Contemporary foraminiferal distributions of a mangrove environment, Great Barrier Reef coastline, Australia: implications for sea-level reconstructions

Contemporary foraminiferal samples and associated environmental information were collected from Cocoa Creek, a mesotidal fringing mangrove environment on the Great Barrier Reef (GBR) coastline, Australia, to elucidate the relationship of the foraminiferal assemblages with elevation and environment. There is a strong and highly significant relationship between elevation and the foraminiferal assemblages, supporting the intertidal vertical zonation concept, which suggests that the distribution of foraminifera in the intertidal zone is usually a direct function of elevation, with the most important controlling factors being the duration and frequency of subaerial exposure. Multivariate analyses separate the intertidal foraminiferal assemblages into three elevational zones, with Zone I the highest and Zone III the lowest: Zones I and II are dominated by agglutinated species Trochammina inflata and Miliammina fusca, respectively; and Zone III is dominated by calcareous species, notably Ammonia tepida and Elphidium discoidale multiloculum. These assemblage zones are similar to those found in both tropical and temperate intertidal environments. A predictive transfer function has been developed to allow reconstruction of former sea levels for tropical environments, based upon the relationship between foraminiferal assemblage and elevation. Results suggest that a precision of ±0.07 m should be attainable, superior to most similar studies from temperate, mid latitude environments. Our work has produced the first foraminifera-based transfer function for environmental interpretations for tropical Australia, and allows the potential development of a new generation of high-resolution sea-level reconstructions for the post-glacial sequences of the GBR shelf.