Dispersal potential of neritic benthic foraminifera in the coastal areas of the Japanese Islands and its application to paleoenvironmental studies

Abstract

In this study, we evaluated the dispersal potential of both modern and fossil benthic foraminifera in lagoon and bay environments in the Japanese Islands. Our investigations of living (stained) benthic foraminifera in Maizuru Bay (central Japan) revealed complicated lateral distributions and high temporal variation among common benthic species. Benthic foraminiferal communities in bay environments are often characterized by strong lateral trends in species richness due to frequent fluctuations in the salinity and/or dissolved oxygen content of the hypolimnion. However, our results do not show the existence of similar trends in Maizuru Bay. In fact, the dispersal of opportunistic species during intense coastal winter mixing events may account for this complexity in species diversity and evenness. Sediment trap and plankton tow observations in Lake Nakaumi (southwestern Japan) imply that benthic foraminifera utilize suspended organic matter aggregates as mobile substrates for passive dispersal. Furthermore, we examined three horizons of high fossil benthic foraminiferal abundance in the Aso-kai Lagoon (central Japan) dating to ca. AD 1070, 1400, and 1570, which were nearly coincident with coastal mixing events that were likely caused by enhanced East Asian winter monsoons. Many of the neritic benthic foraminifera in our study region appear to possess high dispersal potential, suggesting that the distribution of opportunistic benthic foraminifera may be useful in inferring the past status of the East Asian winter monsoon.