THE BIOLOGY O F WOOD-BORING TEREDINID MOLLUSCS
449
time at the freezing temperature of sea water (-1.4"C) (Roch, 1932).
In the Black Sea the most suitable temperature for Teredo sp. is between
15-25°C (Zvorykin, 1941). Here a temperature of - 1°C is lethal,
at f l to +5"C the animal is moderately active and above 25°C there
is a decline in activity and death occurs at 30 to 38°C. At low temperatures animals may survive 24 days in wood taken out of water
(Zvorykin, 1941). In Japan (Mawatari, 1950) the lethal limit for
teredinids has been fixed around 8-10°C. For T . navalis Imai et al.
(1850) noted that boring ceased at temperatures below 14OC or above
26°C. In the comparative warm waters of Hawaii both adult and larval
shipworms survived 35°C for hours. Cooling from 8 to 0°C caused inactivity but recovery followed when brought back to normal ternperature (Edmondson, 1942). Thus shipworms are generally most
active between 15-30°C. The optimum temperature may be considered
that value at which a certain process goes on fastest. But the temperature for the maximum rate often varies considerably for different
processes within the same organism and also for the same process at
different stages in the life cycle. The optima for the various developmental stages are, however, different from the optimum for the adult.
This is a particularly important factor in the case of the shipworms
because the free-swimming larvae are the infective stage.
The uniformly high temperature of the tropics can stimulate sexual
activity, accelerate development of the gonad, hasten maturity and
shorten the free-swimming larval period. These contribute towards the
production of several spawnings in a single year leading to an almost
continuous settlement of waves of borers which bring about speedy
destruction of timber.
Growth has been considered as the consequence of assimilated food
not diverted to other purposes such as respiration or muscular activity
(Moore, 1966). Loosanoff and Nomejko (1949) have demonstrated a
relationship between the growth rate of Ostrea virqinica and temperature, there being an optimum temperature above and below which
growth decreases. There are cases on record of geographical variation
in size in which temperature is apparently a controlling factor. Nevertheless, it is not clear whether the regions characterized by the larger
sizes are areas of rapid growth or of long continued slow growth. There
is indeed, a general impression that larger forms tend to be found in
colder waters.
As early as 1860, Jeffreys noted that specimens, probably of Teredo
meqotara, from Greenland were twice the size of those found along the
British shores and T. philippi was found to be larger round the British
coasts than in southern localities. He also observed that T . norveqica,
449
time at the freezing temperature of sea water (-1.4"C) (Roch, 1932).
In the Black Sea the most suitable temperature for Teredo sp. is between
15-25°C (Zvorykin, 1941). Here a temperature of - 1°C is lethal,
at f l to +5"C the animal is moderately active and above 25°C there
is a decline in activity and death occurs at 30 to 38°C. At low temperatures animals may survive 24 days in wood taken out of water
(Zvorykin, 1941). In Japan (Mawatari, 1950) the lethal limit for
teredinids has been fixed around 8-10°C. For T . navalis Imai et al.
(1850) noted that boring ceased at temperatures below 14OC or above
26°C. In the comparative warm waters of Hawaii both adult and larval
shipworms survived 35°C for hours. Cooling from 8 to 0°C caused inactivity but recovery followed when brought back to normal ternperature (Edmondson, 1942). Thus shipworms are generally most
active between 15-30°C. The optimum temperature may be considered
that value at which a certain process goes on fastest. But the temperature for the maximum rate often varies considerably for different
processes within the same organism and also for the same process at
different stages in the life cycle. The optima for the various developmental stages are, however, different from the optimum for the adult.
This is a particularly important factor in the case of the shipworms
because the free-swimming larvae are the infective stage.
The uniformly high temperature of the tropics can stimulate sexual
activity, accelerate development of the gonad, hasten maturity and
shorten the free-swimming larval period. These contribute towards the
production of several spawnings in a single year leading to an almost
continuous settlement of waves of borers which bring about speedy
destruction of timber.
Growth has been considered as the consequence of assimilated food
not diverted to other purposes such as respiration or muscular activity
(Moore, 1966). Loosanoff and Nomejko (1949) have demonstrated a
relationship between the growth rate of Ostrea virqinica and temperature, there being an optimum temperature above and below which
growth decreases. There are cases on record of geographical variation
in size in which temperature is apparently a controlling factor. Nevertheless, it is not clear whether the regions characterized by the larger
sizes are areas of rapid growth or of long continued slow growth. There
is indeed, a general impression that larger forms tend to be found in
colder waters.
As early as 1860, Jeffreys noted that specimens, probably of Teredo
meqotara, from Greenland were twice the size of those found along the
British shores and T. philippi was found to be larger round the British
coasts than in southern localities. He also observed that T . norveqica,