REARING OF BIVALVE MOLLUSKS
47
bacteria toxic to larvae. Other compounds which, in certain concentrations, probably improve rate of growth of larvae by partially
inhibiting growth of toxic bacteria are acetone and trichlorobenzene
among the organic solvents, Monuron and Fenuron among the weedicides, and Guthion among the insecticides. Davis (1961) appropriately
suggested that, in some phases of shellfish culture, a sufficient concentration of such insecticides as Lindane may be maintained to destroy
all undesirable crustaceans, while not affecting growth of bivalve
larvae or their food organisms.
Our laboratory and field observations have shown that metabolites
released by some microorganisms, especially dinoflagellates, seriously
affect not only adult bivalves (Loosanoff and Engle, 1947), but also
development of their eggs and larvae (Loosanoff et al., 1953). Such
toxicity of external metabolites and their physiological effects on
aquatic organisms have been recognized by many biologists, some of
these studies having been summarized by Lucas (1947, 1961) and
Korringa (1952). More recently, Loosanoff (1955) reported that a
heavy bloom of dinoflagellates in Milford Harbor caused abortion of
embryos and immature larvae of gravid European oysters, 0. edulis.
Davis and Chanley (1956b) found that a dense bloom of dinoflagellates
caused abnormal development of eggs and larvae of the clam, M . mercenaria, and oyster, C . virginica. Under these conditions only a few
developed into shelled veligers. During that summer concentrations
of dinoflagellates in some areas of Milford Harbor were as high aa
300000 cells per ml. Placing eggs of clams or oysters in this water,
even after it was passed through a Millipore filter to remove dinoflagellates, resulted in only a slight increase in the percentage of clam
or oyster eggs that developed normally.
Although we assume that the effectH noted above were due to
external metabolites emitted by dinoflagellates, it is possible that they
were caused by removal from sea water, by these cells, of certain
substances necessary for normal development of clam or oyster eggs
and larvae. Another possibility is that the presence of a certain substance, favoring rapid growth of dinoflagellates and preventing normal
development of larvae, was simultaneously responsible for both
phenomena.
F. Effects of temperuture on cggs and larvae
Certain observations and experiments devoted to studies of effects
of sudden and extensive changes in temperature on eggs and larvae
of several bivalves have already been described in the preceding section.
47
bacteria toxic to larvae. Other compounds which, in certain concentrations, probably improve rate of growth of larvae by partially
inhibiting growth of toxic bacteria are acetone and trichlorobenzene
among the organic solvents, Monuron and Fenuron among the weedicides, and Guthion among the insecticides. Davis (1961) appropriately
suggested that, in some phases of shellfish culture, a sufficient concentration of such insecticides as Lindane may be maintained to destroy
all undesirable crustaceans, while not affecting growth of bivalve
larvae or their food organisms.
Our laboratory and field observations have shown that metabolites
released by some microorganisms, especially dinoflagellates, seriously
affect not only adult bivalves (Loosanoff and Engle, 1947), but also
development of their eggs and larvae (Loosanoff et al., 1953). Such
toxicity of external metabolites and their physiological effects on
aquatic organisms have been recognized by many biologists, some of
these studies having been summarized by Lucas (1947, 1961) and
Korringa (1952). More recently, Loosanoff (1955) reported that a
heavy bloom of dinoflagellates in Milford Harbor caused abortion of
embryos and immature larvae of gravid European oysters, 0. edulis.
Davis and Chanley (1956b) found that a dense bloom of dinoflagellates
caused abnormal development of eggs and larvae of the clam, M . mercenaria, and oyster, C . virginica. Under these conditions only a few
developed into shelled veligers. During that summer concentrations
of dinoflagellates in some areas of Milford Harbor were as high aa
300000 cells per ml. Placing eggs of clams or oysters in this water,
even after it was passed through a Millipore filter to remove dinoflagellates, resulted in only a slight increase in the percentage of clam
or oyster eggs that developed normally.
Although we assume that the effectH noted above were due to
external metabolites emitted by dinoflagellates, it is possible that they
were caused by removal from sea water, by these cells, of certain
substances necessary for normal development of clam or oyster eggs
and larvae. Another possibility is that the presence of a certain substance, favoring rapid growth of dinoflagellates and preventing normal
development of larvae, was simultaneously responsible for both
phenomena.
F. Effects of temperuture on cggs and larvae
Certain observations and experiments devoted to studies of effects
of sudden and extensive changes in temperature on eggs and larvae
of several bivalves have already been described in the preceding section.