A global problem of today is the large amount of waste in the seas and oceans, primarily plastic waste. It is estimated that every year 1.25 to 2.41 million tons of plastic material is being carried by rivers into the seas and oceans. Waste is a major problem for marine organisms, causing entanglement, choking, strangulation, malnutrition and death. In 1972 the problems caused by microplastics, particles smaller than 5 mm, were first observed. Such particles bind pathogenic microorganisms on to their surface. Increasing quantities of microplastics have been found in the stomachs of fish, and also in shellfish that feed by filtering sea water. Ingested by marine organisms, such plastics may eventually pass through the food web and can end up ingested by humans. In addition, plastic releases chemical compounds whose effect on marine organisms and humans has still not been studied. Many international and state organizations offer solutions through recycling plastic waste, as well as reducing the production of plastic materials and informing the public about the problem.
Juveniles of the fan mussel Pinna nobilis were collected in Mali Ston Bay from October to December 2006. Cages with juveniles were placed at three depths: 1, 3 and 5 m. At the end of a 2-year growth period at 1 m depths, the average length was 244.1 ± 22.9 mm, at 3 m depths, specimens averaged 244.0 ± 25.3 mm, and at 5 m depths, the average length was 231.1 ± 22.5 mm. The average monthly growth of shell length for the total experimental period was 8.7 ± 5.3, 8.4 ± 4.5 and 7.6 ± 4.4 mm, at 1, 3 and 5 m depths respectively.
Bearded horse mussel and Noah's ark shell are sometimes observed to live together in groups. Oxygen consumption, ammonia excretion and clearance rate were investigated on these species under laboratory conditions considering different size of individuals divided into three size groups (less than 25 mm; 25 to 50 mm and larger than 50 mm). Body size of both species significantly influenced oxygen consumption, ammonia excretion and clearance rate of the Noah's ark shell. In both species, respiration and clearance rate decreased with body size while excretion rate increased with body size. For Noah's ark shell groups of 25 to 50 mm and smaller than 25 mm, the atomic ratio between oxygen consumption and ammonium excretion i.e. O:N ratio was detected to be greater than 30. The same applies to a group of the bearded horse mussels smaller than 25 mm. Animals of both species larger than 50 mm have O:N ratio smaller than 30 indicating use of proteins as metabolic substrate, compared to use of lipids and carbohydrates in younger animals.
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