Foraminiferal assemblages response to anthropogenic influence and parallel to decadal sea-level changes over the last 70 years in Lake Kugushi, Fukui Prefecture, southwest Japan

The sea-level rise over the last 70 years is clearly indicated by two kinds of foraminiferal assemblages: the appearance of marine species in the 1950s and 1970s, and the development of a brackish assemblage preferring eutrophic water from the 1980s onward. The latter is an assemblage dominated by Trochammina hadai, which is common in coastal lagoons with a well developed halocline and highly eutrophied argillaceous substrates. Based on the different response of these foraminiferal assemblages to sea-level rise, the most recent sea-level rise is driven by a mechanism unlike those in the 1970s and 1950s. The thermal expansion of seawater will lead to coastal lagoons that will be more stagnant and eutrophic, with little exchange of coastal marine water.