THE UTILITY OF FORAMINIFERA AND EDNA FROM MANGROVE ENVIRONMENTS IN PENINSULA MALAYSIA TO RECONSTRUCT RELATIVE SEA LEVEL

Microfossil assemblages like foraminifera are used as proxies to constrain vertical uncertainties in reconstructions of relative sea-level (RSL) change in intertidal environments such as mangrove forests. However, these proxies have poor preservation in these tropical environments. In this study, we present a new approach to integrate environmental DNA (eDNA) analysis to enhance RSL reconstruction in a mangrove environment. The advancement of molecular technology allows for the simultaneous characterization of multiple organisms using their genetic material present in the environment. Leveraging this innovation, we conducted a comprehensive investigation in the Matang Mangrove Forest Reserve located in the western Peninsula Malaysia.

Our sampling strategy included surface samples across a transect extending from the mudflat to the interior mangrove as a modern analog. Additionally, we extracted approximately a 3 m type core from the mangrove to investigate the continuous record of foraminifera and eDNA in relation to sea-level fluctuation over time. The type core stratigraphy revealed intertidal marine mud overlain by mangrove peat with organic content ranging from 30 to 60%.

The foraminiferal assemblages found in the type core were well preserved and dominated by typical agglutinated taxa. In parallel with the foraminifera test analysis, the eDNA analysis revealed an average of 46,921 sequences that represented 170 amplicon sequence variants (ASVs). The dominant ASVs were assigned to monothalamous taxa, followed by Robertinida taxa and Rotaliida taxa. Notably, the eDNA analysis detected the genetic presence of marine foraminiferal species, such as Quinqueloculina sp., within the type core, even in the absence of foraminifera tests. This result highlights the capability of eDNA analysis to fill critical gaps in traditional foraminifera-based RSL reconstructions.

In conclusion, the integration of eDNA analysis with traditional foraminiferal tests represents a transformative leap in the field of RSL reconstructions. The recovery and analysis of eDNA preserved in the mangrove environment provide an innovative and promising tool for reconstructing past RSL records. By combining eDNA data with other sea-level indicators, researchers can improve the reliability and accuracy of past sea-level reconstructions across various time scales and locations.