Ill

52 59

Plastic Sanitary Paper

Metal Polystyrene Glass

35 39

Wood

Rubber Cloth

Figure 10.1 Comparison of marine debris recorded from British beaches in 1994-96 by 'Beachwatch'. This project, organized by the Marine

Conservation Society with sponsorship from Reader's Digest, uses volunteers to monitor and clean up litter on Britain's beaches. (From Pollard and Parr (1996) Beachwatch '96 nationwide beach-clean and survey report by kind permission of the Marine Conservation Society.)

to improve. A beach covered in plastic is very unpleasant for us but it is often fatal to marine life. Animals can be poisoned or starve after eating plastic; or they can become entangled and trapped. Classic examples include air-breathing turtles, seals and cetaceans which are drowned by floating fishing net and plastic sheeting. Turtles, especially the leatherback, eat plastic bags mistaking them for jellyfish. The bags make them feel full so that they stop feeding properly. In addition chemical plasticizers may poison them. Even birds and fish may be poisoned in this way. In the English Channel, dead cod have been found killed by ingesting plastic cups thrown overboard from cross-Channel ferries. Tiny floating plastic pellets are mistaken for fish eggs or other plankton and eaten. Near some industrial centres in New Zealand, up to 100 000 pellets have been found on one square metre of beach.

Artificial reefs

Some types of rubbish can be beneficial to marine life. Divers often report blennies and other small fish living in tin cans and glass jars. Parts of the sea floor in the vicinity of large ports are littered with clinker and ash dating from the time when steamships were powered by coal-burning furnaces. Clinker, tyres and many other objects on the sea-bed can encourage the development of a larger and more diverse population by providing a range of cavities and holes offering protection and concealment. Experiments are being carried out in many parts of the world in deliberately constructing artificial reefs using a variety of materials. The aim is often to encourage a greater variety and abundance of fish life for the benefit of local fishermen or divers (Collins and Jensen, 1996). Shipwrecks are well known for their ability to act as a focus for marine life and new wrecks soon become colonized. Some fish seem to be directly attracted to large objects such as wrecks and will move in well before the wreck can provide anything other than shelter. Groupers have been observed to move into a wreck in the Arabian Gulf only days after it sank and many miles from the nearest rocky area or reef (Dipper, 1991).

The question of dumping de-commissioned oil platforms at sea has become topical recently, as many platforms in the UK are reaching the end of their useful life. Some scientists feel these would make good artificial reefs, whilst others are against the idea. The question of using deep-ocean areas for dumping came to the fore in 1996 with the de-commissioning of the giant Brent Spa platform. Whilst some scientists argued that the deep ocean dumping was an ecologically sound option, others disagreed and public opinion was so strongly against it that disposal on land was finally agreed. The deep-ocean is vast and, in relative terms, sparsely populated by marine organisms. However, water exchange in the depths is extremely slow as are rates of breakdown and decomposition. Deep-sea communities may be easily disrupted since reproductive rates are often very slow. Waste disposal in the deep ocean is discussed by Angel (1996).

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Figure 10.2 Some materials from which artificial reefs may be constructed: (a) scrap tyres securely bound together and weighted; (b) purpose-built Japanese unit made from concrete containing coal fly ash; (c) Taiwanese open structure, coal-ash units designed to attract shoals offish.

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