Distribution spatio-temporelle d'une population bactérienne allochtone (coliformes thermotolérants) dans un écosystème marin côtier (Bassin de Thau, France)

Abstract

The variation in the levels of thermotolerant coliforms has been measured at various time–space observation scales in a marine coastal ecosystem (Thau pond). The spatial distribution of the bacteria was organized in the ecosystem (observation distance ≈1 km) in the form of either spots or gradients. The latter only appeared after massive drifts from the watershed. A strong local variation (< 1 km) was permanently associated with a broader observation scale. Local variation can develop from rapidly decreasing gradients in the levels of thermotolerant coliforms, starting from the drift points of the watershed. The variation with time was high whatever the observation frequency (monthly, daily, hourly). Monthly sampling usually revealed higher bacterial counts during winter compared with summer. During winter, the daily and hourly degree of variation of the bacterial levels was comparable and the populations were organized according to a linear trend. In summer time, there was a higher degree of variation in the populations and hourly variations can show cyclic trends (diurnal minima and nocturnal maxima). Our results show that privileged sampling scales occur and should be considered when evaluating the impact of environmental parameters (sun exposure, role of the watershed… ) and trying to correlate them. These results also enabled us to define a better sampling strategy for the detection of thermotolerant coliforms in such an ecosystem. Key words: thermotolerant coliforms, marine coastal ecosystem, spatial distribution, variation with time, sampling. [Journal translation]

Distribution and survival of motile Aeromonas spp. in brackish water receiving sewage treatment effluent

“…The bacterial data from spatial sampling were interpreted with the aid of interpolated maps obtained by kriging (29). This method has been previously described and used to analyze the spatial structures of fecal coliforms in the water of both the cove and the whole of Thau Lagoon (25). The temporal statistical analysis was performed by using the programs of the R package (P. Legendre, Departement de Sciences Biologiques, Universite de Montreal, Montreal, Canada), and kriged maps were obtained by using the UNIMAP computer package (European Software Contractors A/S, Lyngby, Denmark) on an IBM 3081 computer (Centre National Universitaire Sud de Calcul, Montpellier, France).…”

The effect of environmental factors on bacterial populations and community dynamics in high rate oxidation ponds

“…Jones (1977) was the first to emphasize the importance of sampling frequency in the study of the relationships between the bacteria and their environment. Lebaron et at. (1990) showed that to analyze the effect of environmental factors on fecal coli forms in a marine coastal ecosystem (Thau lagoon, France), it is necessary to consider a privileged sampling scale.…”

Le REMI, réseau de surveillance de la qualité bactériologique des coquillages du littoral français: premiers résultats

“…Historiquement, I'objectif principal de la surveillance bactériologique des coquillages en France était la salubrité des bivalves pour la consommation humaine (Poggi 1986 Si les eaux conchylicoles de l'étang de Thau sont salubres la majeure partie de l'année, on enregistre des augmentations de la colimétrie des eaux et des coquillages à la suite de fortes pluies (Lebaron et al 1990 (Rhodes et Kator, 1988).…”