Algae

Algae are the most important primary producers on Earth. The total amount of organic carbon produced through their photosynthesis is approximately seven times that of higher plants. At the same time, the nitrogen-fixing algae (and nitrogen-fixing bacteria) can fix about 170,000,000 tonnes of nitrogen every year. Algae are not, therefore, only an important source of food for mankind and animals, they are also the most important source of atmospheric oxygen given out from their photosynthesis. The algae exert a profound influence on the material cycles of natural ecosystems as well as environmental quality.

The algae are distributed widely in oceans and various inland waters (including lakes, reservoirs, rivers, streams, marshes, ponds, springs, ice and snow) as well as wetland surfaces. Among them, those which live in inland freshwater bodies are freshwater algae, while those distributed in the sea, oceans and inland saltwater bodies are saltwater algae. China's algae include representatives of the Cyanophyta (Procaryotes), Bacillariophyta, Pyrrophyta, Chrysophyta, Xanthophyta, Cryptophyta and Euglenophyta (Protista) and Rhodophyta, Phaeophyta, Chlorophyta and Charopbyta (Plantae). Two thousand, four hundred and fifty eight species of marine algae have been recorded from China (See also Section 3.9, Biodiversity in China's Seas, Coasts and Islands). Here, only the biodiversity of China's freshwater algae and the threats to it are discussed.

(1) Diversity of freshwater algae in china

Owing to the large territory and the varied natural environment of China, the freshwater algae are both abundant and diverse. Nearly a century of investigation has shown that all the categories of freshwater algae occur in China and there is wide species richness. It has been shown that the global number of algal species is approximately 40,000, of which about 25,000 are freshwater. Nine thousand species of freshwater algae have been recorded from China (including both those reported upon, and those identified but not yet reported upon). Because, however, there are still many areas which have not yet been surveyed and even though some areas have been surveyed, but not comprehensively, the total number of freshwater algae species in China may exceed 9,000. It is estimated that there may exist between 12,000 to 15,000 species in China (calculated on the basis of 50%～60% of the world total).

The freshwater red and brown algae are relic plants, left over in freshwater during the process of change from sea to land, and almost all of them grow in clean, cool and stable waters, e. g., wells, streams and, especially, springs. Their areals are rather narrowly restricted. Adapted to these environments for a long time, a number of rare and endemic species have evolved. These are scientifically valuable for studying the changes in the earth's environment as well as the evolution of living things. They are rare in other freshwaters of the world. In China, after extensive collecting and investigation for half a century, it has been discovered that some of these algae are recorded only once. There are 12 such species, including Lithoderma zonatum, a freshwater brown alga, and Batrachospermum intortum, B. sinense, Sirodotia sinica, Lermanea siniea, Calogtossa leprieurii var. angusta, freshwater red algae. They should be listed as rare.

(2) Threats to the freshwater algal resources of China

a. Threats to species Though China's freshwater algal resources are numerous, because of change to the natural environment and human activities (especially the development of industry and cities), some rare species have become extinct, or are at the edge of extinction. Among these, the most severely threatened are the freshwater red and brown algae. In recent decades, because of climatic droughts and industrial development, the groundwater of many areas in northern China have been overpumped, resulting in a lowering of the water table and some famous springs have either dried up or face exhaustion. The springs of the “Spring city”, Jinan, in Shandung Province, the Jinci and Niangziguan in Shanxi Province are well-known examples of this. The exhaustion of spring water has led to endemic algae (especially freshwater red algae), which depend upon spring environments, becoming stressed and some are gone. The freshwater brown algae are much rarer and they were last recorded only from the Jialing Jiang River, Chongqing City, Sichuan Province, in the early 1940s. They have since disappeared because of environmental change during the last decades.

In the last ten or more years, along with the rapid economic development of China, many spring resources have been exploited and utilized. Owing to a lack of consciousness, spring environments have not been protected and the freshwater red algae and other organisms living in them are confronted with imminent endangerment and some of them are extinct. For example, the Zhenzhuquan Spring in Pu Kou, near Nanjing City, previously contained luxuriant freshwater red algae, i. e., Batrachospermum ectocarpus and Compsopogon spp.. However, following the development of tourism, the red algae there are close to extirpation. Batracospermum ectocarpum also grows In Jinci, Shanxi Province. When they were investigated in 1994, some still existed, yet, in 1995, due to exhaustion of the spring water, they have disappeared. It is conceivable that for those springs under exploitation (for tourism and for drinking), if not enough attention is paid to their protection, their algae and other spring organisms may be faced with the same misfortune.

In other water bodies where macroalgae live, because of environmental changes induced by human activities, many have already disappeared. For example, in Yang Chen Lake, Jiangsu Province, tracts of Macro Chara plants have died off. The original main algae-desmids-of Dong Lake, near Wuhan, have, sins the 1970s due to increasing eutrophication, been replaced gradually by pollution-enduring, blue-green and chlorococcalous algae. Similar incidents have occurred elsewhere.

b. Species diversity destroyed In normal situations in an ecosystem (especially water ecosystem), the species structure of an algal community maintains a good diversity, i.e., it is species rich, but the number of individuals of each are few and, at this time, the algal community offers excellent ecological benefit. It maintains good water quality, and provides aquatic products. As adverse transformations occur, however, i.e., it becomes severely polluted by heavy-metals and eutrophic, the species diversity of the algal community is destroyed and, at the same time, some species grow more abundantly, leading to the occurrence of harmful marine red tide or freshwater algal blooms. These may block pipelines, cause a deterioration in water quality and diminish fishery resources, even kill fishes with algal toxins. Along with accelerated industrialization and urbanization, environmental problems of this kind occur commonly. The common algae which can form harmful blooms in China are mainly blue-green specie of Microcystis, Anabaena, Anabaenopsis, Oscillatoria ahd Aphanizomenon. They occur extensively in many areas of China, causing serious problems. Prymnesium parvum (Prymnesiophyceae) is also poisonous, and its blooms have caused several poisoning events of breeding fishes. Blooms of diatoms also occur on a large scale as well. During the turn from winter to spring in 1991, the diatom Cyclotella meneghniana occurred in the Han River, Hubei Province and covered an area of 200 km². This diatom bloom seriously influenced the industrial production and livelihood of the residents of Wuhan City and areas along the Han River.

(3) The protection of China's freshwater algae

As mentioned above, although the freshwater algal resources of China are plentiful, they are severely threatened. If no measures are adopted to protect them, many rare species may become extinct. It should be pointed out that, at present, the attention of biodiversity conservationists focuses mainly on larger animals and plants, i. e., charismatic ones, whereas microorganisms, such as algae, are generally neglected. This situation should be changed. While we pay attention to the protection of large species, we should also seek to conserve small micro-organism, such as the algae.