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Ecosystem/Bras d'Or Lake
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What is MSX?
Known as “Multinucleated Sphere X,” or Haplospordium nelsoni, MSX is a single-celled Protozoan parasite that causes extensive tissue damage in oysters. It first attacks the oyster’s gills, then moves on to the digestive system and eventually infiltrates the entire body. MSX-infected oysters in advanced stages of the disease appear thin and watery-looking, but are not dangerous for human consumption.

It is not known how the MSX parasite is transmitted from oyster to oyster, although it is strongly suspected that it is spread by a water-borne intermediate host. The disease appears to single out the American oyster species. Pacific oysters, thought to be the original carriers of the parasite, do not experience its devastating effects. MSX first appeared in Delaware Bay in 1957, and spread to oyster populations in Chesapeake Bay in 1959. Since that time, outbreaks have occurred in Long Island Sound and along the coast of Maine. The 2002 Bras d’Or outbreak was the first incidence of MSX in Canadian waters.

Outbreaks of MSX appear to be related to higher water temperatures and salinity levels. Researchers have found that the disease can be suppressed, but not fully eradicated, in waters with less than 10 parts per thousand salinity and less than 20 degrees Celsius. Following acute MSX outbreaks, oysters begin to develop natural resistance, and mortality rates go down.
While halting the transfer of MSX-infected oysters to non-infected areas is the first step in preventing the spread of the parasite, scientists are working to prevent further outbreaks by establishing a brood-stock of disease-resistant oysters.

MSX Oyster Misery

For Bras d’Or oyster growers, the Lakes’ connection with the sea has proved to be a mixed blessing. While their brackish inland waters are ideal for oyster aquaculture, their susceptibility to ocean-borne diseases and bio-invaders is having devastating consequences. In the fall of 2002, tests confirmed that the Lakes’ $1 million commercial oyster industry had been hit by MSX, a microscopic parasite that kills up to 95% of the oysters that it infects. The parasite is not harmful to humans.
It is thought that the parasite has been carried into the Bras d’Or Lakes by cargo ships travelling from Baltimore, a U.S. port in Chesapeake Bay where outbreaks of MSX are common. The original Bras d’Or MSX infection has been traced to Little Narrows, in the Lakes’ St. Patrick’s Channel, where ocean-going bulk carriers service a gypsum loading facility.
While it is possible that the MSX parasite may be attached to the hulls of the vessels, it is more likely that it is contained in ballast water carried by the ships to increase their stability. Although the International Maritime Organization recommends that low-salinity ballast water, potentially rich in bio-invading organisms, be exchanged in high-salinity open ocean water, some ships continue to discharge their ballast in the Bras d’Or Lakes. With its constricted marine openings and weak currents, the flushing rate of the Lakes is extremely low, and organisms discharged into their sluggish waters are likely to linger.
The spread of the MSX disease to Cape Breton has highlighted the ecological and economic consequences of unregulated ballast water discharge and the need for more stringent Canadian ballast water regulations. Those concerned with the health of the Bras d’Or ecosystem are also worried about the potential of ocean-going ships to spread dermo, another water-borne parasite that threatens not only oysters, but all other species of shellfish.
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