The brown algae are the algae, which a lay often comes across and relatively fast knows what type of algae they are. At the seacoasts, they determine the image of the alga vegetation and show themselves in great quantities at low tide and after storms. Their highly developed, often variously arranged vegetation bodies rarely measure more than 50cm; some of them reach a length of 10m, and those who live in the colder seas can even reach a length of 100m. From the 250 kinds with approximately 1500 types, a large majority lives in the oceans, particularly in the moderate and cold parts. They occur in large stocks and play a big economic role in Eastern Asia as raw material suppliers and as food. The systematically well outlined group of brown algae is very old: Fossil forms are well-known since Devonian. They’re relative families are the gold and flint algae. The easily built cell wall of the brown algae mainly consists of cellulose and their metal salts.
Ecology and Meaning
The brown algae are in their majority, inhabitants of the tidal zones at the coasts of the oceans. In fresh water only Heribaudiell, Lithoderma, Pleurocladia and Bodanella as well as some types of Ectocarpus and Sphacerlaria fluviatilis can survive. Thereby, they obviously group themselves under the influence of tides, the condition of the underground as well as the intensity and composition of the light into so called belts, whose floristic composition changes with increasing depth. Impressive is the picture, which the giant seaweed forests offer at the California Pacific coasts. To a depth of 25m the alga vegetation consists of clear from each other issued and characteristically assembled societies. The enormous production - it is estimated to be 10-15 t/ha algae per year is of considerable economic importance. The algae are harvested regularly for the production of the Alginate. The use of brown algae as food is very old. However, it plays a small role in the daily live in Western Europe: only the young, fresh stacks of Laminaria saccharina and Alaria esculenta are eaten. However in Eastern Asia, Kombu is an important food. Laminaria japonica, Alaria crassifolia are used as green Kombu, eaten like any other vegetables or used pulverised as soup or spice. Tea can also be prepared. The dried up stocks can be easily harvested at low tide. They serve as fertilisers or, converted to alga flour in factories, can be used as vitamin and in addition to animal food.
The multiform, usually multi-cell and often quite complicated built red algae with approximately 675 kinds and about 4100 types take, because of different reasons, a privileged position within the alga family. Their predominantly reddish, rare violet or cyan coloured vegetation body usually live on the coastal area of the seas; only few forms live in the fresh water. Together with the brown algae they dominate the alga family at the seacoasts, however penetrating into deeper depths (up to 180m). The differently colouring of the body is based on the different quantitative proportions of the red and blue pigments. As assimilation product, florid starch is stored in form of pellets which are situated in the zytoplasm. The red algae are one of the oldest groups, which independently developed and don’t have direct relations with other algae families.
Occurrence and Spreading
The large majority of red algae live in the sea. Only about 50 well-known types live in fresh water, where mostly pure running waters are settled. The marine forms seem to occur particularly frequently in the Australian area and in warmer seas. The fact that the temperature for its geographical spreading is of decisive importance must be the results from the fact that some types do not even bear a yearly fluctuation of 5 degrees Celsius. A prerequisite for it, to achieve depths around 180m is transparent, fresh water. In the cloudy Atlantic they only exceptionally live in 30m depth and even in the transparent water in front of Florida they only achieve a depth around 70-80m.
The economic meaning
Many red algae are important food although they are only regularly used as human nutrition in Eastern Asia. The utilisation of Porphyry types play a large role in the so-called Nori- industry. In the autumn Japanese Fischer sink bamboo or oak bundles as well as coconut or hemp fibbers into the shallow sea, where spores and sprouts settle. Later the bundles with the young plants or wets are brought into water with less salt, where Porphyry develops optimally. At low tide fisher harvest from boats. The washed algae are cut and spread on bamboo mats to be air-dried.
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In some areas of the Indian ocean the sea surface lights up at night. It is so bright that one can read a newspaper. This light is caused by tiny sea algae, the Dino-flagellata. Sometimes the lightened surface has a diameter of more than 1.5 km.
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