Abstract
On 11 March 2011, a mega-earthquake followed by a huge tsunami hit a large area of the Pacific coast of Tohoku, Japan, and caused widespread disturbances in marine ecosystems; however, the impacts on virus-bacteria systems have not yet been elucidated. To investigate whether virus-bacteria interactions were affected by the earthquake and tsunami, we analyzed time series data of viral and bacterial abundances in Otsuchi Bay. Data were collected every 2 mo, from July 2011 to September 2015. Bacterial abundance exhibited a recurrent seasonal cycle with high abundance during the warm season. The seasonal trend of viruses generally followed that of the bacteria, yielding an average virus to bacteria ratio (VBR) of 10.8 ± 3.6 (mean ± SD; n = 432). A notable exception was found at the first 2 sampling times (July and September 2011) when the VBR was consistently low, with an average value of 5.9 ± 1.2 (n = 32). The average VBR during these time periods was substantially lower than the VBR observed in the same season of subsequent years. An analysis of the subset of data collected in the warm season of 2011 and 2012 revealed that the viral abundance and VBR were negatively correlated with turbidity. These results support the hypothesis that viruses were scavenged by non-host particles from the resuspended sediments and damaged catchment. The earthquake and tsunami thus exerted a prolonged impact, over several months, on the virus-bacteria dynamics in Otsuchi Bay.
Highlights
On 11 March 2011, a large area of the Pacific coast of Tohoku, Japan, was hit by a mega-earthquake followed by a huge tsunami (Goto et al 2021)
These results indicate that the trophic coupling from primary producers to virus− bacteria systems was tight during the warm season when pico- and nanophytoplankton were abundant
virus to bacteria ratio (VBR) in 2011 were significantly lower than those in subsequent years (Fig. 5B,C). These results suggest that the low VBR in July and September 2011 was primarily due to a significantly lower viral abundance in 2011 compared to the other years, it was partly due to higher bacterial abundance in 2011 compared to 2012
Summary
On 11 March 2011, a large area of the Pacific coast of Tohoku, Japan, was hit by a mega-earthquake followed by a huge tsunami (Goto et al 2021). Previous studies have examined seasonal and interannual variabilities of viral abundance and VBR in coastal marine environments (Li & Dickie 2001, Winget et al 2011). To our knowledge, no studies have examined the responses of virus−bacteria systems to environmental perturbations caused by large earthquakes and tsunamis. The tsunami reached a maximum height of 15.1 m, caused large disturbances to the bottom sediments, destroyed 5600 buildings in the inundated area (6.68 km2), and generated 612 × 103 t of debris (Fukuda et al 2015). The prolonged high turbidity in the bay was likely due to the sediment resuspension caused by the earthquake aftershocks and the loading of particulate materials released from tsunami debris and reconstruction activities (Ikehara et al 2014, Fukuda et al 2015)
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