. et al., “Final Report: Evaluating the effectiveness of depuration in removing norovirus from oysters”. Seafood Safety Assessment Ltd. and the French Research Institute for Exploitation of the Sea. Feb. 2017.
  2.  Fujimura,T., et al. (25 Feb. 2000). Enzymes and seaweed flavour. Simpson and Haard (Ed). Seafood Enzymes: Utilization and Influence on Postharvest Seafood Quality. New York: CRC Press pp 386. ISBN 978-0-8247-0326-4.