EFFEU!L'S OF HEATED EFFLUENTS
7s
closely related species of molluscs from different tidal levels, and all
support the view that temperature acclimatization takes place in this
group. Thus, Vernon (1899), Gowanloch (1926), Gowanloch and Hayes
(1926), Henderson (1929) and Broekhuysen (1940) all concluded that
gastropods and lamellibranchs inhabiting lower levels of the shore were
less tolerant of high temperatures than upper shore specimens. More
recently, Evans (1948) was unable to confirm this in some British
species, but that author was able to show differences in thermal
tolerance according to the particular microhabitats of specimens within
any one species.
Amongst other groups there is evidence for acclimatization and
resistance to high temperatures in marine fishes (Doudoroff, 1942,
1945 ; Morris, 1961), so it is clear that a wide variety of marine animals
show considerable powers of temperature compensation. Some exceptions to this general conclusion are given by Fox (1938, 1939), Fox and
Wingfield (1937) and Wingfield (1939), but Berg (1953) recalculated
Fox and Wingfield's data and concluded that of the exceptions which
they listed only the crinoids Antedon petasus (Diibon and Koren) from
West Sweden and A. biJi&a (Pennant) from Plymouth showed no
apparent acclimatization. More recently too, Farmanfarmaian and
Giese (1963) have reported that another echinoderm, Strongylocentrotus
purpuratus Stimpson, showed no acclimatization beyond the upper
limit of its temperature range of 5-23-5"C. Temperatures of 25OC
were found to be lethal and the apparent thermal tolerance of the species
in having a wide geographical distribution seems to be related to a
change of habitat rather than to acclimatization. Whereas the species
is intertidal in the northern part of its range on the Pacific coast of
North America, it is sublittoral on Mexican coasts, presumably owing
to the high average temperatures of the intertidal zone in that locality.
These examples suggest that echinoderms have little power of temperature acclimatization and would therefore be very susceptible to the
temperature change.
I n conclusion the evidence available so far concerning the temperature relationships of marine species suggests that in artificially heated
areas several types of effect could be observed. Cold water stenothermal
forms might be eliminated or they might be incapable of breeding in
the heated locality and would survive only by recruitment from outside. Some more eurythermal species might become warm-adapted by
the process of acclimatization and survive to breed in the heated
locality, perhaps even evolving into separate races or species from native
forms. Also, immigrant warm-water stenothermal species might be
encouraged to breed there.
7s
closely related species of molluscs from different tidal levels, and all
support the view that temperature acclimatization takes place in this
group. Thus, Vernon (1899), Gowanloch (1926), Gowanloch and Hayes
(1926), Henderson (1929) and Broekhuysen (1940) all concluded that
gastropods and lamellibranchs inhabiting lower levels of the shore were
less tolerant of high temperatures than upper shore specimens. More
recently, Evans (1948) was unable to confirm this in some British
species, but that author was able to show differences in thermal
tolerance according to the particular microhabitats of specimens within
any one species.
Amongst other groups there is evidence for acclimatization and
resistance to high temperatures in marine fishes (Doudoroff, 1942,
1945 ; Morris, 1961), so it is clear that a wide variety of marine animals
show considerable powers of temperature compensation. Some exceptions to this general conclusion are given by Fox (1938, 1939), Fox and
Wingfield (1937) and Wingfield (1939), but Berg (1953) recalculated
Fox and Wingfield's data and concluded that of the exceptions which
they listed only the crinoids Antedon petasus (Diibon and Koren) from
West Sweden and A. biJi&a (Pennant) from Plymouth showed no
apparent acclimatization. More recently too, Farmanfarmaian and
Giese (1963) have reported that another echinoderm, Strongylocentrotus
purpuratus Stimpson, showed no acclimatization beyond the upper
limit of its temperature range of 5-23-5"C. Temperatures of 25OC
were found to be lethal and the apparent thermal tolerance of the species
in having a wide geographical distribution seems to be related to a
change of habitat rather than to acclimatization. Whereas the species
is intertidal in the northern part of its range on the Pacific coast of
North America, it is sublittoral on Mexican coasts, presumably owing
to the high average temperatures of the intertidal zone in that locality.
These examples suggest that echinoderms have little power of temperature acclimatization and would therefore be very susceptible to the
temperature change.
I n conclusion the evidence available so far concerning the temperature relationships of marine species suggests that in artificially heated
areas several types of effect could be observed. Cold water stenothermal
forms might be eliminated or they might be incapable of breeding in
the heated locality and would survive only by recruitment from outside. Some more eurythermal species might become warm-adapted by
the process of acclimatization and survive to breed in the heated
locality, perhaps even evolving into separate races or species from native
forms. Also, immigrant warm-water stenothermal species might be
encouraged to breed there.