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.
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.
Some of the adaptations that make it easier for kelp to survive here are:
A holdfast that secures the plant to the bottom.
A flexible blade that conforms to the shape of the wave, thereby reducing wave drag.
A microscopic gametophyte generation (not illustrated) separate from the large sporophyte generation. Why would this be an advantage?
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.