Environmental conditions of shallow waters alongside the southern Corniche of Jeddah based on benthic foraminifera, physico-chemical parameters and heavy metals

Abstract

The coastal environment along the southern Corniche of Jeddah is under increasing influence of human activities, including a semi-treated sewage outfall from many industrial factories. In early 2009, we evaluated the environmental status of this area. We measured water temperature, salinity, pH and dissolved oxygen; described substrates; and evaluated sediment samples for texture, heavy metals (Fe, Mn, Cu, Pb, Cr, Zn, Ni and Co) and benthic foraminiferal assemblages. We used cluster and canonical correspondence analyses to subdivide the study area into three facies: 1) The reef flat and lagoonal area is dominated by a Coscinospira hemprichii-Peneroplis planatus-Quinqueloculina seminula assemblage occurring in very shallow (≤3 m), warm (∼29°C), high salinity (40) waters, with a Quinqueloculina cf. Q. limbata-Q. laevigata-Ammonia tepida assemblage co-occurring where sediments are muddy and enriched in organic matter and heavy metals. 2) The forereef area is dominated by an Amphistegina lessonii-Assilina ammonoides assemblage occurring in well-oxygenated (6-8 mg/1), deeper waters (10-65 m), with moderate salinity (∼38), temperature ∼27°C, and coarse sediments. 3) A Neorotalia calcar assemblage dominates the fringing-reef area where filamentous green algae proliferate on nutrients from the sewage outfall. Frequent occurrence of deformed tests and stress-tolerant species such as Ammonia tepida and Q. seminula, with a few photosymbiotic species, indicate the influence of pollution in the inshore area. On the other hand, the fore-reef area is characterized by clear, oligotrophic waters essential for endosymbiont photosynthesis of the Amphistegina lessonii-Assilina ammonoides assemblage. This study further documents the utility of benthic foraminifera in monitoring coastal environments, and adds the perspective of the influence of nutrient pollution under hypersaline conditions.