Eastern Oysters were once abundant in Barnegat Bay. 

Oysters

Anatomy

Lifecycle

Why the Decline

Disease

Comeback

Oysters in months without an R

 Eastern Oyster                              Crassostrea virginica

Once plentiful in Barnegat Bay, the Eastern oyster had serious problems with two diseases

MSX and Dermo

These diseases affect oysters but are not harmful to humans

MSX gill infection can be observed within 3 weeks -Death occurs with 2 to 3 weeks.

Dermo may take up to 3 years before the oyster dies.

MSX refers to a disease of oysters caused by the protozoan organism Haplosporidium
nelsoni.

Haplosporidium nelsoni, was originally given the acronym “MSX” because it was observed as a Multinucleated Sphere with unknown affinity (“X”)

Oyster production in Chesapeake and Delaware bays has been severely depressed since the appearance of H. nelsoni in the late 1950s.

Geographical distribution
Infected oysters are found along the east coast of North America from Nova Scotia, Canada to Florida, USA.

H. nelsoni cells usually appear first in gill tissue, indicating that the infective stage is water borne

Effects of the disease include decreased condition (meat quality), reduced reproductive
capacity, and mortality.

Infections of H. nelsoni are rare at salinities below 10 ppt and intensify above 15 ppt

Cooler water temperatures also restrict growth.

Selective breeding has been successful in producing highly resistant strains and the development of resistance through natural selection has been reported in some wild populations subjected to heavy infection pressure.

Management strategies include maintaining oysters at reduced salinities (< 15 ppt) as long as possible.

Dermo disease was first identified as the cause of extensive oyster mortalities nearly fifty ago

It was originally thought to be a fungus and was named Dermocystidium marinum.

Even though subsequent research led to its reclassification as a protozoan parasite Perkinsus marinus in 1978, the disease is still commonly referred to as “Dermo.”

Dermo is  is characterized by the degradation of oyster tissue.

    The image on the left is a healthy oyster

  The image on the right is infected with Dermo

Today P. marinus is prevalent throughout the warm waters of the Gulf of Mexico and southeastern U. S. In recent years its range has extended as far north as southern Maine, in conjunction with high winter temperatures

P. marinus is highly infectious, capable of spreading rapidly throughout a growing area. The disease is transmitted directly from infected to uninfected oysters.

A decrease in growth is usually noted prior to mortality, which is typically between 40%
and 90% after two to three years of exposure.