The energetic cost of Perkinsus marinus parasitism in oysters: quantification of the thioglycollate method.
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A quantitative method for counting Perkinsus marinus hypnospores is described. Using the method, Mackin's commonly used 0-5 point scale of infection intensity can be shown to be exponential. From general relationships for oysters and protozoa, the impact of P. marinus at varying infection intensities on the oyster's energy budget can be estimated. Mortality, decreased growth and decreased fecundity in infected oysters, as described in the literature, can be explained by a reduction in the oyster's available energy by P. marinus production and respiration. Because smaller oysters expend proportionally less energy on respiration, the net productivity (growth and reproduction) of larger oysters should be more severly affected by P. marinus at a given infection intensity than smaller oysters.