DAO prepress abstract  -  doi: 10.3354/dao01910

ABSTRACT: The protozoan Perkinsus marinus is considered the most important pathogen of Crassostrea virginica causing high mortality in natural and farmed oysters on the Atlantic coast of the U.S. In Mexico no serious P. marinus epizootic have been reported. This study describes the current state of P. marinus prevalence in Terminos Lagoon (México) associated with environmental factors including salinity, temperature, ammonium, nitrate, nitrite, silica and phosphorus. In addition, the association of physiological (hemocyte density, protein concentration) and immunological (lysozyme, agglutination) parameters with the infection were studied. The prevalence was significantly different among seasons with mean values of 70%, 23% and 7% in the dry (February - May), rainy (June - September) and north-wind (October - January) seasons respectively. Only light infection intensity (Mackin scale value < 1) was observed. Prevalence of P. marinus was associated with seasonal salinity, phosphorus and silica variations. The comparison of the oyster health demonstrates that the rainy and north-wind seasons as stressful periods. Redundancy analysis (RDA) showed that only 34% of the variation in seasonal P. marinus prevalence was explained by protein concentration (21%), lysozyme (12%), and agglutination (1%). Overall, the data suggest that freshwater input associated with high nutrient concentrations during the rainy and north-wind seasons have a strong negative effect on P. marinus prevalence and also influence the oysters’ physiology. It is probable that this seasonal stress was responsible for the absence of an epizootic event in Terminos Lagoon.