AME 48:27-34 (2007)  -  doi:10.3354/ame048027

ABSTRACT: We tested the hypothesis that viral production is limited by nutrient availability in oligotrophic subtropical surface waters of the South Pacific. Nutrient (C, N, P) addition experiments were conducted at 2 stations (Stn SX18, 39°60’S, 169°60’W; Stn SX22, 19°60’S, 169°60’W) to examine the responses of viral production (³H-thymidine incorporation) and related variables in bottle-contained surface waters. At Stn SX18, viral production was enhanced in bottles amended with N and C with concomitant increases in bacterial production and growth, suggesting that both viral and bacterial production were co-limited by N and C. At Stn SX22, additions of N accelerated viral production with no consistent response of bacterial production, which might be an indication that prophage production was induced due to the alleviation in N limitation of host bacteria. In both experiments, nutrient-induced increases in viral production were not accompanied by increases in viral abundance, suggesting a possibility that viral production was balanced by loss. Our results suggest that viral production is limited by the availability of N or N+C in subtropical waters of the South Pacific, implying that viruses affect the mode of nutrient-induced changes in bacterial production and microbial trophic transfers in oligotrophic oceanic waters.

KEY WORDS: Viruses · Viral production · Nutrient limitation · Oligotrophic surface waters · South Pacific subtropical gyre