Dynamic of Virioplankton Abundance and Its Environmental Control in the Charente Estuary (France)

Abstract

The Charente River provides nutrient- and virus-rich freshwater input to the Marennes Oléron Basin, the largest oyster-producing region in Europe. To evaluate virioplankton distribution in the Charente Estuary and identify which environmental variables control dynamic of virioplankton abundance, five stations defined by a salinity gradient (0-0.5, 0.6-5, 13-17, 20-24, and higher than 30 PSU) were surveyed over a year. Viral abundance was related to bacterioplankton abundance and activities, photosynthetic pigments, nutrient concentration, and physical parameters (temperature and salinity). On a spatial scale, virus displayed a decreasing pattern seaward with abundance ranging over the sampling period from 1.4x10(7) to 20.8x10(7) viruses mL-1 making virioplankton the most abundant component of planktonic microorganisms in the Charente Estuary. A good correlation was found between viral and bacterial abundance (rs=0.85). Furthermore, bacterial abundance was the most important predictor of viral abundance explaining alone between 66% (winter) and 76% (summer) of viral variability. However, no relation existed between viral abundance and chlorophyll a. Temporal variations in viral distributions were mainly controlled by temperature through the control of bacterial dynamics. Spatial variations of viral abundance were influenced by hydrodynamic conditions especially during the winter season where virioplankton distribution was entirely driven by mixing processes.

Genetic Optimization of Artificial Neural Networks to Forecast Virioplankton Abundance from Cytometric Data

“…Although the lack of correlation between these two variables a seasonal behavior of virioplankton seems to emerge. Seasonality in virioplankton has been previously reported [62,63] but our data suggest a close relationship with upwelling process. The lack of correlation may be explained by the low sampling frequency or due to the sample size.…”

In situ structuring of virioplankton through ­bacterial exoenzymatic activity: interaction with phytoplankton

“…Samplings were performed monthly from January to December 2007 at high tide, during periods of medium tidal coefficient (≈60) at 1 northern station located in the external part of the Charente River estuary (45°59' 16.7'' N, 1°10' 0.7'' W, 'Stn E' previously monitored by Auguet et al [2005] and by Ory et al [2010]); in February, sampling was performed closer to the mouth of the estuary (45°59' 5.06'' N, 1°06' 32'' W), because bad weather prohibited sampling at Stn E.…”

“…Mineral and organic seston were assessed by filtering 200 to 500 ml of water, depending on the turbidity, under gentle vacuum pressure (GF/F Whatman filters; Auguet et al 2005).…”

“…In Marennes Oléron Bay (France), previous studies on pelagic microbial organisms and the control of their dynamics highlighted a link between virus abundance and chlorophyll a (chl a) concentration (Ory et al 2010) and described chl a biomass as a significant factor driving the variability of bacterial activities (secondary production and exoenzymatic activities; Auguet et al 2005). By analyzing a new dataset collected during a 1 yr survey in the mesotrophic coastal ecosystem of the Marennes Oléron Bay (MOB), the present study addresses viral assemblage structuring.…”

Virioplankton Abundance in Trophic Gradients of an Upwelling Field

“…However, the factors influencing the dynamics of viral abundance in aquatic environments might be dependent upon complex interactions of both abiotic factors such as pressure, redox conditions, temperature, light effects, and biotic like host abundance, host metabolic rate, viral supply (2,23,46).…”