Division Phaeophyta, Brown Algae

Brown algae are all multi-cellular, and are found in a variety of different physical forms including crusts, filaments, and large elaborate kelps. Like all photosynthetic organisms, brown algae contain the green pigment chlorophyll. They also contain other gold and brown pigments, which mask the green colour of chlorophyll. The dominant pigment found in brown algae is called fucoxanthin, and it reflects yellow light. Because of their combination of pigments, the colouration of brown algae ranges from light olive green or golden, to very dark brown. Most brown algae live in the intertidal or shallow subtidal zone, and they are most abundant in the colder oceanic waters of the Northern Hemisphere.

Humans use brown seaweeds in numerous ways, and algae are becoming very important commercially for food, cosmetics, pharmaceuticals and in the sciences. Many tasty kelps are harvested from wild populations and also grown in commercial kelp farms. Two unique types of compounds are found in brown algae, algin and fucans, which are used in the manufacturing of consumer goods. Algin is found within the cell walls of brown algae, and it is an emulsifier used in food products. Fucans are the slimy stuff found on kelps, and have potential medicinal uses. Brown algae are also collected, treated, and sold as a fertilizer for terrestrial agriculture.

Egregia menziesii: the "feather boa" kelp

This brown seaweed was named Egregia menziesii after the botanist Archibald Menzies, who first visited the Northwest on a fur-trading vessel, and collected many seaweed specimens from the coastal waters of British Columbia. The common name of Egregia menziesii is the feather boa kelp, because it looks like a feathery scarf!!

The colour of Egregia menziesii ranges from olive green, to dark brown. This magnificent kelp is found attached to rocks in the low intertidal and subtidal zones along moderately exposed coasts from Alaska to Mexico. It is one of the largest intertidal kelps, and can reach 20 metres in length. It often grows in dense patches in the shallow subtidal zone, forming a lush canopy. Egregia attaches itself to the rocks with a strong holdfast made up of many haptera. It has a long stipe that is cylindrical at the base, and branches irregularly. The upper part of the strong stipe is flattened and strap-like. The stipe is densely covered with numerous elliptical floats and small, broad blades, which are up to 5 centimetres long, and 1 to 2 cm wide. Limpets are often observed on the stipe of Egregia.

Like other large brown kelps, Egregia menziesii has been used as a fertilizer by coastal farmers.

Alaria - the "winged" kelp


The word Alaria means wing in Latin, and the common name for this group of seaweeds is the winged kelps. There are 14 species of wonderful winged kelps found in the Arctic, North Atlantic, and North Pacific oceans. Winged kelps are popular food items, and are eaten by people around the world.

Alaria marginata is one species of winged kelp that is commonly found in the Pacific Northwest. It can be seen clinging to rocks in open and protected waters from Alaska to Mexico. This grand species can grow up to 3 metres in length, and is abundant in the low intertidal and shallow subtidal zones. The colour of Alaria marginata ranges from olive green to deep brown.

The hearty holdfast of Alaria marginata is made up of many slim, branching haptera. The short stipe is usually less than 30 centimetres in length, and has a cylindrical shape near the holdfast. Where the large vegetative blade starts the stipe flattens out to become a midrib. The grand vegetative blade has a distinctive midrib and can grow up to 2 metres long and 20 centimetres wide. The characteristic golden midrib is generally about one centimetre wide and runs along the entire length of the vegetative blade. If the end of the blade gets worn and shredded the midrib may extend beyond the end of the blade. At the base of the majestic vegetative blade mature Alaria plants have 2 rows of smaller, reproductive, spore producing blades called sporophylls. The sporophylls grow on opposite side of the stipe and are 10-20 centimetres long and 2-3 centimetres wide. The size and shape of the petite sporophylls is a characteristic used to distinguish between the different species of Alaria.

Hedophyllum sessile - the stipe-less kelp

Hedophyllum sessile is also known as the stipe-less kelp, and as sea cabbage. This brilliant brown seaweed grows in the mid and low intertidal zones of the Pacific coast from Alaska to California. It is found in both wave exposed and sheltered sites, and is often seen washed up on the beach after rough storms.

The sturdy holdfast of Hedophyllum sessile is highly branched, and because it is a stipe-less kelp the blades originate from the holdfast. The blades form a lush canopy which often cover the many haptera that make up the holdfast. The luscious blades are light to very dark brown in colour, and are generally between 30 centimetres and 1 metre in length. The blades of Hedophyllum sessile take on different appearances depending on the amount of wave action and water motion in their environment. Where wave action is greatest the blades have a smooth texture, and are split into slender, strap shaped segments 5-10 centimetres wide. In sheltered environments the blades are usually larger, have a ruffled, wavy form, and few longitudinal splits. The unruffled, split blades are thought to offer less resistance to water motion, allowing these plants to remain attached to the rocks in wave exposed environments.

