Temporal changes of ostracode assemblages and anthropogenic pollution during the last 100 years, in sediment cores from Hiroshima Bay, Japan

Temporal changes of ostracodes during the last 100 years observed in three sediment cores from Hiroshima Bay, the Seto Inland Sea, Japan, provide valuable information about influences on ostracodes caused by anthropogenic pollution. This is the first detailed report of historical records of the relationship between ostracodes and pollution established from core samples drilled in the polluted inner bay. At least 38 ostracode species were identified from 40 samples. Based on biofacies, the density of ostracodes and the faunal structure, it is elucidated that industrialization combined with the effects of the second world war caused a decrease in the density and a increase in the equitability of ostracodes, and that anthropogenic pollution caused a simplification of ostracode assemblages in Hiroshima Bay. The response of two particular ostracode species to anthropogenic pollution is also demonstrated. Callistocythere alata was sensitive and Bicornucythere bisanensis has a strong resistance for anthorogenic pollution in ostracode species. Thus, the relative frequencies of these two ostracodes can be used as an indication of such pollution. We discuss the limitations of using recent ostracode assemblages in the analysis of the palaeoenvironment, resulting from the changes induced by anthropogenic pollution during the last 100 years.