EFFECTS OB HEATED EFFLUENTS
79
(1959, 1964) in Queen’s Dock, Swansea, ranged from 14-28°C. Though
these ranges appear very similar it does seem that the temperatures in
Queen’s Dock were taken rather farther away from the outfall than those
in Cavendish Dock. Moreover, in contrast to Queen’s Dock, temperatures in Cavendish Dock periodically fell to near ambient sea temperatures owing to intermittent working by the power station, so perhaps
the heating in Queen’s Dock was more prolonged. At any rate the
biological effects of heating in Queen’s Dock were most striking (Naylor,
1959, 1965). In particular, British native species of barnacles were
excluded from the sampling area, either directly owing to the high
temperatures or indirectly through competition with the artificially
introduced subtropical species Balanus amphitrite var. denticulata
Broch (see p. 87). Other evidence that high temperatures appeared to
exclude some species was also apparent in observations in the same area
during a period when the dock was cooler than before, owing to a reduction in power output a t the generating station and a corresponding fall
in the volume of the heated discharge (Naylor, 1965). During that period
the native barnacle Balanus crenutus Brugihre occurred in the dock
alongside B. amphitrite (see Fig. 5), and Elminius modestus Darwin
also extended its range towards the heated effluent. In addition, other
common native species such as Gamrnarus locusta (L.), Aurelia aurita and
Cryptosula were recorded for the first time near the outfall, and it seems
reasonable to suppose that the apparent absence of these native species
during extensive observations when the dock was at its warmest was due
simply to the effects of the heated discharge (Naylor, 1965).
B. Effects upon breeding and general biology
I n addition to the experimental and field evidence that many
species tolerate higher temperatures than those at which they breed
(p. 70), Carcinus maenm is an example of a cold-temperate water
species which appeared to thrive abundantly in an artificially heated
locality without apparently being able to breed there. At a time when
the seasonal range of temperatures in a heated dock was from 14-28°C
Carcinus was found to be very abundant and apparently did not breed,
for specimens moulted throughout the winter months (Naylor, 1965)
when moulting normally ceases and females carry eggs (Naylor, 1962).
Presumably under those conditions of heating the species was recruited
from unheated areas outside the dock, for during a period when dock
temperatures were lowered to near ambient sea temperatures breeding
was observed to take place (Naylor, 1965; Pearce, 1965). Markowski
(1962) also recorded the absence of breeding amongst Carcinus in a
heated dock, but in this case high temperatures may have been less
79
(1959, 1964) in Queen’s Dock, Swansea, ranged from 14-28°C. Though
these ranges appear very similar it does seem that the temperatures in
Queen’s Dock were taken rather farther away from the outfall than those
in Cavendish Dock. Moreover, in contrast to Queen’s Dock, temperatures in Cavendish Dock periodically fell to near ambient sea temperatures owing to intermittent working by the power station, so perhaps
the heating in Queen’s Dock was more prolonged. At any rate the
biological effects of heating in Queen’s Dock were most striking (Naylor,
1959, 1965). In particular, British native species of barnacles were
excluded from the sampling area, either directly owing to the high
temperatures or indirectly through competition with the artificially
introduced subtropical species Balanus amphitrite var. denticulata
Broch (see p. 87). Other evidence that high temperatures appeared to
exclude some species was also apparent in observations in the same area
during a period when the dock was cooler than before, owing to a reduction in power output a t the generating station and a corresponding fall
in the volume of the heated discharge (Naylor, 1965). During that period
the native barnacle Balanus crenutus Brugihre occurred in the dock
alongside B. amphitrite (see Fig. 5), and Elminius modestus Darwin
also extended its range towards the heated effluent. In addition, other
common native species such as Gamrnarus locusta (L.), Aurelia aurita and
Cryptosula were recorded for the first time near the outfall, and it seems
reasonable to suppose that the apparent absence of these native species
during extensive observations when the dock was at its warmest was due
simply to the effects of the heated discharge (Naylor, 1965).
B. Effects upon breeding and general biology
I n addition to the experimental and field evidence that many
species tolerate higher temperatures than those at which they breed
(p. 70), Carcinus maenm is an example of a cold-temperate water
species which appeared to thrive abundantly in an artificially heated
locality without apparently being able to breed there. At a time when
the seasonal range of temperatures in a heated dock was from 14-28°C
Carcinus was found to be very abundant and apparently did not breed,
for specimens moulted throughout the winter months (Naylor, 1965)
when moulting normally ceases and females carry eggs (Naylor, 1962).
Presumably under those conditions of heating the species was recruited
from unheated areas outside the dock, for during a period when dock
temperatures were lowered to near ambient sea temperatures breeding
was observed to take place (Naylor, 1965; Pearce, 1965). Markowski
(1962) also recorded the absence of breeding amongst Carcinus in a
heated dock, but in this case high temperatures may have been less