Map of the study area and sampling stations.

<p>The striped area represents tsunami inundation. Open circles represent sampling stations (O-1 to O-5 in Otsuchi Bay; F-1 to F-5 in Funakoshi Bay). ICRC: International Coastal Research Center, Atmosphere and Ocean Research Institute, the University of Tokyo. The map inset shows the epicenter of the 2011 M9.0 Tohoku-Oki earthquake and the study site (black arrow).</p

Seafloor photographs from representative sampling stations.

<p>Left, middle, and right were taken in September of 2010, 2011, and 2012, respectively. The plastic pipe provides a scale and is 2 cm in diameter. <b>a–c</b>: Seafloor at station O-2. Note the demise of large burrow openings since 2011 (after the tsunami). <b>d–f</b>: Seafloor at station O-3. The muddy seafloor changed to a sandy bed after the tsunami, and then reverted to a muddy bed. <b>g–i</b>: Seafloor at station F-3. Note the decrease in the number of fecal mounds produced by the lugworm <i>Arenicola brasiliensis</i> after the tsunami. The fecal mounds are approximately 10 cm in diameter. Ripple spacing in h and i is approximately 20 and 10 cm, respectively. <b>j–l</b>: Seafloor at station F-4. Note the complete demise of the sand dollar <i>Scaphechinus mirabilis</i> (black objects on seafloor) after the tsunami. The disc of the echinoderm is approximately 5 cm in diameter. Ripple spacing in k and l is 5–10 cm.</p

Results of megabenthos sampling in Otsuchi Bay.

<p>Large solid circles represent the presence of a benthic animal in a sampling station, while small open circles represent absence. Left, middle, and right maps represent the distribution of each species in September of 2010, 2011, and 2012, respectively. Note that the distribution succession differs among the species.</p

Results of megabenthos sampling in Funakoshi Bay.

<p>Large solid circles represent the presence of a benthic animal in a sampling station, while small open circles represent absence. Left, middle, and right maps represent the distribution of each species in September of 2010, 2011, and 2012, respectively. Note that the distribution succession differs among the species.</p

Environmental parameters of seafloor for each sampling station and date.

<p>Environmental parameters of seafloor for each sampling station and date.</p

Summary of published information on magabenthos in the study sites.

<p>Summary of published information on magabenthos in the study sites.</p

Map of the study area showing the locations of sampling sites.

<p>Map of the study area showing the locations of sampling sites.</p

Grain-size distributions, concentrations of ¹³⁷Cs, CT images, photographs, and columnar sections for the cores.

<p>Layer 1, the upper part of the cores, was bioturbated. Layer 2, the sediments between the base of Layer 1 and the erosional surface (the coarse-grained bed), shows well-defined physical sedimentary structures such as parallel laminations. Layer 3, the sediments beneath the erosional surface, show neither physical sedimentary structures nor obvious bioturbation structures. nd: not detected. m: mud. s: sand. g: gravel.</p

Close-up view of the burrows produced by <i>Echinocardium cordatum</i>.

<p>(A) CT image of the upper part of core F-2. (B) Sketch of (A). The transverse width of the <i>E</i>. <i>cordatum</i> burrows is ~3 cm.</p

Temporal change in test width of <i>Echinocardium cordatum</i> in Funakoshi Bay before and after the 2011 tsunami.

<p>The <i>E</i>. <i>cordatum</i> population disappeared in 2011 and began to recolonize from early 2012. The test width had reached the same size as before the tsunami by September 2014, when the sediment cores were collected.</p