THE USE OF TESTATE AMEBAS IN STUDIES OF SEA-LEVEL CHANGE - A CASE-STUDY FROM THE TAF ESTUARY, SOUTH WALES, UK

Micropalaeontological techniques play an important role in high-resolu tion studies of sea-level change. Salt-marsh foraminifera are among th e most valuable groups of sea-level indicators as their distribution s hows a narrow vertical zonation which can be accurately related to for mer sea level. This paper focuses on testate amoebae ('thecamoebians') , a closely related group of protozoans which have also been widely re ported in salt marshes, but only in low numbers and diversities and on ly in the size fraction used in foraminiferal analyses (>63 mu m). A n ew preparation technique is described which is based on the analysis o f the <63 mu m fraction using high power light microscopy. This techni que is applied to surface sediment samples from a salt marsh in the Ta f estuary in south Wales. The results show that small testate amoebae (<63 mu m) are much more abundant and diverse in salt-marsh sediments than the larger restate amoebae (>63 mu m). Species diversity increase s from 2 (>63 mu m) to 36 (<63 mu m) and the maximum abundance is 65 6 00 individuals per cm(3). The assemblages display a distinct spatial z onation across the marsh surface which appears to be closely related t o elevation and to tidal parameters. The surface distribution of the r estate amoebae is compared with the distribution of foraminifera and d iatoms at the same site. The implications of using <63-mu m testate am oebae as a tool for sea-level reconstruction are discussed.