Spatial and vertical variability of summer coccolithophores in relation to water column stratification and nutrient gradients in the Gulf of Aqaba

Coccolithophore abundance and diversity were examined across five stations and depths in the Gulf of Aqaba during late summer (18–24 September 2016). Temperature varied mainly with depth, nutrients were largely uniform except nitrate and chlorophyll- a showed little spatial variation. Abundance peaked at the deep chlorophyll maximum, averaging 38.4 ± 20.2 cells ml −1 , with Gephyrocapsa huxleyi dominating and Umbellosphaera tenuis as a key contributor constituting 40.2% and 8.5% of the total density, respectively. A total of 64 species (36 genera) were identified, including eight new Red Sea records, with Syracosphaeraceae as the most diverse family (23 species). Clear vertical zonation patterns were observed, with four species— G. huxleyi , Syracosphaera pulchra , U. irregularis and U. tenuis —occurring ubiquitously across depths and stations. Coccolithophore density showed significant correlations with ammonia (positive) and salinity (negative) highlight strong environmental control of coccolithophore communities in these oligotrophic waters. In general, the results indicate the high diversity, vertical zonation and environmental interaction of coccolithophore community in the oligotrophic waters of the study area.