EWECTS OP HEATED EETLTTENTS
91
been reported by Iles (1963) and Markowski (1965). Carp, rainbow
trout and salmon all grew very fast in an estuarine dock used as a cooling pond by a power station, and it is suggested that plaice, flounders,
eels and grey mullet might also be profitably introduced (Iles, 1963;
see also Shelbourne 1964). The culture of a North American clam Venus
mercenuria in Britain might also be improved by irrigating the beds
with warm-water effluents from industrial cooling systems (Ansell,
1962, 1963b; Ansell et al. 1964a,b). Another suggestion (Hynes, 1959)
is that cooling ponds, which would normally support only a few surviving native species, could be deliberately stocked with appropriate
warm water species to render them attractive or useful, provided proper control and careful investigation were carried out. Finally, it is
possible that heated effluents might locally ameliorate the effects of
severe winters, which are known to result in a high mortality particularly amongst low latitude species (see Crisp, 1964a). Local commercial
fisheries of oysters, cockles and mussels might benefit in this way.
However, the possibility that algal blooms might become more prevalent in heated areas (see p. 85) is a disadvantage from the shell-fishery
point of view since such blooms usually result in severe mortalities,
particularly amongst filter feeding forms.
V. CONCLUSIONS
Biological effects which have been observed so far in areas affected
by heated discharges include the elimination of some species such as
cool water stenothermal forms (see p. 76), together with possible increase in the abundance of remaining eurythermal species (see p. 81),
perhaps also accompanied by the introduction of immigrant warmwater stenothermal species. The polewards spread of subtropical species
could be facilitated in this way (see p. 72) and there is experimental
(see p. 72) and field evidence (see p. 90) that warm-water species may
become acclimatized to temperate regions by this means. Some forms too
may evolve into warm-water races or even species in heated localities
(see p. 90). Apart from the purely biological aspects of heating several
economic problems are also apparent in that many fouling and boring
species may increase in abundance (see p. 82 and p. 83). Disadvantages
such as these may, of course, be offset by beneficid effects, both from the
amenity point of view (see p. 90) and by the possible local use of heated
effluents to improve the yield of some commercially fished species (see
p. 90).
The effects of heated discharges clearly vary according to whether
the hot water spills into enclosed areas such as docks or estuaries, or
into open areas on the coast. Dissipation of heat is probably greatest
F 2
91
been reported by Iles (1963) and Markowski (1965). Carp, rainbow
trout and salmon all grew very fast in an estuarine dock used as a cooling pond by a power station, and it is suggested that plaice, flounders,
eels and grey mullet might also be profitably introduced (Iles, 1963;
see also Shelbourne 1964). The culture of a North American clam Venus
mercenuria in Britain might also be improved by irrigating the beds
with warm-water effluents from industrial cooling systems (Ansell,
1962, 1963b; Ansell et al. 1964a,b). Another suggestion (Hynes, 1959)
is that cooling ponds, which would normally support only a few surviving native species, could be deliberately stocked with appropriate
warm water species to render them attractive or useful, provided proper control and careful investigation were carried out. Finally, it is
possible that heated effluents might locally ameliorate the effects of
severe winters, which are known to result in a high mortality particularly amongst low latitude species (see Crisp, 1964a). Local commercial
fisheries of oysters, cockles and mussels might benefit in this way.
However, the possibility that algal blooms might become more prevalent in heated areas (see p. 85) is a disadvantage from the shell-fishery
point of view since such blooms usually result in severe mortalities,
particularly amongst filter feeding forms.
V. CONCLUSIONS
Biological effects which have been observed so far in areas affected
by heated discharges include the elimination of some species such as
cool water stenothermal forms (see p. 76), together with possible increase in the abundance of remaining eurythermal species (see p. 81),
perhaps also accompanied by the introduction of immigrant warmwater stenothermal species. The polewards spread of subtropical species
could be facilitated in this way (see p. 72) and there is experimental
(see p. 72) and field evidence (see p. 90) that warm-water species may
become acclimatized to temperate regions by this means. Some forms too
may evolve into warm-water races or even species in heated localities
(see p. 90). Apart from the purely biological aspects of heating several
economic problems are also apparent in that many fouling and boring
species may increase in abundance (see p. 82 and p. 83). Disadvantages
such as these may, of course, be offset by beneficid effects, both from the
amenity point of view (see p. 90) and by the possible local use of heated
effluents to improve the yield of some commercially fished species (see
p. 90).
The effects of heated discharges clearly vary according to whether
the hot water spills into enclosed areas such as docks or estuaries, or
into open areas on the coast. Dissipation of heat is probably greatest
F 2