Soniat TM2010-02-152010-02-151984 198http://hdl.handle.net/1969.3/23104-Twenty-six monthly samples of oysters (Crassostrea virginica ) were collected from Galveston Bay, Ttexas, from May 1979 to September 1981. Percent infection and weighted incidence (WI) of P. marinus were calculated for each monthly sample and factors known to be related to parasitism were measured (oyster length (L) and water temperature (T) and salinity (S). The variability of parasitism within a monthly sample was significantly less than the variation between samples. Highest and lowest values of WI were found during months representing every season of the year. A correlation between WI and S was significant (r = 0.51). Elevated levels of parasitism are known to be associated with high temperature and high salinity. Some summer samples, however, had the lowest WI values recorded, although they were always coupled with salinities below 10 ppt. Likewise, some winter samples (at S > 15 ppt) had high values of WI. Only approximately equals 49% of the variability in WI is explained by the TxS interaction; genetically determined resistance to disease is likely a major source of the unexplained variation. teraction; genetically determined resistance to disease is likely a major source of the unexplained variationASW,Galveston BayCrassostreaCrassostrea virginicaGalveston BayheadlevelsOystersparasitismPerkinsus marinusQ1 01422 Environmental effectsQ1 01484 Species interactions: parasites and diseasesQ1 01583 Shellfish cultureQ3 01583 Shellfish cultureSalinitySalinity effectsShellfishTemperatureTemperature effectsUSAVariabilitywaterwater temperaturewinterCONF