St. Lawrence species

Sea lettuce

Ulva lactuca

Type of resource

  • Algae
  • Green algae

Other names

Aonori, aosa

Status of the resource

  • Not determined

In season

Fresh in summer.

Processed year-round, generally as a dried product.

SIZE : From 15 cm to 30 cm, up to 50 cm.

LIFE EXPECTANCY : Less than a year.

LIFE CYCLE : The ulvae reproduce by releasing male or female cells that fuse to form a new alga.
Sea lettuces are small in the spring. They develop mostly during the summer when the water is warm. Growth takes place at the extremities, either the holdfast or the fronds. In fact, they don’t even need to be attached to the substrate to grow.


Sea lettuce has no stipe. Its frond is extremely thin and flexible, translucent green in color, but can sometimes be darker. It has a wavy edge and a small holdfast.

Coastal zone, up to 10 m in depth, in salt or brackish waters.

Sea lettuce prefers calm, moderately exposed environments, because it detaches easily.

It is a rather dispersed alga. You will not find it grouped together in dense underwater forests.

Credit : Éric Tamigneaux



Solar energy


Herbivorous molluscs


MACHINES : Hand harvesting.


Harvesting requires a permit.

May to December in the Gaspé Bay and May to June in Haute-Gaspésie.

Only every second frond can be harvested at low tide in the inter-tidal zone.

Credit : Éric Tamigneaux

BENEFITS : Sea lettuce is rich in protein, vitamin B12, iron, calcium, and magnesium. It also contains starch and a good quantity of fiber.

It can also be used as a natural fertilizer, thanks to its high nitrogen and phosphorus content.

LET’S COOKFresh, full-bodied taste. Its flavor is similar to that of spinach, with an added hint of the sea. Its texture is tough when raw, but softer when cooked.


  • Freshly picked, sea lettuce can be consumed directly, thinly sliced; for example in salads, sauces or in soups.

The waters of the St. Lawrence River are known for their good quality. However, like other algae, sea lettuce absorbs elements from the water in order to grow. It is best to ensure that the harvesting site is clean before eating it fresh.

Mirror, mirror

Sea lettuce is so named for its culinary qualities and its shape, which are very similar to that of lettuce leaves.