Hedophyllum sessile is another tasty kelp that adds flavour, colour, and texture to soups, casseroles and many other dishes.

Lessoniopsis littoralis - the strap kelp

Lessoniopsis littoralis is a wonderful, woody kelp and is also known as the strap kelp. It is a sturdy seaweed that is found only in the low intertidal zone in wave exposed environments along the rugged Pacific coast from Alaska to California. It is usually dark brown in colour, and may grow up to 2 metres in length. Lessoniopsis littoralis is a perennial species, which means that the plants live for more than one year, although they may lose most of their blades during violent winter storms.

The holdfast of Lessoniopsis littoralis is stout and woody, and looks like a miniature tree trunk. The holdfast and stipe base can be up to 20 centimetres thick, and 40 centimetres long. The stipe system is also woody and branches repeatedly. At the end of each branch is a long, flattened blade with a midrib. The slim blades are 7-12 millimetres wide, and up to 1 metre long. The midribs are usually located in the centre of the blade, and are 2-3 millimetres wide. Very old, mature Lessoniopsis littoralis plants have many, many branches, and may have up to 500 blades. Sporophylls, which are spore-producing blades, are sometimes found on mature plants. The sporophylls are smaller than the vegetative blades, and are found at the base of older vegetative blades.

Nereocystis leutkeana - bull kelp

Nereocystis leutkeana is an amazing species of brown seaweed that also goes by the name bull whip kelp, or simply bull kelp. Bull kelp is found along protected and open coastlines of the Pacific from Alaska to California. It grows in the subtidal zone in up to 20 metres of water.

Nereocystis leutkeana is one of the largest brown seaweeds, and can grow to lengths of 40 metres!!! The seaweed body consists of a large branching holdfast with many haptera, a very long tubular stipe, a single bulb-shaped float, and numerous long, smooth, broad blades. The stipe can grow up to 36 metres long and ends at the water's surface, where the float is attached. The float generally has a diameter of 10 to 15 centimetres, and is filled with up to 3 litres of buoyancy gases. One of the gases found in the float of bull kelp is carbon monoxide, a wicked poison. Attached to the float are 2 clusters of golden brown coloured, strap shaped blades, which grow up to 4 metres long and 20 centimetres wide, and float on the water's surface. Bull kelp grows in large kelp forests, and the blades create lush surface canopies. Kelp forests provide shelter for many marine fishes and invertebrates, and are an important food source for sea urchins.

Nereocystis leutkeana is an annual seaweed, which means that each plant grows for only one season, and then dies off. The plants die and become dislodged in the winter, and are washed ashore during powerful storms. The growing season of bull kelp is quite short, generally only from March to September, so they must grow very quickly!! In order to reach a stipe length of 36 metres (maximum) a plant would have to grow 17 centimetres a day!!

In the late summer and early fall you can often see dark brown coloured patches on the blades of bull kelp. These dark areas are spore patches, which hold groups of spores, and are called sori. The patches fall out from the rest of the blade and settle onto the bottom. Once the spore patch reaches the substrate the spores are released and they grow into tiny, microscopic male and female gametophyte (gamete producing) plants, which reproduce sexually. The male gametophyte plant then releases sperm, which is attracted to the egg, which is retained by the female gametophyte. After the egg is fertilized the zygote (fertilized egg) grows into a new sporophyte. The sporophyte (spore producing plant) is the large seaweed described above.

Bull kelp is a common seaweed, and several uses for this abundant kelp have been discovered by humans. Along with other brown algae, bull kelp has been collected, treated, and sold as a fertilizer for terrestrial agriculture. Nereocystis leutkeana is also a popular and tasty food item for humans, and it is harvested commercially for fresh and dried food products.

see more about intertidal Phaeophyta!

References

Druehl, L. 2000. Pacific Seaweeds. Harbour Publishing, Madeira Park, B.C., Canada.

Harbo, R.M. 1999. Whelks to Whales Coastal Marine Life of the Pacific Northwest. Harbour Publishing, Madeira Park, B.C., Canada.

Waaland, J.R. 1977. Commom Seaweeds of the Pacific Coast. J.J. Douglas Ltd., Vancouver, B.C., Canada.

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