St. Lawrence species

Sieve kelp

Agarum clathratum

Type of resource

  • Algae
  • Brown algae

Other names

Sea colander

Status of the resource

  • Not a cause for concern

In season

Fresh in late spring (rarely sold in this form).

Processed all year round. Generally as a dried product.

SIZE : Up to 2 m long and 50 cm wide.

LIFE EXPECTANCY : From 5 to 6 years.


To reproduce, sea colander kelp releases spores that generate organisms called gametophytes. They in turn produce male and female reproductive cells. When they meet, a new sea colander is formed.

Sea colander kelp is a large, dark-brown seaweed characterized by a frond that’s riddled with holes. It has a broad midrib and a short, smooth, cylindrical stipe.

It adheres to the substrate by means of a holdfast.

Coastal zone, between 10 m and 40 m deep, or even more when the water is clear enough to support its development. It is therefore the last algae you will encounter.


Sea colander attaches itself to rocks, between sugar kelp and Atlantic wakame, when enough space is available.
Credit : Richard Larocque, photo taken in Les Méchins.


Solar energy



Herbivorous mol-luscs
Grazing fish

A strange colander

The numerous holes in its frond improve nutrient exchanges by increasing water turbulence against the leaf surface. These holes are, in fact, what have earned it the name Sea Colander.

MACHINES : Hand harvesting.

Permit required. Cut the colander with a sharp object, without tearing off the base.

Sea colander is said to have antioxidant potential.

Sea colander is mainly used to prepare broths. Dried and flaked, it is used as a seasoning, for example in veggie pâté.

It has a rather sharp taste and acts as a natural flavor enhancer.

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.