Spatio-Temporal Variation in Perkinsus olseni Infection in Manila Clam Ruditapes philippinarum in Korean Waters

Abstract

Previous studies have demonstrated that most of Manila clams in Korean waters are infected with Perkinsus olseni, although the level varies spatially and temporally. In 2007, we surveyed P. olseni infection prevalence and intensity in Manila clams in Korean waters collected from 23 locations on the west, south and east coast. The infection prevalence and intensity was determined using RFTM and 2M NaOH digestion. Whole clam tissues were incubated in FTM and the total number of hypnospores were counted and expressed as number of P. olseni cells per gram tissue. Each sampling location was visited twice, in spring (May) and fall (November). The survey indicated that clams from river mouth areas, where salinity ranged 10-20 ppt were free from P. olseni, exhibiting 0% prevalence, regardless of season. The prevalence ranged 80-100% in most of the sampling locations on the west and south, regardless of seasons. The population mean infection intensity of clams from tidal flats on the west and south coast varied 50,000 to 200,000 cells/g tissue in case of light infection, while the intensity ranged 1,000000 to 5,000,000 cells/g tissue in case heavy infection in November. The infection intensity determined in November was significantly higher than May, regardless of sampling locations. The infection intensity was closely related to latitude, bottom type, and density of clams. The infection intensity of clams collected from intea clams in Korean waters collected from 23 locations on the west, south and east coast. The infection prevalence and intensity was determined using RFTM and 2M NaOH digestion. Whole clam tissues were incubated in FTM and the total number of hypnospores were counted and expressed as number of P. olseni cells per gram tissue. Each sampling location was visited twice, in spring (May) and fall (November). The survey indicated that clams from river mouth areas, where salinity ranged 10-20 ppt were free from P. olseni, exhibiting 0% prevalence, regardless of season. The prevalence ranged 80-100% in most of the sampling locations on the west and south, regardless of seasons. The population mean infection intensity of clams from tidal flats on the west and south coast varied 50,000 to 200,000 cells/g tissue in case of light infection, while the intensity ranged 1,000000 to 5,000,000 cells/g tissue in case heavy infection in November. The infection intensity determined in November was significantly higher than May, regardless of sampling locations. The infection intensity was closely related to latitude, bottom type, and density of clams. The infection intensity of clams collected from inte