3. UNDERSTANDING SYMBIONTS OF MARINE MOLLUSCS
11
reviewed in detail by Korringa (1952) and hence need not be given in
detail here. In brief, the heaviest blow dealt to the industry in Europe
occurred during 1920 and 1921, when large numbers of dead oysters
appeared with relative suddenness in France, England, Germany,
Denmark and the Netherlands. Many natural oyster beds were wiped
out and have yet to recover. The cause has never been satisfactorily
determined. In 1919, another serious mortality of Ostrea edulis occurred
in the Mar Piccolo near Taranto, Italy (Cerruti, 1941s). In the New
World, Needler (1941) and Needler and Logie (1947) have reported the
devastating mortality of the American oyster, Crassostrea virginica,
which was initiated during 1914 in the waters of Prince Edward Island,
Canada. The cause of this vast mortality remains uncertain, but the
designation " Malpeque disease " has been coined for identification.
This designation was borrowed from Malpeque Bay, Prince Edward
Island, where the f i s t deaths were noticed. During subsequent years,
the mortality spread to neighboring oyster beds and eventually
destroyed shellfisheries in all of the principal producing areas of Prince
Edward Island, reaching Enmore River in 1933 and the important
Charlottetown area in 1936.
During the 1930s another devastating mortality of Ostrea edulis
occurred in Dutch waters and lasted until the 1940s. The cause has been
investigated by Korringa (1947, 1951c) who believes that a fungus was
responsible. Furthermore, he has expressed the opinion that the fungus
may have reached the oysters from the shells of Cardium and Crepidula
that had invaded the oyster beds in large numbers during this period.
The oyster industry along the Atlantic and Gulf coasts of the
United States has suffered two severe blows during the last two decades
and which are continuing. Crassostrea virginica along the south
Atlantic and Gulf coasts are being killed by a disease caused by a
fungus named Dermocystidium marinurn* by Mackin et al. (1950).
Even more severe, oysters in both the Chesapeake and Delaware
Bays and adjacent waters, two major producing areas, were, and are,
continuing to be killed off by a sporozoan originally designated as
MSX and recently named Minchinia nelsoni by Haskin et al. (1966).
In addition to these major mortalities, numerous others have been
reported and several zooparasites have been found in oysters and other
commercially important marine pelecypods. Although the cause-andeffect relationship has not been established in most cases, there is
a legitimate concern over such parasites as possible lethal agents.
Another reason for the interest of shellfish biologists in parasites
of marine molluscs lies in the possibility that certain parasites of
fungal genus Labyrinthornyxa as L. marina.
* Dermocyatidium marinum has been transferred by Mackin and Ray (1900) to the
11
reviewed in detail by Korringa (1952) and hence need not be given in
detail here. In brief, the heaviest blow dealt to the industry in Europe
occurred during 1920 and 1921, when large numbers of dead oysters
appeared with relative suddenness in France, England, Germany,
Denmark and the Netherlands. Many natural oyster beds were wiped
out and have yet to recover. The cause has never been satisfactorily
determined. In 1919, another serious mortality of Ostrea edulis occurred
in the Mar Piccolo near Taranto, Italy (Cerruti, 1941s). In the New
World, Needler (1941) and Needler and Logie (1947) have reported the
devastating mortality of the American oyster, Crassostrea virginica,
which was initiated during 1914 in the waters of Prince Edward Island,
Canada. The cause of this vast mortality remains uncertain, but the
designation " Malpeque disease " has been coined for identification.
This designation was borrowed from Malpeque Bay, Prince Edward
Island, where the f i s t deaths were noticed. During subsequent years,
the mortality spread to neighboring oyster beds and eventually
destroyed shellfisheries in all of the principal producing areas of Prince
Edward Island, reaching Enmore River in 1933 and the important
Charlottetown area in 1936.
During the 1930s another devastating mortality of Ostrea edulis
occurred in Dutch waters and lasted until the 1940s. The cause has been
investigated by Korringa (1947, 1951c) who believes that a fungus was
responsible. Furthermore, he has expressed the opinion that the fungus
may have reached the oysters from the shells of Cardium and Crepidula
that had invaded the oyster beds in large numbers during this period.
The oyster industry along the Atlantic and Gulf coasts of the
United States has suffered two severe blows during the last two decades
and which are continuing. Crassostrea virginica along the south
Atlantic and Gulf coasts are being killed by a disease caused by a
fungus named Dermocystidium marinurn* by Mackin et al. (1950).
Even more severe, oysters in both the Chesapeake and Delaware
Bays and adjacent waters, two major producing areas, were, and are,
continuing to be killed off by a sporozoan originally designated as
MSX and recently named Minchinia nelsoni by Haskin et al. (1966).
In addition to these major mortalities, numerous others have been
reported and several zooparasites have been found in oysters and other
commercially important marine pelecypods. Although the cause-andeffect relationship has not been established in most cases, there is
a legitimate concern over such parasites as possible lethal agents.
Another reason for the interest of shellfish biologists in parasites
of marine molluscs lies in the possibility that certain parasites of
fungal genus Labyrinthornyxa as L. marina.
* Dermocyatidium marinum has been transferred by Mackin and Ray (1900) to the