Ostracoda and Foraminifera as indicators of anthropogenic impacts – case studies from Sub-Saharan Africa

Rising sea levels and intensifying storms, as a consequence of a changing climate, impact our coastal ecosystems. This impact is exacerbated by human-induced pressures which include: organic and contaminant pollution by agricultural activities, industry, urban sewage, and traffic threatening ecosystems and its services, and increasing human populations.

Within the two studied regions of Ghana and South Africa there is a paucity of effective water quality monitoring data, management, and strategies. With the changing climate and rising water demands, it is critical to maintain and restore water bodies to ensure their sustainable future. To achieve this objective, one of the methods is to apply bioindicators. Today, there is a growing global interest in using bioindicators for water quality monitoring, which can provide valuable insights into environmental conditions by analyzing the abundance, and species and population composition of bioindicator populations. Bioindicators provide an integrated and sensitive approach to environmental monitoring by capturing the cumulative effects of contaminants over time, and by revealing indirect biotic effects and bioaccumulation that may be missed by traditional chemical and physical measurements.

We present the first comprehensive investigation of marginal marine Ostracoda and Foraminifera in Ghana, shedding light on their ecology and distribution in western Africa. Elevated Foraminiferal Abnormality Index (FAI) values correlate with high heavy metal concentrations and variable salinity, suggesting pollution-induced abnormalities. Certain taxa, such as Quinqueloculina sp., Ammonia sp., and Cyprideis remanei dominate in contaminated areas, due to their tolerance to various pollutants. This study reveals a positive correlation between organic matter content and faunal diversity, contrary to typical pollution-diversity trends, likely influenced by salinity and allochthonous inputs. Heavy metal concentrations exceed thresholds near settlements, indicating significant anthropogenic pollution. Despite the pollution, higher diversity is observed, particularly in sites with marine-like salinity, suggesting complex responses to mixed effects to salinity or hydrographical effects and heavy metals.

Furthermore, we conducted a study on the uMlalazi river, South Africa, where, despite previous assumptions regarding the river’s pristine condition, we found high pollution, emphasizing the need for a continuous monitoring strategy. For assessing pollution and ecological health, we focused on Foraminifera and Ostracoda. We identified 17 ostracod species and 19 foraminifer species. Three distinct assemblages correlated with varying salinity and Pollution Load Index (PLI) levels. Our findings support the common trend of reduced species diversity with increased pollution. FAI correlated with PLI, showing that malformations where predominantly anthropogenically driven. Geochemical analysis indicated significant anthropogenic pressure, with elevated concentrations of heavy metals, sulphur, and microplastics from human induced activities such as sugarcane farming, urban sewages, fish farming and unknown sources.

Our studies emphasize the potential of Ostracoda and Foraminifera as indicators of environmental pressure and stresses, and a call for a more complete datasets to establish clearer correlations between meiofaunal associations and pollution effects.