St. Lawrence species


Ulva intestinalis

Type of resource

  • Algae
  • Green algae

Other names

Aonori, aosa

Culinary name


Status of the resource

  • Not determined

In season

Fresh in summer.

Processed all year round. Generally as a dried product.

SIZE : Between 10 cm and 30 cm.

LIFE EXPECTANCY : Less than one year.

LIFE CYCLE : Ulvae reproduce by releasing male or female cells, which then fuse to form a new alga.

Once the reproductive cells have been released, certain parts of the algae turn white and die. Not to worry, the algae will later regenerate from spores.

This algae grows mainly in summer, especially in nitrogen-rich environments.

Gutweed is a tube-shaped algae with no branching. These tubes are long, thin, and filled with air. It has a small disk-shaped holdfast from which the tubes grow.

The color is a somewhat translucent, bright green.

Coastal zone, up to 10 m deep.

Gutweed tolerates variable salinity and can be found in a wide variety of environments: ditches, rocky basins, estuaries, lagoons, marine water, etc. However, it favors calm environments.

There are 16 different types of gutweed in the St. Lawrence. Gutweed is the most widespread. It is found worldwide.
Credit : Éric Tamigneaux, photo taken in Pointe-Saint-Pierre.


Solar energy


Herbivorous molluscs
Grazing fish

MACHINES : Hand harvesting.

Harvesting requires a permit. Use a sharp object to cut the algae above the holdfast, so as not to tear it off.

Gutweed is rich in protein, iron and calcium, as well as vitamins B and A. It contains high levels of nitrogen and phosphorus, making it particularly effective as a natural fertilizer in agriculture.

Tastes similar to spinach, with a hint of iodine.


  • Add raw to salads.
  • Use its dried, flaked version to enhance the taste of dishes.

The waters of the St. Lawrence are known for their good quality. However, as algae absorb the elements present in the water in order to grow, it is preferable to make sure that the harvesting site is clean before eating them fresh.