70
E. NAYLOR
effluents might therefore serve to increase feeding rates in winter and
also increase the growth rates of affected species, as Weymouth (1918)
has shown for crabs and salmon which grew faster and attained greater
size at comparable ages in years when the growing season was warmer
and longer. Kinne (1960) too, has demonstrated that the fish Cyprinodon
macularius Baird and Girard grows fastest from hatching to maturity
a t fairly high temperatures, with growth rates decreasing in the order
of the following temperatures : 30°, 25O, 35O, 20' and 15°C. However, in
Cyprinodon the high growth rates at high temperatures were not
maintained later in the lives of the experimental fish and initially slow
growing individuals at lower temperatures reached a greater final length
and age. This indeed seems to be a fairly general phenomenon since
many marine and brackish-water animals attain a larger final size in
the colder parts of their distributional area (see for example Wimpenny,
1941 ; Sverdrup et al., 1942 ; Gunter, 1957). Some exceptions to this rule
are given by Moore (1958), but in general one might presuppose that
heated effluents would lead to increased initial growth rates and
precocious maturity, resulting in a decrease of adult size and perhaps
shortening of the life cycle of a t least some species.
C. Reproduction
Without entering into a full discussion of the effects of temperature
upon reproduction in marine organisms (see Gunter, 1957) it is of particular relevance here to distinguish between the " vegetative temperature range " and the " reproductive temperature range '' of the organisms
likely to be affected by heated effluents. The fact that many apparently
eurythermal species breed within a narrower range of temperatures
than that which they tolerate as adults (Gunter, 1957 ; Kinne, 1953a,
b,c, 1956a,b,c, 1959; Brett, 1960) makes it clear that survival of
animals at temperatures simulating those near heated effluents does not
preclude the possibility that the species may be prevented from breeding
in such a locality and therefore would persist there only if continuously
recruited from outside. Organisms which have already ,been shown to
grow at temperatures higher than those at which they reproduce include the Pacific salmon (Fig. 4), Gammarus duebeni Liljeborg (Kinne,
1953a,b,c, 1959), Crassostrea virginica Gmelin (Gunter, 1957) and some
hydroid coelenterates (Kinne, 1956c,d,e). Conversely, artificial warming
might encourage the breeding of non-native species in areas which
receive warm water species through the agency of polewards-flowing
currents. Natural occurrences of such non-breeding warm water
immigrants are reported in the Bay of Fundy (Huntsman and Reid,
E. NAYLOR
effluents might therefore serve to increase feeding rates in winter and
also increase the growth rates of affected species, as Weymouth (1918)
has shown for crabs and salmon which grew faster and attained greater
size at comparable ages in years when the growing season was warmer
and longer. Kinne (1960) too, has demonstrated that the fish Cyprinodon
macularius Baird and Girard grows fastest from hatching to maturity
a t fairly high temperatures, with growth rates decreasing in the order
of the following temperatures : 30°, 25O, 35O, 20' and 15°C. However, in
Cyprinodon the high growth rates at high temperatures were not
maintained later in the lives of the experimental fish and initially slow
growing individuals at lower temperatures reached a greater final length
and age. This indeed seems to be a fairly general phenomenon since
many marine and brackish-water animals attain a larger final size in
the colder parts of their distributional area (see for example Wimpenny,
1941 ; Sverdrup et al., 1942 ; Gunter, 1957). Some exceptions to this rule
are given by Moore (1958), but in general one might presuppose that
heated effluents would lead to increased initial growth rates and
precocious maturity, resulting in a decrease of adult size and perhaps
shortening of the life cycle of a t least some species.
C. Reproduction
Without entering into a full discussion of the effects of temperature
upon reproduction in marine organisms (see Gunter, 1957) it is of particular relevance here to distinguish between the " vegetative temperature range " and the " reproductive temperature range '' of the organisms
likely to be affected by heated effluents. The fact that many apparently
eurythermal species breed within a narrower range of temperatures
than that which they tolerate as adults (Gunter, 1957 ; Kinne, 1953a,
b,c, 1956a,b,c, 1959; Brett, 1960) makes it clear that survival of
animals at temperatures simulating those near heated effluents does not
preclude the possibility that the species may be prevented from breeding
in such a locality and therefore would persist there only if continuously
recruited from outside. Organisms which have already ,been shown to
grow at temperatures higher than those at which they reproduce include the Pacific salmon (Fig. 4), Gammarus duebeni Liljeborg (Kinne,
1953a,b,c, 1959), Crassostrea virginica Gmelin (Gunter, 1957) and some
hydroid coelenterates (Kinne, 1956c,d,e). Conversely, artificial warming
might encourage the breeding of non-native species in areas which
receive warm water species through the agency of polewards-flowing
currents. Natural occurrences of such non-breeding warm water
immigrants are reported in the Bay of Fundy (Huntsman and Reid,