The Spatial Distribution of Perkinsus Marinus, a Protozoan Parasite, in Relation to its Oyster Host (Crassostrea Virginica) and an Ectoparasitic Gastropod (Boonea Impressa)

Perkinsus marinus, a protozoan parasite of oysters, is an important cause of oyster mortality in the Gulf of Mexico and along the south-eastern coast of the United States (Hofstetter, 1977; Quick & Mackin, 1971). Infections are patchily distributed on many reefs, often with uninfected oysters adjacent to infected oysters. The primary mechanism of transmission from one oyster to another is through the water (Ray, 1954; Mackin, 1962; Andrews, 1965). Because dilution rapidly reduces the number of infective elements below the dosage required to initiate new infections (Andrews, 1979), transmission is most efficient over very short distances and declines rapidly within a few metres of the source.