Original paper

Distribution of living (stained) benthic foraminifera (Protista) in the Ohashi River, southwest Japan: a clue to recent faunal change in the Lake Shinji-Nakaumi system

Takata, Hiroyuki; Seto, Koji; Kurata, Kengo; Khim, Boo-Keun

Abstract

The modern distribution of benthic foraminifera in the Ohashi River (southwest Japan) was compared with the prevalent types of bottom substrates. Bottom substrates in the upper ranges of the river were characterized by relatively coarse-grained sediment, low total organic carbon (TOC) and total sulfur (TS) contents, whereas those in the lower ranges were characterized by relatively fine-grained sediment, high TOC and TS contents. Two macrobenthic species, Corbicula japonica and Musculista senhousia, were associated with both the coarse- and fine-grained bottom substrate areas, respectively. Ammonia beccarii forma 1 was the dominant foraminiferal species in the Ohashi River and Haplophragmoides canariensis was common in the middle reaches of the river. Variable salinity and biological substrate disturbance, caused especially by M. senhousia, accounted for this foraminiferal distribution. A transition from the H. canariensis assemblage to the A. beccarii forma 1 assemblage has been found in the 20th century sedimentary record not only in the Ohashi River but also in Lake Shinji. Although the habitat of H. canariensis has not been specified well in the Lake Shinji-Nakaumi system, our result of the modern distribution of benthic foraminifera in the Ohashi River suggests that the faunal transition in Lake Shinji can be explained by the replacement of the dominant foraminiferal species in the Ohashi River.

Keywords

benthic foraminiferasubstrateammonia beccarii forma 1haplophragmoides canariensisfaunal change