Two epizootic Perkinsus spp. events in commercial oyster farms at Santa Catarina,Brazil

Perkinsus spp. have been detected in various bivalve species from north‐east Brazil. Santa Catarina is a South Brasil state with the highest national oyster production. Considering the pathogenicity of some Perkinsus spp., a study was carried out to survey perkinsosis in two oyster species cultured in this State, the mangrove oyster Crassostrea gasar and the Pacific oyster Crassostrea gigas. Sampling involved eight sites along the state coast, and oyster sampling was collected during the period between January 2013 and December 2014. For the detection of Perkinsus, Ray's fluid thioglycollate medium (RFTM) and histology were used, and for the identification of the species, PCR and DNA sequencing were used. Perkinsus spp. was found by RFTM in C. gigas and C. gasar from São Francisco do Sul. This pathology was also detected in C. gasar from Balneário Barra do Sul both, by RFTM and histology. Perkinsus marinus was identified in C. gigas and C. gasar from São Francisco do Sul and Perkinsus beihaiensis in C. gasar from Balneário Barra do Sul. This is the first report of P. marinus in C. gigas from South America. Results of this preliminary study suggest that both oyster species tolerate the species of Perkinsus identified, without suffering heavy lesions.     

How many soil samples are neccessary to obtain a reliable estimate of mean nitrate concentrations in an agricultural field?

In Germany, field‐average soil NO₃^‐ measurements are used to identify agricultural risks of groundwater pollution and to evaluate the compliance of land users with environmental regulations. In the present study, it was tested at three typical agricultural sites if common practices of soil NO₃^‐ sampling were appropriate to obtain reliable estimates of the mean field NO₃^‐ content in fall. Three sites of 1 ha area were extensively sampled for NO₃^‐. Ordinary statisticial analyses were conducted on the NO₃^‐ data in order to calculate how many samples per ha were required to predict the mean field NO₃^‐ with a given accuracy. Variograms were derived to assess applicability and relevance of ordinary statistical methods for heterogeneous fields. Results from statistical analysis suggest that at two sites common practices of soil NO₃^‐ sampling would have been adequate to obtain estimates of the actual mean field NO₃^‐ content with a sampling error less than 10 kg NO₃^‐‐N ha^—1 at a 95% probability level. At the other site, common practices obviously would have failed because NO₃^‐ contents varied much more spatially. It remains a problem of soil sampling for NO₃^‐ analysis that information on field heterogeneity is frequently not available a priori.