Factors Influencing Foraminiferal Assemblages in Coastal Sediments of the Cross River Estuary, Southeast Nigeria, Gulf of Guinea

The Cross River estuary in Nigeria, a tropical meso-tidal estuary, empties into the Atlantic Ocean through the Gulf of Guinea. With a major navigation channel for maritime transportation, the estuary also provides commercial fishing, sand mining, and seafood trading. Sediment samples were collected at water depths of 1–12 m. From 55 samples collected, benthic foraminiferal specimens were found in only 12, representing three agglutinated species (Arenoparrella mexicana, Miliammina fusca, and Arenoparrella sp.) and one calcareous hyaline species (Ammonia sp.). Cluster analyses revealed two distinct sample clusters, one with two subgroups. Group 1a, four samples from < 10.4 m depth, were fine-grained sands containing Arenoparrella mexicana and Ammonia sp. Bottom waters were brackish, with low pH and high concentrations of dissolved oxygen (< 11 mg/l). Group 1b (4 samples), from muddy to very fine-grained sediments from shallow (< 2 m), brackish water with low pH and low dissolved oxygen, included all four species. The Group 2 assemblage, dominated by Arenoparrella mexicana, was also found in muddy to very fine-grained sediment at ≤ 5.5 m, in brackish waters with variable pH and low dissolved oxygen (< 2.5 mg/l). Arenoparrella mexicana was the most widely distributed species, while M. fusca was limited to organic-rich muddy sediments. Foraminiferal distributions correlated with environmental parameters including salinity, pH, and heavy metal concentrations. The study underscores the impact of anthropogenic activities on estuarine ecosystems, resulting in low foraminiferal density and diversity. These findings contribute valuable insights for monitoring environmental changes in the Cross River Estuary.