Correlations Between Environmental Conditions Andvibrio Parahaemolyticusorvibrio Vulnificusin Pacific Oysters From New Zealand Coastal Waters

Vibrio parahaemolyticusandVibrio vulnificuscan be found in oysters in coastal environments.Vibrio vulnificuscan induce life-threatening illness when ingested with oysters, whileV. parahaemolyticususually causes self-limiting gastroenteritis. This study investigated correlations between concentrations of theseVibriospecies in Pacific oysters from eight New Zealand coastal regions (2008-2017), and seawater surface temperature (SST), salinity and rainfall. In the pooled data, most (88%) of the oyster samples were collected during summer and autumn. The prevalence ofV. parahaemolyticusandV. vulnificuswas 85% and 15%, respectively.Vibrio vulnificuswas always detected in the presence ofV. parahaemolyticus. Across all regions,V. parahaemolyticusconcentration positively correlated with SST (r(S) = 0.60), but not with salinity (r(S) = -0.01).Vibrio vulnificusconcentration weakly correlated with SST (r(S) = 0.26) and salinity (r(S) = -0.21). Linear and generalised additive models were investigated but none were satisfactory for prediction. Salinity and SST explained < 50% of the variability inV. parahaemolyticusconcentrations, indicating that other environmental or biological factors contributed. When SST, salinity and rainfall 15 days prior to harvesting were investigated for one region, SST was the best pre-harvest indicator for elevated concentrations of bothVibriospecies.