Calcium Composition and Microstructure of Coral <i>Stylophora pistillata</i> under Phosphate Pollution Stress in the Gulf of Aqaba

Abstract

Corals and coral-reef ecosystems have been known to be extremely sensitive to environmental pollution, which effects on growth and calcification of their skeletons. Diffused phosphate dust during loading and shipment in seawater was found to cause serious impacts on corals by inhibiting calcification in their skeletons. Calcium concentrations in cultured fragments of coral Stylophora pistillata from Phosphate Terminal (PT) site in the Jordanian Gulf of Aqaba were investigated and compared with fragments from the same colony cultured in the Marine Science Station (MSS) site as marine protected area. Energy Disperse X-rays (EDX) spectroscopy and Scanning Electron Microscopy (SEM) were employed to determine the elemental composition of coral fragments and identify their microstructural characteristics, respectively. EDX results showed that coral samples from the Phosphate Terminal (PT) site were poorly mineralized with significantly low concentrations of calcium which were only about 12% of those from the MSS control site. Moreover, higher amounts of O and C in the elemental analysis of corals from the PT site indicated domination of organic matrix content in their skeleton which is typical for corals under phosphate pollution stress. This result was in accordance with the SEM images of the PT samples which exhibited alteration in their microstructure morphology resembling organic matrix as a major constituent, unlike the SEM images from the MSS protected area. These results strongly suggest that phosphate dust which is diffused during exportation through loading and shipping in the Gulf of Aqaba has adverse impacts on corals and marine ecosystem through decreasing calcium mineralization in their skeletons.

Heterogeneous Microstructure and Distribution of Trace Elements in Coral <i>Stylophora pistillata</i> Nursed in the Phosphate Loading Berth Site in the Gulf of Aqaba

“…In Figure 2, the dark regions resemble the less-Ca phases and the bright ones indicates for the mineralized areas. This heterogeneous structure comes in accordance to the last study by Al-Sawalmih [27] on Stylophora pistillata coral samples from the phosphate pollution site, reporting dominance of organic/low-mineralized microstructure in SEM images and elemental analysis. This can be attributed to the role of phosphate in enhancement of coral zooxanthellae photosynthesis that is responsible for synthesis of organic matrix in the skeleton [31].…”

“…In all locations, Ca concentrations were very low as expected and recorded in previous study on such coral in the same site [27] which was only 2.56 wt%, which is around 12% of the average in the control sample (21.95 wt%) but with a focus area Table 1. Concentrations in wt% of C, O, Ca, and trace elements in the EDX scanned positions 1-4 in the coral cross section BSE image ( Figure 2).…”

“…It was found that phosphate is responsible for increasing the death rate of Stylophora pistillata coral [25] while other study reported tolerance of coral species Stylophora pistillata to phosphate [26]. Al-Sawalmih [27] in his studies on branches Stylophora pistillata that are nursed in the Phosphate Loading Berth (PLB) site, found very low calcium composition in the aragonitic skeleton, about 10% of it in the control samples. He also found that these microstructures of these branches suffered from alteration due to dominance of organic fibers in the skeleton.…”