Recent brackish water Foraminifera and Ostracoda from two estuaries in Ghana, and their potential as (palaeo)environmental indicators

Abstract

To improve the indicator value of marginal marine Foraminifera and Ostracoda of Ghana, we analysed 22 surface sediment samples for microfauna. They were obtained from the Keta Lagoon and Densu Estuary covering a salinity range from marine waters to 17.5 and one sample within the hyperhaline range (70). Except one, all samples contain Ostracoda and Foraminifera. There are 34 ostracod species belonging to 24 genera. Dominating is Cyprideis remanei Klie, 1940, other abundant species are Pseudoconcha sp., Pseudoconcha hartmanni Omatsola, 1970, Loxoconcha lacunensis Omatsola, 1970 and Chrysocythere foveostriata Brady, 1870. We found 28 Foraminifera species belonging to 22 genera with the dominant taxa Ammonia sp. and Quinqueloculina spp. There are five associations, which are mainly driven by the hydrological regime and organic pollution. In contrast to a usual diversity trend reflecting high levels of pollution by lower diversity, our results show higher diversity associated with sites of higher pollution levels. The most tolerant (salinity and pollution) ostracod taxon is Cyprideis remanei, which is occurring over the whole salinity range documented as well as in contaminated areas with very high LOI and heavy metal concentrations. In the investigated samples we found many deformed Foraminifera with anomalies like multiple tests, changes in coiling and aberrant shapes of the chambers. Ongoing investigations in estuaries of Ghana are expanding our data set and will provide a better understanding of species-specific reactions of Ostracoda and Foraminifera to anthropogenic pressure.