|Kelp is the forest of the ocean. Like the forest, it has its seasons. In winter storm waves rip pieces or entire kelp plants from its tenuous grip on the bottom. The pieces float about, often washing up on beaches. In spring, the open spaces are filled by new plants. Fronds grow quickly, up to 18 inches per day. The thick frond canopy darkens the water underneath, providing residents with hiding places from passing predators. The fronds cut the sunlight reaching the bottom, preventing certain algae from growing and allowing other types of plants to colonize the bottom. The kelp provides living space, protection and food for many creatures that depend on it for their existence. From is spreading fronds floating on the surface, to the leaves distributed in the water column, to the holdfasts that anchor the strands to the bottom, kelp provides a place for life to flourish.
Many types of kelp are edible for humans. Japanese are particularly fond of the stuff. Sushi is wrapped in it. It is filled with many vitamins and is often incorporated in macro biotic diets and food supplements.
Kelp is a member of the large group of mostly aquatic plants called algae. As unlike their microscopic brethren as you could imagine, kelp can grow to heights of 100 to 150 feet. While we are frequently and unfortunately acquainted with algal blooms in the Chesapeake Bay, west coast algae takes the more larger forms of seaweed and kelp.
There are three major types of algae.
Green Algae are colored green and have a chemistry most like land plants. Sea lettuce is a common green algae that is found on both the east and west coasts.
Red Algae have thousands of species, many found in and on the tidal rock pools of cool water. Red seaweeds range from pink to red to purple.
Graphics from Monterey Bay Aquarium
Brown Algae are brown or golden green. They are found in rock pools too, but as much smaller plants able to hold up to the battering in the intertidal zone. The most prominent members of the kelp family are the large kelps waving back and forth in the deep water of the surf zone.
Kelp share a basic form of holdfast, stipe and blade the kelp equivalent of roots, trunk and leaves. Bull kelp grows a long single stipe the diameter of a thumb from its holdfast. That stipe slowly increases in diameter with an increasing large hole in the center that acts as a float. At the very top is a spherical end where the blades sprout out, each long blade emanating directly from the top of the stipe.
The bull kelp beds begin at a depth safe from the lowest low tides and surf and grow to a water depth of 100 feet They require strong currents or wave action to grow successfully. The are built to survive and thrive in the constant turbulence of the surf zone. There they float with the blades streaming in the wash. At low tide the float part of the stipes lie against each other and came prove difficult to paddle through. Inside the kelp line, both the surf and the current can be considerably reduced. the blades of the kelp are curled and twisted which keeps them turning in the current. This keeps the blades from being dried out in the sun as they float at the surface.
Bull kelp floats along the shore
Giant kelp sends several stipes up from its holdfast, with blades appearing along the entire length of each stipe. Each blade has its own float. Not as hardy as the massive bull kelp, it prefers quieter waters where the wave action is reduced but there is still good water flow.
Giant Kelp Photo courtesy NOAA
Feather boa kelp begins as a stipe with a single blade at the end of the stipe, but later more primary and secondary (smaller blades) grow along the stipe. Floats are distributed along the stipe. Stipes grow to 50 feet.
All the kelps near an environment where they can get a good grip on the bottom and where cold nutrient rich waters flow over their blades, bring nourishment and carrying away waste.
Kelp absorbs its nutrients directly from sea water. Its "roots" play no role in the nourishment of the plant. It simply provides an anchor to keep the kelp in one place. In the spring and summer, when nutrients and sunlight are plentiful, kelp grows quickly to form a dense canopy that block sunlight from the rest of the water column. Individual kelp live for as long as 10 years. Old kelp fronds and plants torn from the hold on the bottom do not drop to the kelp forest floor, but float away, most to deeper water but some to be washed up on the beach.
Kelp is grazed by a number of different creatures, but the most prolific and destructive of these are sea urchins. They can make survival difficult for even the fast growing giant kelp. Fortunately for the kelp, they have defenders. Sea otters eat urchins. Where there are sea otters present, sea urchins are forced to hide in crevices where the otters can't get them. Currents bring drifting pieces of seaweed to them. The sea otters patrol the kelp and keep the urchin numbers down allowing a healthy balanced kelp forest to develop.
Graphics from Monterey Bay Aquarium
Kelp Interactive from Monterey Bay Aquarium