84
E. NAYLOR
heated discharges should be avoided in areas of low oxygen concentration unless compensatory measures can be taken. Freshwater fish are
known to show reduced toleration of high temperatures in lowered
oxygen tensions (Downing and Merkens, 1957 ; Alabaster and Wellcomme, 1962) and the marine serpulid Hydroides norvegica (Gunnerus)
settles less abundantly in harbour areas where oxygen concentrations
are low (Reish, 1961), thus no doubt avoiding polluted areas. Another
possible side effect is the reduced tolerance of toxic substances such as
might be discharged in or alongside heated effluents. This has been
demonstrated mainly for freshwater organisms by a number of authors
(Ministry of Health, 1949 ; Cairns and Scheier, 1958, 1962 ; Doudoroff
and Katz, 1953 ; Hynes, 1960). The inter-dependence of several types
of pollution, including heat, is also illustrated by the work of Resig
(1960) (see p. 77), and also by Milne (1940). The latter author showed
increases in abundance of Jaera albifrons Leach in areas of the intertidal
zone of the Aberdeenshire Dee which were affected by effluents from a
food factory and from a power station. The relative effects of the two
sources of pollution were not investigated.
In estuaries, apart from the interplay of temperature and the factors
mentioned above, the effects of heating may also extend to changes in
the osmoregulatory capacity of the organisms concerned. However,
though the combination of temperature and salinity is of basic importance (Kinne, 1960, 1964), opinions vary as to the precise effects
which are to be expected. Pearse and Gunter (1957) review this subject
and conclude that osmoregulation is facilitated by higher temperatures,
which may be one reason to account for the abundance of organisms
in tropical estuaries compared with those in cold-temperate regions.
On the other hand Kinne (1963) concluded that in general the osmoregulatory capacity of a given species appears to be greatest at or just
below optimum temperatures and to decrease in supra-normal temperatures. At any rate, in practice it seems that estuarine forms are more
tolerant of heated effluents than marine species (see p. 68).
There appear to be few observations on the effects of heat upon
marine and estuarine plants and microorganisms. Most fixed marine
algae are said to be eurythermal (Pruvot, 1896) and have even wider
ranges of distribution than their ability to reproduce would indicate
(Setchell, 1920). In freshwater localities too, it is reported that thermal
pollution does not effect plant communities (Rees, 1964), but Hynes
(1960) has recorded the occurrence of an immigrant flowering plant
species Vallisneria spiralis L. near heated effluents in freshwater. In
addition, effects upon the growth of various stream algae have been
demonstrated by Cairns (1956). He showed that diatoms were most
E. NAYLOR
heated discharges should be avoided in areas of low oxygen concentration unless compensatory measures can be taken. Freshwater fish are
known to show reduced toleration of high temperatures in lowered
oxygen tensions (Downing and Merkens, 1957 ; Alabaster and Wellcomme, 1962) and the marine serpulid Hydroides norvegica (Gunnerus)
settles less abundantly in harbour areas where oxygen concentrations
are low (Reish, 1961), thus no doubt avoiding polluted areas. Another
possible side effect is the reduced tolerance of toxic substances such as
might be discharged in or alongside heated effluents. This has been
demonstrated mainly for freshwater organisms by a number of authors
(Ministry of Health, 1949 ; Cairns and Scheier, 1958, 1962 ; Doudoroff
and Katz, 1953 ; Hynes, 1960). The inter-dependence of several types
of pollution, including heat, is also illustrated by the work of Resig
(1960) (see p. 77), and also by Milne (1940). The latter author showed
increases in abundance of Jaera albifrons Leach in areas of the intertidal
zone of the Aberdeenshire Dee which were affected by effluents from a
food factory and from a power station. The relative effects of the two
sources of pollution were not investigated.
In estuaries, apart from the interplay of temperature and the factors
mentioned above, the effects of heating may also extend to changes in
the osmoregulatory capacity of the organisms concerned. However,
though the combination of temperature and salinity is of basic importance (Kinne, 1960, 1964), opinions vary as to the precise effects
which are to be expected. Pearse and Gunter (1957) review this subject
and conclude that osmoregulation is facilitated by higher temperatures,
which may be one reason to account for the abundance of organisms
in tropical estuaries compared with those in cold-temperate regions.
On the other hand Kinne (1963) concluded that in general the osmoregulatory capacity of a given species appears to be greatest at or just
below optimum temperatures and to decrease in supra-normal temperatures. At any rate, in practice it seems that estuarine forms are more
tolerant of heated effluents than marine species (see p. 68).
There appear to be few observations on the effects of heat upon
marine and estuarine plants and microorganisms. Most fixed marine
algae are said to be eurythermal (Pruvot, 1896) and have even wider
ranges of distribution than their ability to reproduce would indicate
(Setchell, 1920). In freshwater localities too, it is reported that thermal
pollution does not effect plant communities (Rees, 1964), but Hynes
(1960) has recorded the occurrence of an immigrant flowering plant
species Vallisneria spiralis L. near heated effluents in freshwater. In
addition, effects upon the growth of various stream algae have been
demonstrated by Cairns (1956). He showed that diatoms were most