Quaternary marine molluscan assemblage around Thoothukudi, India and its implications

Abstract

Live-dead (LD) fidelity is a measure used to assess how well the composition of dead faunal assemblages reflects the composition of living communities. It helps determine how accurately death assemblages preserve ecological signals over time. The live-dead fidelity of marine molluscan assemblages has been extensively used to interpret paleoecological patterns over time. Various factors, such as time averaging, taphonomic alteration, and post-mortem transportation, can impact LD fidelity. The movement of shells after death, whether within or beyond their original environments, plays a key role in altering the spatial fidelity of molluscan assemblages. This study evaluates molluscan (bivalve) fossil assemblage in relation to the compositional fidelity of contemporary molluscan (bivalve) live and dead assemblages. The fossil bivalve assemblage from the Velayudhapuram (Holocene) was compared to live and dead assemblages of the adjacent areas, the Tuticorin group (includes four islands, namely Kariyachalli, Vilanguchalli, Kasuwari, and Vaan) and Vellapatti, revealing little resemblance between fossil and live-dead species composition. While the live and dead assemblages are relatively similar in terms of richness and species composition (both proportional and rank), the fossil assemblage shows significant differences in most of these measures compared to the other two assemblages. Our results suggest that post-mortem processes, such as within/out of habitat transportation, potentially triggered by events such as tropical cyclones or tsunamis, are the main factors leading to the poor fidelity of the fossil assemblage.