Production of viruses during a spring phytoplankton bloom in the South Pacific Ocean near of New Zealand

Abstract Lagrangian studies of virus activity in pelagic environments over extended temporal scales are rare. To address this, viruses and bacteria were examined during the course of a natural phytoplankton bloom in the pelagic South Pacific Ocean east of New Zealand. Daily samples were collected in a mesoscale eddy from year days 263–278 (September 19th–October 4th, 2008). The productive bloom transitioned from a diatom to a pico- and nanoplankton-dominated system, resulting in chlorophyll a concentrations up to 2.43 μg L−1. Virus abundances fluctuated c. 10-fold (1.8 × 1010–1.3 × 1011 L−1) over 16 days. The production rates of virus particles were high compared with those reported in other marine systems, ranging from 1.4 × 1010 to 2.1 × 1011 L−1 day−1. Our observations suggest viruses contributed significantly to the mortality of bacteria throughout the bloom, with 19–216% of the bacterial standing stock being lysed daily. This mortality released nutrient elements (N, Fe) that likely helped sustain the bloom through the sampling period. Parametric analyses found significant correlations with both biotic (e.g. potential host abundances) and abiotic parameters (e.g. nutrient concentrations, temperature). These observations demonstrate that viruses may be critical in the extended maintenance of regeneration-driven biological production.