off Tasmania earlier this century (39). In Chile the giant mussel Choromytilus chorus and the gastropod Concholepas concholepas have both been overfished (23). Even cephalopods, a resource under-utilized in many regions, have been overfished in some areas. Catches of cuttlefish in the eastern central Atlantic have declined drastically and the north-west Pacific catches, which still represent 60 per cent of the total world production, have been declining steadily since 1968 (9). Commercial mother-of-pearl species have been over-collected in many areas (18). In Papua New Guinea catches of Trochus niloticus decreased progressively during the first half of this century, until 1956 when regulations were introduced (26). In the Andaman and Nicobar Islands, the introduction of new diving techniques by the Japanese in the 1930s caused rapid depletion of T. niloticus ; whereas in 1933 over 20 shells could be collected in an hour, by 1935 only two or three were found in the same length of time (27). In New Caledonia, populations have been periodically over-collected (13) and by the 1950s there was evidence of serious overfishing in Palau (15). Intensive exploitation has led to the disappearance of the pearl oyster Pinctada margaritifera from some Polynesian atolls (2). There is evidence that the ornamental shell trade is causing depletion of local populations of some of the more popular shells, although it is unlikely to cause the biological extinction of any species (If). Shells have been heavily collected on the Kenyan coast for many years by amateur shell collectors, tourists and commercial operators. This has resulted in the extreme scarcity of large colourful species on the more accessible parts of the coastal reef (1,30). Similar situations are to be found in Guam, Florida, the Seychelles and other regions where tourism has recently become a major industry (31,32,33). In the Philippines certain species are becoming rare (29), particularly the giant clams Tridacna spp. and the Giant Triton Charonia tritonis (see data sheets). Marine species with restricted ranges are particularly susceptible to over -collection. Easter Island and Mauritius have several endemic cowries such as Cypraea cribellum and C. esontropia ; with the growth of tourism, these species could be over-collected (1 1). Cymbiola rossiniana a volute endemic to the south-west coast of New Caledonia, is highly sought after, fetching high prices on the international market and there are fears that it could be over-collected (28). The rapid growth of SCUBA diving as a hobby and the development of new fishing techniques could pose a threat to some species since previously inaccessible populations can now be reached. Certain deep-sea molluscs have always been rare and have fetched high prices on the shell market; for example the Glory-of-the-sea Cone Conus gloriamaris fetched U.S2000 in 196 but it is now being found in comparatively large numbers, particularly in the Philippines, and sells for U.S200-300 (29). Harpa costata is a very valuable, apparently rare species, endemic to Mauritius. Specimens have been collected in considerable numbers in the past (11) but the impact of exploitation on this and similar species is unknown since nothing is known of their ecology and population dynamics. 2. Pollution Very little is known about the effects of pollution on marine molluscs. Oil on the shore and in the intertidal zone can kill molluscs by smothering or poisoning them, and filter feeders and deposit feeders may ingest and accumulate dispersed or segmented oil. Moderate and chronic exposure of bivalves to low concentrations can have an important commercial impact. It has been recognized that there is a need to control pollution from oil and chemicals discharged from ships in Dongonab Bay in the Sudan to prevent damage to Pinctada margaritifera which is cultured in the area (25). Bivalves filter a large volume of water, and ingest hydrocarbons which accumulate, particularly in the fatty tissues, at a faster rate than they are eliminated. However, following the cessation of pollution it is usual for hydrocarbons in the tissues to be reduced to low levels within 30 days. Like many other marine invertebrates, molluscs may be 72