Thermal pollution changes the seasonality and intensity of 

 migration of a number of benthic invertebrates, the feeding rate (which 

 sometimes decreases, sometimes increases), the growth rate (which 

 increases), the maximum size and size upon achievement of sexual 

 maturity, shell thickness, volume of accumulation of various chemical 

 elements in the body tissues (for example, oysters accumulate an excess 

 of copper, which has a depressing effect on them). 



Thermal pollution has a severe effect on breeding, larval 

 development and reproduction of organisms in the sea and estuaries, 

 particularly benthic invertebrates in the vicinity of the thermal 

 discharge (Davis, 1972; Verwey, 1973; Mileikovsky, 1976). The most 

 usual result of this effect is earlier beginning and longer duration of 

 the periods of breeding and spawning. This picture was observed for 

 benthic invertebrates in regions of thermal discharge of electric power 

 plants along the coasts of England, Wales, Scotland and the USA (Pannell 

 et al., 1962, Naylor, 1965a, b; Adams, 1969; Barnett, Hardy, 1969; 

 Barnett, 1971, 1972). Induction of reproduction out of season has also 

 been noted for marine plants (Wood, Zieman, 1969). The earlier 

 beginning and longer duration of the reproductive and spawning season 

 usually give the species involved certain advantages and increase their 

 competitiveness, although at times the earlier beginning of spawning 

 simply means that some of the fry die because they are hatched too early 

 (Barnett, Hardy, 1969). 



In temperate and cold waters, thermal pollution creates favorable 

 conditions for the reproduction of various intruders from warmer waters 

 (Ansel! , 1963; Raymont, Carrie, 1964; Stubbings, Houghton, 1964; Naylor, 

 1965a, b; Adams, 1969). 



Under the influence of the heating caused by thermal discharge, the 

 duration and time of settlement of pelagic larvae of some forms of 

 benthic invertebrates change (becoming longer for most species), the 

 nature of succession changes, and the settling rate increases. All of 

 this results in the formation of more abundant epi fauna in regions of 

 thermal discharges, and sometimes of infauna as well, than in normal 

 areas. 



3.7 Degree of Harm of Thermal Pollution of Marine Coastal and 

 Estuarine Waters " 



The question arises: what is the specific harm of thermal 

 pollution at its present level of intensity? The data which have been 

 gathered indicate that in most cases, the harmful effect is not very 

 strong, and is manifested in small regions in the immediate vicinity of 

 the discharge of heated water. Based on the fact that the effect of the 

 thermal discharge of the Hunterstone nuclear power plant (Scotland) on 

 the fauna of the Firth of Clyde is quite limited, it has been assumed 

 that in the temperate latitudes, thermal pollution, at today's scale, 

 will have no harmful influence on the marine biota. However, should the 

 volume of thermal pollution increase in the future, unexpected ecologic 

 effects may occur (Barnett, 1971). 



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