important role in marine communities and, like sponges and bryozoans, often provide a habitat as well as food for other invertebrates and fish. Most important in this respect are the reef-building corals which provide the basis of one of the most productive marine ecosystems in the world. Coral reefs play a number of important roles. They protect the coastline from erosion by wave action; they support fisheries of major importance to many subsistence economies; and they are often the nursery grounds for species of commercial importance (68,75). The reefs are becoming increasingly important as a tourist attraction. SCUBA diving is now a popular sport, and many countries, such as the Philippines, are gearing their tourist industry to attract and cater for divers and snorkellers (25). Even in temperate waters, sea anemones and soft corals can occur locally in large numbers, where their influence on the ecology of the area must be considerable (5). Cnidarians have a number of important uses to man. Black and red corals (see reviews) have been used traditionally as medicines, and jellyfish were used in China for treatment of high blood pressure and bronchitis (If). Many species have been found to contain compounds of potential value in modern medicine. Antimicrobial substances occur in various gorgonian corals and antitumour compounds have been found in Hawaiian zoantharians. Aequorin, the bioluminescent protein present in the jellyfish Aequorea aequorea glows in the presence of calcium or strontium and is sensitive enough to enable detection of minute fluctuations in calcium concentrations in biological fluids. Calcium changes in man often reflect cellular malfunctions and aequorin may prove useful in diagnosing cardiac irregularities and other disease processes (3). Prostaglandins have been isolated from the gorgonian Plexaura homomalla (13). An extract of the sea anemone Rhodactis howesi has an anticoagulant factor and the stony coral Porites has been used as a template for artificial bone (13). Anthozoans are ideal subjects for the study of simple nervous systems and work in this field is a major current interest (10). Recent studies of several anemone species indicate that they are capable of exhibiting complicated behaviour patterns and interacting aggressively, a type of behaviour often difficult to discern in invertebrates). Cnidarians are also used as food. For over a thousand years jellyfish have been commercially exploited for food along the coasts of China, 3apan and South Korea. Since 1960 several species, particularly Rhopilema esculentum have been collected in South East Asia for export to China and Japan (If). IRT 1980, over 63 000 tonnes of Rhopilema were landed, mainly in Thailand, but also in the Philippines and Indonesia (11). Stony corals are often used as a building material and for industrial purposes such as the preparation of calcium carbide and cement (6,56,57,58). The main species exploited for these purposes are the slow-growing massive corals such as Porites Favia Favites Leptastrea and Platygyra The smaller branching species such as Acropora Seriatopora and Pocillopora are used for the ornamental coral trade. In the 1970s most of this came from the Philippines (in 1976 over 1800 tonnes were exported, 15 per cent of which went to the U.S.A), but several other countries are involved to a smaller extent (12). The precious and semi-precious corals in the orders Gorgonacea and Antipatharia are used extensively for jewellery (see following reviews). Other precious corals of commercial importance include the gold corals (Gerardia and Primnoa ) and the bamboo corals ( Lepidisis and Acanella ) and there is probably potential for the exploitation of many other deep water gorgonians (30). Sea fans are used as ornaments. Besides Eunicella verrucosa (see review), the Mediterranean species E. cavolinii and E. singularis (29), as well as many tropical species, are collected for this purpose. The hydroids Sertularia and Hydrallmania known as 'white weed, are fished commercially in Germany and irregularly in the U.K. Having been raked-up from the sea bed, they are processed, dyed and used for decorative purposes, mainly in the U.S.A. (7). THREATS TO SURVIVAL Like most marine species, very few cnidarians are likely 22