By: Adam Tripi

Brown algae are a member of the phylum Phaeophyta. There are nearly 1,500 different species, most of which are marine species. Brown algae vary in color from dark brown to olive green. The range of color is due to the various pigments, fucoxanthin is the brown pigment and chlorophyl adds the color green. There are many different sizes and forms of brown algae ranging from small filamentous epiphytes to very complex giant kelp, which can reach heights of one hundred meters. To aid in photosynthetic production, the pneumatocysts (gas filled bladders) help keep the brown algae floating on or near the surface of the water. Algae have no roots, stems leaves or flowers. Brown algae can reproduce both sexually and asexually; both the motile zoospores and gametes have two unequal flagella (Britannica Online, 2000).

The life cycle of most large kelp begins when a mature plant releases its spores directly into the water. The release of spores is directly related to the seasonal increase in daylight (Edwards, 1998). These spores settle to a rocky bottom and begin to grow into haploid gametophyte plants, which immediately undergo sexual reproduction. The embryo that is formed remains attached to the female gametophyte and is secured to the bottom by a hold fast (Ricklefs, 1990).

Kelp grows best along coast were the water is well mixed due to a lot of wave exposure. They are not often found in bays. There are some kelp forest on the east coast of North America, but the species lack those found in kelp forest on the west coast of North America. They are found as far south as Cap Cod, Massachusetts and sporadically southward to the eastern tip of Long Island, New York (Kelp Forest, 2000). The cold waters off Alaska and the west coast of North America have large kelp forest with a large variety of species. Along the Southern coast of California large flourishing kelp forest can also be found.

Kelp forests occur in cold, nutrient rich water and are the underwater equivalent of a terrestrial forest. Kelp live a long time compared to other marine plants, once a kelp forest is established it can last up to ten years depending on its locality and exposure to waves (Ricklefs, 1990). The basic form of kelp is a blade, stipe and holdfast. The leave like blade is were the sunlight is absorbed for photosynthesis in order to create that sugars which are carried to the rest of the plant via the stipe. The holdfast anchors the plant to a hard surface. Each family of kelp has its own variation of this simple design.

The family Laminariaceae, which consist of the oarweed are usually simple with a single blade on a short strip. These small compact kelp are well suited for the harsh wave swept rocky environment, where they are most commonly found. Giant kelp and bull kelp are found in the family Lessoniaceae. Kelp of this family have a long single stipe which grows from the holdfast. As the stipe grows to the surface it expands to form a large float from which blades sprout (Monterey Bay Aquarium, 2000). These large and complex kelp form the large forests near shore. The kelp in the Alariaceae family look very similar to the oarweeds but eventually sprout smaller blades along the sides of the main blade. As the weather changes so does the kelp forest.

Like forest on land kelp forest change from season to season and year to year. Sunlight, nutrients, water temperature and storms all effect the growth of the kelp. In the spring when the winds blow the surface water offshore, the cold water rises from the depths. This cold nutrient filled water, along with the extended period of sunlight provides an ideal growing condition for the kelp (Monterey Bay Aquarium, 2000). During this time new fronds of giant kelp sprout from the holdfast, and by June the kelp will create a canopy cutting the light off.

After a long summer of growing the kelp forest becomes filled with life. But in the fall as the wind shifts the warmer water is blown in which hinders the kelp’s growth. The warm water, which has few nutrients along with less sunlight attribute to the stunt in growth. Then as winter storms bring in huge waves that not only break the fronds and shake animals from the blades, but also tear away the kelps holdfast. Once the kelp is ripped away from the rock their holdfast swings around in turn taking out other kelp (Monterey Bay Aquarium, 2000). Dead kelp that have been torn from their holdfast generally get washed up on land or are swept out to sea. Many grazers feed off the kelp in the forest.

Kelp forests have their own food chain that helps them to thrive and flourish. Snails, sea urchins, and other grazers live and feed off the kelp with in the forest. They then fall prey to fishes and sea otters, which are always being hunted by large sharks and sea lions. The crabs and other bottom dwelling scavengers pick up all the scraps that float to the bottom (Monterey Bay Aquarium, 2000). There have been many studies done showing how this unique system can be effected when the web is out of balance. Where otter populations have been rebuilt, the sea urchin populations have decreased and the kelp beds have return to their former abundance (Schindler, 1991).

The predator prey interaction between the otters and sea urchins play a major role in shaping the kelp forest. Sea urchins graze on the kelp which in turn weaken the holdfast. This cause the kelp to be more vulnerable to wave damage which can lead to the death of the kelp. An increase in urchin population will lead to a decrease in the kelp forest (Watt et al., 2000). Sea otters prey on the urchins though. This helps to control the population of urchins so that the forest can thrive. A study done by Schueller (1999) showed the humans can also change the web of the kelp forest by overfishing. The reduction of fish means that there is less food for sea lions and seals. The decrease in these organisms causes the killer whales to prey on the otters. When the otter population decreases the urchin population increases causing the kelp forest to diminish. Even though humans may have a negative impact on a kelp forest, kelp is collected today for industrial purposes.

Various types of brown algae are harvested today for different reasons. Brown algae are a very good source of algin, which is a colloidal gel. The gel is used today in both the baking and ice cream industry because it acts as a stabilizer. Algin is also found in toothpaste, bread, beer and paint. There are several species that are collected and eaten, which is known as a vegetable in the Orient, kombu. Kelp have been harvest because of their great source of iodine and fertilizer (Ricklefs, 1990). Commercial kelp harvesters work from ship that has huge hedge clipper like tools, which can cut off the top four feet and collect the kelp. In California where kelp grows very fast about 100,000 tons is collected a year (Monterey Bay Aquarium, 2000). The change of over harvesting kelp is not likely due to the fact how fast it grows.