62
VICTOR L. L O O S A N O W A N D HARRY C. D A V I S
C . virginica are unable to utilize forms having cell walls, such as
Chlorella, older larvae of the same species become able to do so after
they reach a larger size of approximately 110 p.
I n general, these studies have demonstrated several important
points. One of them is that larvae of M. mercenaria can live and grow
to metamorphosis on a very restricted diet, consisting of a single
species of algae, such as Chlorclla, and that unlike larvac of C. virginica,
they can utilize these algae during all stages of clevalopment. Our
conclasions, therefore, disagree with those of Cole ( 1938) who maintained
that bivalve larvae, in general, (lo riot possess the enzymes needed for
digestion of cellulose, of which the cell walls of algae, such as Cklorella,
are made.
As our techniques improved and we were able to evaluate the food
value of different forms of phytoplankton, we found that larvae of
M. mercsnaria can be grown not only on a pure culture of Chlorella,
reaching metamorphosis in some cases in 12 days, but that they
can also be grown to metamorphosis on pure cultures of any one of the
following three flagellates : Chlumydomoitas sp., Chromulina pleiades or
I . galbana. (Davis and Loosanoff, 1953).
Our studies have also shown that organic detritus, at least of the
types tested, cannot be utilized by larvae of clams, M. mercenaria
(Loosanoff et al., 1951), or oysters (Davis, 1953).
Larvae of M. mercenaria seem t o be capable of both mechanical,
or quantitative, and chemical, or qualitative, selectivity in feeding.
They arc athlo to regulate tho amount, of food ingested : ~ n d t h u s survivc:
in heavy conccntrations of food cc:IIs, often containing IWH food in
their stomachs than larvtu: kcJ)t in lighter food conct:ritrationn.
AJ)pari:ntly, clarri larvrrc: w i : tiot rric:rc:ly i i w ( h ~ t t i c d f i ~ t ( I i : r ~ ,
twt ~ O H H C H H
a mccIiruiisrri tiy I Y I C ~ ~ I ~ H
of which th:y can coiitrol the fiJOd intake by
rejecting algal cells, when necessary. However, if kept in heavy concentrations of algae for a long time, the larvae loso this regulating
ability, become choked with food cells and, eventually, die.
We also observed that larvae can select certain food organisms
from a mixture of several forms of phytoplankt,ori. ]+'or c:xample, whcm
given a mixture of Porphyridiurrb SJI. and Chlrlm~~ilortrori,r,.nH HI), Inrvtw
of M. mercenuria ingested the much 1argt:r cells of' Chllnr.?ldi~u)ri,ax,
while rejecting the cells of the smaller Porphyridium (1,oonarioff at d ,
1953).
An important problem faced in connection with cultivatiort of
bivalves was to ascertain the cffects of different, ooiic:c:rit,rRt,iotIH of'
food organisms upon larval survival and rate of growth. 'I'hc first
series of experiments was conducted with larvae of M. mercsn,nria in
VICTOR L. L O O S A N O W A N D HARRY C. D A V I S
C . virginica are unable to utilize forms having cell walls, such as
Chlorella, older larvae of the same species become able to do so after
they reach a larger size of approximately 110 p.
I n general, these studies have demonstrated several important
points. One of them is that larvae of M. mercenaria can live and grow
to metamorphosis on a very restricted diet, consisting of a single
species of algae, such as Chlorclla, and that unlike larvac of C. virginica,
they can utilize these algae during all stages of clevalopment. Our
conclasions, therefore, disagree with those of Cole ( 1938) who maintained
that bivalve larvae, in general, (lo riot possess the enzymes needed for
digestion of cellulose, of which the cell walls of algae, such as Cklorella,
are made.
As our techniques improved and we were able to evaluate the food
value of different forms of phytoplankton, we found that larvae of
M. mercsnaria can be grown not only on a pure culture of Chlorella,
reaching metamorphosis in some cases in 12 days, but that they
can also be grown to metamorphosis on pure cultures of any one of the
following three flagellates : Chlumydomoitas sp., Chromulina pleiades or
I . galbana. (Davis and Loosanoff, 1953).
Our studies have also shown that organic detritus, at least of the
types tested, cannot be utilized by larvae of clams, M. mercenaria
(Loosanoff et al., 1951), or oysters (Davis, 1953).
Larvae of M. mercenaria seem t o be capable of both mechanical,
or quantitative, and chemical, or qualitative, selectivity in feeding.
They arc athlo to regulate tho amount, of food ingested : ~ n d t h u s survivc:
in heavy conccntrations of food cc:IIs, often containing IWH food in
their stomachs than larvtu: kcJ)t in lighter food conct:ritrationn.
AJ)pari:ntly, clarri larvrrc: w i : tiot rric:rc:ly i i w ( h ~ t t i c d f i ~ t ( I i : r ~ ,
twt ~ O H H C H H
a mccIiruiisrri tiy I Y I C ~ ~ I ~ H
of which th:y can coiitrol the fiJOd intake by
rejecting algal cells, when necessary. However, if kept in heavy concentrations of algae for a long time, the larvae loso this regulating
ability, become choked with food cells and, eventually, die.
We also observed that larvae can select certain food organisms
from a mixture of several forms of phytoplankt,ori. ]+'or c:xample, whcm
given a mixture of Porphyridiurrb SJI. and Chlrlm~~ilortrori,r,.nH HI), Inrvtw
of M. mercenuria ingested the much 1argt:r cells of' Chllnr.?ldi~u)ri,ax,
while rejecting the cells of the smaller Porphyridium (1,oonarioff at d ,
1953).
An important problem faced in connection with cultivatiort of
bivalves was to ascertain the cffects of different, ooiic:c:rit,rRt,iotIH of'
food organisms upon larval survival and rate of growth. 'I'hc first
series of experiments was conducted with larvae of M. mercsn,nria in