The use of testate amoebae in studies of sea-level change: a case study from the Taf Estuary, south Wales, UK

Abstract

Micropalaeontological techniques play an important role in high-resolution studies of sea-level change. Salt-marsh foraminifera are among the most valuable groups of sea-level indicators as their distribution shows a narrow vertical zonation which can be accurately related to former sea level. This paper focuses on testate amoebae (‘thecamoebians’), a closely related group of protozoans which have also been widely reported in salt marshes, but only in low numbers and diversities and only in the size fraction used in foraminiferal analyses (<63 μm). A new preparation technique is described which is based on the analysis of the <63,um fraction using high power light microscopy. This technique is applied to surface sediment samples from a salt marsh in the Taf estuary in south Wales. The results show that small testate amoebae (<63 μm) are much more abundant and diverse in salt-marsh sediments than the larger testate amoebae (>63 μm). Species diversity increases from 2 (>63 prm) to 36 (<63 μm) and the maximum abundance is 65 600 individuals per cm3. The assemblages display a distinct spatial zonation across the marsh surface which appears to be closely related to elevation and to tidal parameters. The surface distribution of the testate amoebae is compared with the distribution of foraminifera and diatoms at the same site. The implications of using <63-μm testate amoebae as a tool for sea-level reconstruction are discussed.