E-Flora BC: Electronic Atlas of the Flora of British Columbia

Family Description:
Members of this family have a single, terminal blade that is divided in some species. The stipe is rarely branched. Blades are smooth or undulate, entire or with holes, of uniform thickness or with a central, thickened region (midrib). Sori develop directly on the blades.

Species description:
This brown alga grows on rocks. The stipe is up to 30 cm (about 12 in) long (but is almost always much shorter) and arises from a highly branched holdfast composed of rather narrow haptera. This stipe supports a single undivided blade that is rather stiff and riddled with numerous small, natural holes responsible for most of the common names of this species. The blade grows to 90 cm (about 35 in) long and 50 cm (about 20 in) wide and has an indistinct, broad midrib. The blade is somewhat heart shaped where it joins the stipe.

Sieve Kelp belongs to a very distinctive genus not easily confused with any other algae. Although the tide rarely goes low enough for you to see it in its natural habitat, it sometimes gets torn off and thrown onto the beach by storms.

In Washington State, Sieve Kelp is avoided by urchins and so can form large stands. In Southeast Alaska and westward, dense forests of Sieve Kelp can occur just below extreme low water mark on rocky shores that have been otherwise heavily grazed by the Green Sea Urchin (Strongylocentrotus droebachiensis). Once established, populations of Sieve Kelp persist for many years because it is perennial. Certainly it is unappetizing as human food, especially when there are so many other far more edible species abundantly available. Sieve Kelp is low in caloric value (2.86 Calories per gram of dry weight).

Beds of Sieve Kelp are, however, important nurseries for juvenile Spot Prawns (Pandalus platyceros), which spend their first year (southern British Columbia) or two (Southeast Alaska) there after settling out of the plankton.

At Auke Bay, Alaska, researchers have shown that this species can produce spores in its fifth year of life and can survive into its sixth year.