Factors influencing foraminiferal assemblages in coastal sediments of the Cross River Estuary, Southeast Nigeria, Gulf of Guinea

Abstract

Estuaries are crucial coastal ecosystems facing increased pressures from human activities. The Cross River Estuary in Nigeria is a vital tropical mesotidal estuary influenced by diverse anthropogenic and natural processes. This study investigated the distribution of foraminiferal assemblages in the estuary's sediments, alongside environmental parameters such as heavy metals, pH, depth, temperature, salinity, mean grain size, and dissolved oxygen. Field sampling involved collecting 55 bottom water and sediment samples, with laboratory analyses focusing on grain-size distribution, foraminiferal identification, and heavy metal concentrations. Results indicated that heavy metal concentrations, except for iron, were within permissible limits. A total of 287 benthic foraminiferal tests representing four species were identified. These were primarily agglutinated species, with Arenoparrella mexicana and Miliammina fusca being the most abundant. Foraminiferal distribution was influenced by sediment type, salinity, and pH, rather than heavy metal concentration. Principal Component Analysis (PCA) revealed weak relationships between foraminiferal species and environmental variables, indicating limited influence of mean grain size and heavy metals on foraminiferal distribution. The study highlights the adaptability of certain foraminiferal species to a wide range of environmental conditions and underscores the need for continuous monitoring of the estuarine ecosystem to assess the impacts of ongoing anthropogenic activities. The findings provide a baseline for future environmental assessments and the use of foraminifera as bioindicators in tropical estuarine environments.