REARING O F BIVALVE MOLLUSKS
45
larvae were accidentally left overnight in a small pipette of sea water,
yet they were found alive and healthy the following day.
Recent studies of Davis (1958) have clearly demonstrated that eggs
and larvae of at least some estuarine species, such aa C . virginicu, can
endure sharp changes in salinity. This matter will be discussed more
extensively in the section dealing with the general aspects of changes
in salinity upon development of eggs and larvae.
Studies of effects of turbidity upon eggs and larvae of C . virginicu
(Davis, unpublished) and those of M . mercenaria (Davis, 1960), which
will be discussed later in greater detail, have demonstrated that larvae
of these two species can endure and even continue to grow in water
that is quite turbid. For example, Davis has shown that larvae of
C. virginica may survive for at least 14 days in a concentration of 2 g
of silt per liter of sea water. Such a heavy concentration seldom occurs
in nature.
Fertilized eggs and larvae of many bivalves can also withstand
vigorous mechanical disturbances without ill effects. For example,
to obtain a representative sample of the population from our culture
vessels, the water is strongly agitated by means of a plunger to assure a
homogeneous distribution of larvae. Such relatively rough treatment,
usually performed every day or every second day, does not cause an
increase in mortality or decrease the rate of growth of larvae. Observations on the behavior of larvae in nature also support this conclusion
because, as shown by our studies of plankton samples and by observations on intensity of setting of oysters on natural beds, i t has been
definitely established that strong winds accompanying New England
hurricanes and churning the water of Long Island Sound steadily for
several days do not noticeably diminish larval populations. This was
especially well demonstrated in August 1955, when a marked increase
in intensity of setting of oysters occurred immediately after hurricane
( ( Connie ”. This increase continued for 2 weeks, thus showing that
larvae of all ages survived the hurricane. It is also of interest that
setting of oyster larvae occurred during the hurricane, thus indicating
that strong water turbulence does not easily destroy larvae or seriously
interfere with their metamorphosis.
Recent studies have repeatedly demonstrated the sensitivity of
bivalve larvae to traces of certain substances in the water. These
observations showed that sea water, in which our larval cultures are
grown, sometimes contains substances, so far unidentified, which
determine whether larvae will grow normally (Loosanoff et al., 1951 :
1953). Wilson (1951) found similar differences between natural
sea water collected from widely separated areas of the ocean. We are
45
larvae were accidentally left overnight in a small pipette of sea water,
yet they were found alive and healthy the following day.
Recent studies of Davis (1958) have clearly demonstrated that eggs
and larvae of at least some estuarine species, such aa C . virginicu, can
endure sharp changes in salinity. This matter will be discussed more
extensively in the section dealing with the general aspects of changes
in salinity upon development of eggs and larvae.
Studies of effects of turbidity upon eggs and larvae of C . virginicu
(Davis, unpublished) and those of M . mercenaria (Davis, 1960), which
will be discussed later in greater detail, have demonstrated that larvae
of these two species can endure and even continue to grow in water
that is quite turbid. For example, Davis has shown that larvae of
C. virginica may survive for at least 14 days in a concentration of 2 g
of silt per liter of sea water. Such a heavy concentration seldom occurs
in nature.
Fertilized eggs and larvae of many bivalves can also withstand
vigorous mechanical disturbances without ill effects. For example,
to obtain a representative sample of the population from our culture
vessels, the water is strongly agitated by means of a plunger to assure a
homogeneous distribution of larvae. Such relatively rough treatment,
usually performed every day or every second day, does not cause an
increase in mortality or decrease the rate of growth of larvae. Observations on the behavior of larvae in nature also support this conclusion
because, as shown by our studies of plankton samples and by observations on intensity of setting of oysters on natural beds, i t has been
definitely established that strong winds accompanying New England
hurricanes and churning the water of Long Island Sound steadily for
several days do not noticeably diminish larval populations. This was
especially well demonstrated in August 1955, when a marked increase
in intensity of setting of oysters occurred immediately after hurricane
( ( Connie ”. This increase continued for 2 weeks, thus showing that
larvae of all ages survived the hurricane. It is also of interest that
setting of oyster larvae occurred during the hurricane, thus indicating
that strong water turbulence does not easily destroy larvae or seriously
interfere with their metamorphosis.
Recent studies have repeatedly demonstrated the sensitivity of
bivalve larvae to traces of certain substances in the water. These
observations showed that sea water, in which our larval cultures are
grown, sometimes contains substances, so far unidentified, which
determine whether larvae will grow normally (Loosanoff et al., 1951 :
1953). Wilson (1951) found similar differences between natural
sea water collected from widely separated areas of the ocean. We are