Case studies on tropical benthic foraminifera assemblages in coastal marine environments under anthropogenic stress for the investigation of primary controlling factors in their diversity and distribution patterns

Abstract

Benthic foraminifera are found in all types of marine environments, from brackish estuaries to the deep ocean basins. They are invaluable tools in paleoclimatology, paleoceanography, biostratigraphy, and in modern ecological research, where they are used for investigating ecosystem functioning and its interaction with anthropogenic interference. Moreover, structural and numerical analysis of benthic foraminiferal assemblages can provide deeper insights into what combination of environmental variables control their composition with new perspectives to reconstruct past environments. Among realms occupied by benthic foraminifera, tropical ecosystems are extremely productive ones, maintaining biodiversity, protecting coastline, sequestering carbon and providing livelihood to coastal populations. This doctoral thesis looks into the role of benthic foraminifera with the goal of better understanding how these ecosystems function and deteriorate under human impact. This has been accomplished through establishing the benthic foraminiferal inventory of the sites under investigation through careful taxonomical analysis, and studying the structure and numerical parameters of benthic foraminiferal assemblages in relation to physical and chemical data, such as temperature, pH, depth, total dissolved solids (TDS) and potentially toxic elements (PTEs). This investigation resulted in establishing that i. highly saline ocean waters consistently penetrating deep into coastal water bodies (estuaries or lagoons) promote compositionally diverse and species-rich biotas of benthic foraminifera, therefore salinity is the main driving force structuring and separating benthic foraminiferal assemblages, whereas pH and TDS are not observed to have a major controlling effect, ii. the current-, wave-, or anthropogenically induced redistribution of benthic foraminiferal taxa is limited; benthic foraminiferal assemblages may preserve the original community structures and sufficient environmental information that can be useful in biomonitoring and paleoecological studies, iii. the sites impacted by anthropogenic pollution are found to be characterized by specific benthic foraminiferal assemblages and taxa, indicative for enhanced tolerance levels to multiple stressors, providing a repertoire of bioindicators that can assist in future studies focusing on environmental perturbations, iv. using total concentrations of PTEs alone as tools for biomonitoring may not be useful, but especially bio- and non-bioavailable fractions of PTEs should be utilized through correlation with benthic foraminiferal parameters including abundance, species richness and diversity values of foraminiferal assemblages.