Sub-tidal Kelp Zone   3 comments

Sub-tidal Kelp Zone

The Sub-tidal  Kelp Zone is seldom exposed at low tide and therefore does not experience significant fluctuations in temperature and salinity. As the name suggests it is colonized predominately by large brown algae belonging to the genera Alaria and Laminaria.


Laminaria spp. (Kelp) has a long flattened blade attached to a thin, rounded, stipe that attaches to the substratum by means of a branched holdfast. The tip of the blade often wears away due to the action of waves. In general they have a lifespan of about 4 1/2 years.

Laminaria spp.


The macroscopic plant is the sporophyte stage. Sporangia on the edges of the blade produce haploid zoospores. Each zoospore develops into a microscopic, gamete producing a male or female gametophyte. The gametes, formed by cell division in the gametophyte, join in pairs to form a zygote, which grows into the sporophyte plant. Growth in Laminaria occurs between the blade and the stipe. Holes can be punched through the blade above the junction of the blade and stipe with a cork borer. As growth proceeds the hole will move towards the tip of the blade and the new tissue can be measured over time. ____________________________________________________________

Alaria and Agarum are kelps that attach  in the subtidal and in low intertidal tide pools. They have the same general structure and life cycle as Laminaria  described above. Both Alaria ,Agarum, and Laminaria have a branched holdfast, a stipe and a long flattened blade. Alaria also has a mid-rib at the center of the blade. Agarum has holes in the blade . The holdfast secures the alga to the bottom and the long flattened blade conforms to the shape of the incoming wave protecting it from the full force of the wave.


Alaria spp.

Alaria spp.


Agarum spp.


Some of the adaptations that make it easier for kelp to survive here are:

  1. A holdfast  that secures the plant to the bottom.

  2. A flexible blade that conforms to the shape of the wave, thereby reducing wave drag.

  3. A microscopic gametophyte generation (not illustrated) separate from the large sporophyte generation. Why would this be an advantage?

  4. Growth between the blade and the stipe rather than at the blade tip. Why would this be an advantage?



Corallina officinalis is a common red alga in the Red and Sub-Tidal Zones. It is an erect branching alga whose cells are coated with a thick layer of calcium carbonate. It is articulated, giving the alga great flexibility, an adaptation that protects it from heavy wave action. The thick layer of calcium carbonate also helps protect the alga from abrasion. It has a holdfast that attaches to the rock surface.


Porphyra spp , a red alga, commonly found in the Red and Sub-Tidal Zones, consists of a flat thallus, attached to the substratum by means of a short holdfast. Porphyra resembles the green alga Ulva (Sea lettuce). They have a broad, thin, flaccid thallus with ruffled margins arising from a short holdfast. Porphyra is extensively cultivated in Japan and sold under the name nori. It is used in a wide variety of foods and is high in protein, minerals and vitamins.


Dulse (Palmaria palmata), a common  inhabitant of the Red and Sub-Tidal Zones is often found here. The red alga has a basal holdfast  connected to a broad branching blade. Dulse is harvested commercially and in its sun dried form can be eaten raw or used as a flavor enhancer in salads, sandwiches, soups, and stir fries.


The bottom of the sub littoral zone may be covered with closely adhering pink and white coralline algae . Cells of the coralline algae, like those of Corallina, are covered with a relatively thick layer of calcium carbonate, protecting them from heavy wave action and to a certain extent from grazing animals such as sea urchins. They also have a low profile, forming crusts on solid surfaces. This also protects them from heavy wave action.



Several other algae are commonly found in the Subtidal: Chaetomorpha spp. ; Chondrus crispus ; Dumontia spp. ; and Hypnea spp. Many other species of microscopic and macroscopic algae and invertebrates may be found here as well.


 Chaetomorpha spp.


Chondrus crispus


Dumontia spp.


Hypnea spp.


