Benthic Foraminifera Assemblages from Shallow-Water Ecosystems

Abstract

Benthic foraminifera have proved to be useful as present and past indicators in aquatic habitats because they are sensitive and react rapidly to environmental changes in various ecosystems. The knowledge of their modern ecology presents a potent assessment of their fossil counterparts regarding paleoenvironmental reconstructions and taxonomy. They provide ample information in the assessment and monitoring of transitional and coastal ecosystems e.g. estuaries, coastal lagoons, deltas and reef environments. These are productive environments in terms of nutrient dumping, sedimentation and carbonate accretion. The study localities were chosen to cover a wide range of both environmental habitats and analytical micropaleontological procedures. These are Moorea (French Polynesia), and the nearshore habitats of the Gulf of Guinea in both Gabon and Nigeria.<br /> Foraminiferal assemblages from shallow-water nearshore and reefal environments around Moorea were investigated. They have large-scale spatial distribution patterns of habitat specific assemblages. Generally, diversity gradients increase from bay inlets to the reef barrier, but highest species richness is in fringing reefs, an area that represents a mosaic of habitats. The Foram Index indicates that the innermost bays and some outer bay fringing reef habitats are under direct natural and anthropogenic influences. In Moorea, a total of 364 foraminiferal species has been recorded. Images of representative species were taken by Scanning Electron Microscope (SEM) and arranged into 39 plates. Generally, this forms the basis of identification of benthic species from French Polynesia.<br /> The first survey of foraminifera from very shallow coastal sites in Gabonese waters revealed that the benthic foraminiferal communities display diverse assemblages of modern benthic foraminiferal representing a diversified and unique community structure. This suggests that the true diversity of shallow benthic foraminiferal species may be significantly higher. There are abundant symbiont-bearing taxa and a high species richness. This is an indication that the sampled sites are not yet strongly affected by drilling operations of the oil companies. Moreover, the composition and vertical zonation of modern benthic foraminifera was studied at two intertidal mangrove environments in the Akanda National Park, Gabon. Two faunal zones that are vertically constrained with regard to elevation were erected. Tides play a critical role in the species richness of individual assemblages. Their distribution shows a great potential for sea level reconstructions. The study constitutes the first survey of mangrove foraminifera from Gabon.<br /> Investigation of foraminifera, thecamoebians and diatoms within the Ologe Lagoon of southwestern Nigeria was performed. The benthic foraminifera show a low diversity with only four tolerant agglutinated species. Only three indicator species of thecamoebians were recorded along with two large benthic diatoms species. Their presence verifies the extent of freshwater invasion as well as the extent of activities that have impacted the habitat over time. The resulting patterns of distribution are interpreted to be a function of differential susceptibility and individual tolerance levels and highlight the potential of meiofauna studies as a tool for environmental monitoring.