First report of lytic and lysogenic viral production rates in the vicinity of fish farms (Mediterranean Sea)

Abstract

The vital role of viruses in organic matter recirculation has been rarely studied in the coastal zone and never before in aquaculture areas. In this study, we examine for the first time viral lytic and lysogenic production in the vicinity of fish farms in the Mediterranean Sea. Viral production rates were determined based on the viral reduction approach at two impacted stations (including two downstream distances from cages, i.e. 50 and 100 m, and various depths in the water column, i.e. from the surface down to 50 m) and one control site. We highlight that lytic production rates were significantly higher at 50 and 100 m distances from the cages compared to the control. Maximum levels (up to 1.1 × 107 released virus-like particles mL−1 h−1) were seen at the bottom waters of the impacted sites. Interestingly, lytic production was significantly correlated with the concentrations of chlorophyll a, phaeophytin and particulate organic phosphorus, confirming the role of primary producers in fuelling prokaryotic, thus viral activity too. On the other hand, lysogenic production was not correlated with any environmental variable examined here, and did not differ between stations. We propose that viruses, acting in parallel to grazers and dilution processes, may lead to extensive “disappearance” of suspended particulate matter that is produced due to nutrient additions near fish cages. Further, we provide insights into the possibly-involved mechanisms of this viral activity.