Ulva (Sea Lettuce)  and Monostroma may seasonally colonize large areas within the Brown, Red , and Subtidal zones. The algal body (thallus) consists of a sheet of cells (two cells thick in Ulva and one cell thick in Monostroma). Dried Sea Lettuce is sometimes used as a flavoring agent in soups, salads and other dishes. They are firmly attached to the substratum by basal rhizoidal outgrowths (Holdfast). Ulva has two morphologically similar forms, sporophyte and gametophyte. Cells along the edge of the sporophyte undergo reduction division to produce haploid spores with 4 flagella. Each spore grows into a haploid gametophyte. Cells on the edge of the gametophyte form bi-flagellated gametes through cell division. The gametes fuse and the resulting diploid cell grows into a sporophyte. Both genera produce large numbers of spores and gametes and therefore can quickly colonize open space in the rocky intertidal.




Animals common to this area and the Red Zone are shown at the end of the Road Zone page.

Uses of Select Marine Intertidal Algae

Many of the algae common to our coastline have been harvested commercially. Significant amounts of potash, soda, ash, and iodine have been extracted from Ascophyllum and Fucus from the brown algal zone and the kelps Alaria and Laminaria from the sub-tidal kelp zone. These genera have also been used as manure and animal fodder. Animal fodder made from dried Ascophyllum and Laminaria, in addition to yielding a high percentage of protein, contains quantities of vitamins (B1, B2, B12, C, and E). In addition, marine algae have been used as food for centuries. Some of the ways that they are used are discussed below.

Dried Alaria is available in health food stores. The mid rib is the tastiest part of Alaria. .After the mid rib is excised from freshly collected specimens, cut it into small chunks and eat fresh or use them as flavor enhancers in soups or salads. Dried plants can also be used, however they must be hydrated in freshwater first.

Ascophyllum and Fucus can be steamed or cooked in oil flavored with soy sauce. They also can be used in many other ways. Fucus tea can be prepared as follows: Collect several plants and wash them well in freshwater. Chop them into small pieces and let them air dry. Add several pinches of the dried alga to a cup of boiling water and steep for several minutes. Add more Fucus as needed. The dried alga should be stored in an air tight contained or plastic bag. Fucus receptacles can be eaten raw. The receptacles taste a bit like olives.

The blade of dried Laminaria (Available in health food stores) is commonly used as a flavoring in soup. After hydration it can be eaten as is, coated with sugar and consumed or used as a flavoring in wok prepared dishes. Larger pieces of the blade can be fried in olive oil and eaten like a potato chip. Fresh stipes cut horizontally into thin round chunks can be eaten raw or flavored in sweet or sour pickle juice (throw out the pickles and use the juice).

Palmaria (Available in health food stores under the name Dulse) is common in the red and subtidal kelp zones. Collect several fresh plants, wash thoroughly, and air or sun dry making sure that they remain pliable, but not moist. Store in a sealed baggie. They can be eaten raw or added as a flavoring in soups, salads, or other dishes. The taste reminds me of the smell of the sea on a good day.

Porphyra (available in health food stores as Laver) is often used to wrap rice, vegetables such as avocado, and/or raw fish. This red alga is common throughout the intertidal. Collect several fresh plants and wash thoroughly. Air or sun dry. They should be pliable. Store in a sealed plastic baggie. Laver can be eaten raw or added as a flavoring to soups, salads, or other dishes.

Ulva or sea lettuce is easily accessible in tide pools at mid and low levels. There are many ways the sea lettuce can be used in cooking but my favorite is sea lettuce soup. Collect fresh plants and wash well in cold fresh water. Air or sun dry the plants. Break the sea lettuce into small pieces. Bring one quart of chicken broth and one quart of water to a boil and add vegetables such as carrots, broccoli, and celery. Onions also work well. Add the desired amount of diced chicken. Cook until the vegetables are done and then add the cup of sea lettuce. Cook for about 10 minutes and serve. Sea lettuce can also be used in place of grape or cabbage leaves to wrap various types of food.



Posted December 15, 2011 by zottoli

3 responses to “Sub-tidal Kelp Zone

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  1. Wonderful, helpful photos and website, thank you!

  2. I see that the post is quite old, but still comment to say that I liked. Thank you very much.

  3. Have good content on the blog, I congratulate you. I will keep coming occasionally to view updates, since I see that the post is old. kisses

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