[OANNES Foro] Concentration of Escherichia coli in sediments as an indicator of the sanitary status of oyster aquaculture sites

[Mario Cabrejos]

Journal of Applied Ichthyology
Volume 24 Issue 6, Pages 678 - 684
Published Online: 27 Oct 2008

Concentration of Escherichia coli in sediments as an indicator of the sanitary status of oyster (Crassostrea virginica) aquaculture sites
R. Sonier 1 , E. Mayrand 2 , A. D. Boghen 1andrew.boghen en umoncton.ca, M. Ouellette 3 and V. Mallet 4 
 1 Département de biologie, Université de Moncton, Moncton NB E1A 3E9, Canada;  2 Département de biologie, Université de Moncton, Campus de Shippagan, Shippagan ;   3 Department of Fisheries and Oceans, Gulf Fisheries Centre ;   4 Département de chimie/biochimie, Université de Moncton, Moncton, NB, Canada 

ABSTRACT
The objective of the study was to determine whether there are differences in Escherichia coli counts in relation to seasonal and/or spatial distribution patterns in a conditional shellfish-growing zone located in the Richibucto estuary, New Brunswick, Canada. E. coli concentrations in surface water, sediments, suspended and bottom cultured American oysters (Crassostrea virginica) were determined. Contamination levels in water were significantly lower than in sediments, bottom and suspended cultured oysters (P < 0.01; P < 0.05, P < 0.01, n = 303, respectively). No significant difference in fecal contamination was observed between suspended and bottom cultured oysters (P > 0.05, n = 303). Seasonal variations (temporal) had a significant influence on fecal coliform contamination of all components (P < 0.01, n = 303, linear model). E. coli concentration levels were as much as ten times higher in sediments than in water. Furthermore, results suggest that E. coli concentration levels in sediments are a more reliable indicator of the sanitary status of a grow-out operation than E. coli levels in water. Considering only sampling dates when contamination levels in oysters exceeded the established threshold of 230 MPN, less than 50% of the cases were predicted by water contamination while as many as 89.9% of the samples were predicted by sediment contamination using the proposed threshold of 75 MPN per 100 g. This paper emphasizes the importance of acknowledging the significant role sediments play in the dynamics of contamination by E. coli in areas that are currently exploited or are being considered for shellfish aquaculture. The presence of E. coli in sediments should not be overlooked as an integral factor in assessing the environmental sanitary status.