Fate of benthic invertebrates during seabed liquefaction: Quantitative comparison of living organism body density with liquefied substrate density

Abstract Shaking of the ground caused by earthquakes and wave loading on the seafloor during storms can liquefy seabed sediments, highlighting that seabed ecosystems can be substantially affected by modification of the substrate. To investigate exogenous-forced behavior of organisms in liquefied substrates we measured the body density of benthic organisms including bivalves, gastropods, annelids, and echinoderms collected from coastal areas of Japan, and compared them with the liquefied substrate density. The measured density for most benthic individuals was less than that of the liquefied substrate, suggesting that these species would float upwards in liquefied substrates. In contrast, a few individuals of three species including the corbicula clam ( Corbicula japonica ), Stimpson's hard clam ( Mercenaria stimpsoni ), and the sand dollar ( Scaphechinus mirabilis ) had higher body densities than the density of the liquefied substrate. These heavier benthic invertebrates would be expected to move downward during liquefaction of the substrate. These findings indicate that body density may determine the response of each benthic species to seabed liquefaction, forcing them to move upward or downward depending on their body density.