Hypersaline benthic foraminifera from the Shuaiba Lagoon, eastern Red Sea, Saudi Arabia: Their environmental controls and usefulness in sea-level reconstruction

The Shuaiba Lagoon is a fossil back-reef, hypersaline small basin located 80 km south of Jeddah city on the eastern Red Sea coast, Saudi Arabia. The surface sediments of the lagoon were investigated for their benthic foraminiferal content in order to correlate, in general, with environmental factors such as temperature, salinity, pH, sediment grain size, organic matter and, in particular, with tidal elevations to develop a training set for predicting sea-level changes in the lagoon. Hierarchical cluster analysis divided the benthic foraminifera in the Shuaiba Lagoon into four distinct faunal assemblages. Quinqueloculina cf. Q. limbata (Assemblage 1) and Monalysidium acicularis (Assemblage 2) assemblages dominated the intertidal–high subtidal areas (0.3 to − 0.5 m, LAT). The Peneroplis planatus–Sorites orbiculus Assemblage 3 occurred abundantly at all subtidal elevations (0 to − 1 m, LAT), whereas the Quinqueloculina costata–Spiroloculina communis–Elphidium striatopunctatum Assemblage 4 dominated the lowest elevations (< − 1.5 m, LAT) in the lagoon. Canonical correspondence analysis indicated that the intertidal–high subtidal assemblages were positively correlated with tidal elevations in the Shuaiba Lagoon, consequently, their training set yielded a model predicting sea-level changes with a precision of ± 0.16 m, but when they were incorporated with the lowest-elevation (low subtidal and below subtidal) assemblages, a wide error (± 0.33 m) was produced. Abundance distributions of all assemblages were also affected by the other environmental factors such as salinity, organic matter and temperature, but pH was an important controlling factor on many assemblages due, likely, to high algal photosynthesis in algal-dense substrates. The effect of these factors on the predictability of the intertidal–high subtidal training set is unavoidable and it could be compromised by making a model from the different niches of the intertidal–high subtidal area.