very brackish water was bctwccn 1% aiid 15 ppt, while a Ralinity of
22.5 ppt was the upper limit.
When oysters that had developed gonads a t a salinity of 27 ppt
were used as parents, the optimal salinity for growth of their larvae,
after they had reached straight-hinge stage, was 17.5 ppt. Good
growth was also recorded a t a salinity of 15 ppt, but at 12.5 ppt growth
was appreciably slower, although some larvae grew to metamorphosis.
At 10 ppt growth was practically at a standstill and it is doubtful
that any larvae could reach setting stago a t this salinity. The older
the larvae, however, the better they withstood the salinity of 10 ppt.
Larvae that were reared almost to setting stagc: a t our normal salinity
of about 27 ppt continued to grow and even metamorphosed when
transferred to a salinity of only 10 ppt.
Davis (1958) also showed that the optimal salinity for development
of eggs of &I. mercenaria of Long Island Sound was about 27.5 ppt.
No normal larvae developed at salinities of 17.5 ppt or lower. The
upper salinity limit for development of clam eggs was 35 ppt, but only
an occasional normal larva developed a t {,hat concentration of ualt.
Straight-hinge clam larvae grew reasonahly well a t 17.5 ppt and
many reached metamorphosis, but at 15 p1)t none of them reached
that stage, although some lived for 10 or more days and showed a
slight increase in size. At 12.5 ppt straight-hinge clam larvae showed
no growth and all were dead by the loth day.
As can be seen from this brief comparison, eggs and larvae of C. virginica can normally develop and grow to metamorphosis in a much
lower salinity than those of M . mercenaria. Undoubtedly, using
present methods of cultivation of larvae, similar studies will soon be
performed on other species of bivalves and prove to be as informative
and useful as those reported in the recent article by Davis and Ansell
(1962) on development of eggs and growt$ of larvae of 0. edulia in
water of different salinities.
H. Effects of turbidity o n eg:p and larvae
One of the least studied factors of molluscan environments is that of
turbidity (Loosanoff and Tornmers, 1948 ; ,Imgensen, 1949 ; Loosanoff,
1962a). A review of the literature in this field (Jarrgensen, 1960)
shows that even though some work has been performed on adult
mollusks, until the recent coritributionv of Ilavis (1‘360, and unpublished), virtually nothing was known of thr: ability of bivalve eggs to
develop or larvae to survive in turbid waters. Daviu employed a
rotating wheel, to which culture vessels were attached, to maintain
turbidity a t definite constant levels. The turbidity-creating subdances
22.5 ppt was the upper limit.
When oysters that had developed gonads a t a salinity of 27 ppt
were used as parents, the optimal salinity for growth of their larvae,
after they had reached straight-hinge stage, was 17.5 ppt. Good
growth was also recorded a t a salinity of 15 ppt, but at 12.5 ppt growth
was appreciably slower, although some larvae grew to metamorphosis.
At 10 ppt growth was practically at a standstill and it is doubtful
that any larvae could reach setting stago a t this salinity. The older
the larvae, however, the better they withstood the salinity of 10 ppt.
Larvae that were reared almost to setting stagc: a t our normal salinity
of about 27 ppt continued to grow and even metamorphosed when
transferred to a salinity of only 10 ppt.
Davis (1958) also showed that the optimal salinity for development
of eggs of &I. mercenaria of Long Island Sound was about 27.5 ppt.
No normal larvae developed at salinities of 17.5 ppt or lower. The
upper salinity limit for development of clam eggs was 35 ppt, but only
an occasional normal larva developed a t {,hat concentration of ualt.
Straight-hinge clam larvae grew reasonahly well a t 17.5 ppt and
many reached metamorphosis, but at 15 p1)t none of them reached
that stage, although some lived for 10 or more days and showed a
slight increase in size. At 12.5 ppt straight-hinge clam larvae showed
no growth and all were dead by the loth day.
As can be seen from this brief comparison, eggs and larvae of C. virginica can normally develop and grow to metamorphosis in a much
lower salinity than those of M . mercenaria. Undoubtedly, using
present methods of cultivation of larvae, similar studies will soon be
performed on other species of bivalves and prove to be as informative
and useful as those reported in the recent article by Davis and Ansell
(1962) on development of eggs and growt$ of larvae of 0. edulia in
water of different salinities.
H. Effects of turbidity o n eg:p and larvae
One of the least studied factors of molluscan environments is that of
turbidity (Loosanoff and Tornmers, 1948 ; ,Imgensen, 1949 ; Loosanoff,
1962a). A review of the literature in this field (Jarrgensen, 1960)
shows that even though some work has been performed on adult
mollusks, until the recent coritributionv of Ilavis (1‘360, and unpublished), virtually nothing was known of thr: ability of bivalve eggs to
develop or larvae to survive in turbid waters. Daviu employed a
rotating wheel, to which culture vessels were attached, to maintain
turbidity a t definite constant levels. The turbidity-creating subdances