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Disturbance of shallow-marine seafloor ecosystem by the 2011 tsunami

Posted on June 27, 2013

Huge tsunami waves have a severe impact on shallow marine ecosystems. To elucidate the ecological impact of a tsunami on the nearshore zone, data must be obtained on the seafloor environment and benthic animals under pre- and post-event conditions. However, it is extremely difficult to investigate conditions prior to an event, as megathrust earthquakes and associated tsunami are only predictable with low precision.

Photographs of underwater field survey (above) and seafloor at a sampling station in Funakoshi Bay, northeastern Japan (below). These photographs were taken before the tsunami (left, September 2010) and after the tsunami (middle, September 2011; right, September 2012), respectively. Note the complete demise of the sand dollar Scaphechinus mirabilis (black objects on seafloor) after the tsunami. The disc of this echinoderm is approximately 5 cm in diameter. Ripple spacing in middle and right photographs is 5–10 cm. © Koji SEIKE.

Photographs of underwater field survey (above) and seafloor at a sampling station in Funakoshi Bay, northeastern Japan (below). These photographs were taken before the tsunami (left, September 2010) and after the tsunami (middle, September 2011; right, September 2012), respectively. Note the complete demise of the sand dollar Scaphechinus mirabilis (black objects on seafloor) after the tsunami. The disc of this echinoderm is approximately 5 cm in diameter. Ripple spacing in middle and right photographs is 5–10 cm. © Koji SEIKE.

Researchers at the University of Tokyo’s Atmosphere and Ocean Research Institute carried out underwater field surveys on Otsuchi and Funakoshi bays, northeastern Japan before the tsunami (September 2010) and after the tsunami (September 2011 and September 2012), providing a rare opportunity to evaluate the impact of the tsunami on shallow marine seafloor topography, sediments, and megabenthos assemblages.

The researchers documented episodic changes in topography and grain-size composition that occurred on the seafloor after the tsunami. Some benthic animals disappeared after the 2011 tsunami, synchronous with changes in the seafloor environment. This indicates that the 2011 tsunami severely impacted the megafaunal assemblage in the soft bottoms of the ria coasts. In addition, it was found that the reestablishment of some benthic animal populations began within 18 months of the tsunami disturbance.

This research was published in the online journal PLOS ONE on 8 June 2013.

Source: University of Tokyo

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