Sedimentation threats to Red Sea corals : an ecological study of reefs in the Hurghada Region, Egypt

Selim, Abdalla Eliwa Mohamed

Abstract

Hurghada coastal reefs have encountered a huge modification in the last three decades, associated with an increase in sediment input from coastal development. The aim of this study was to examine the impact of sediment on reef health at a number of sites along the coast of Hurghada encountering differing sedimentation loads. A range of physicochemical parameters were measured in the field and related to a variety of reef health indicators. This was supported by laboratory based experiments examining the direct impact of sediment on coral bleaching and mucus production.

Annual and seasonal patterns of sedimentation were investigated along the Hurghada coastal area of the Red Sea using sediment traps. Suspended particulate matter (SPM) and the percentage of non-carbonate sediment in bottom sediment were sampled. Physicochemical parameters measured in the field included temperature, salinity, depth, pH, specific conductivity SPC, dissolved oxygen DO, total dissolved salts TDS, percentage of dissolved oxygen DO% and turbidity using a multprobe. Inorganic phosphates, silicate, ammonia, nitrite and nitrate concentrations were determined.

Reefs were surveyed to determine a number of reef health indicators including coral cover, percentage of live and dead coral, new recruits, abundance, species richness, the percentage of r-strategist, Diversity Index, Deterioration Index (DI) and disturbance. Three species of Acropora were transplanted in this study and their survival was investigated. Six fish families were surveyed using belt transects to examine changes in community structure.

Zooxanthellae density was measured in transplanted corals in field and laboratory conditions to determine the effect of sedimentation on coral bleaching. In addition, direct feeding experiments were performed using fluorescein-isothiocyanate sediment to assess coral ability to cope with higher sedimentation. Mucous secretion by corals was measured in field and laboratory to test variations under different sedimentation condition.

Significant differences between sites in sedimentation rate, SPM and the percentage of non-carbonate sediment were observed. Sedimentation and SPM were also shown to reduce coral cover, species richness, diversity, mean colony size of branched corals and the abundance of algal feeding fish. Other parameters such as non-carbonate sediment, turbidity and percentage of mud in bottom sediment affected corals and fish to various degrees.

Sedimentation did not appear to reduce the number of live or dead corals or new recruits. In addition, it did not affect the distribution of r-strategist as a pioneer group of corals. It did not affect transplant survival or macroborer distribution, although it did reduce zooxanthellae density and increase mucus secretion and sediment uptake by Lobophyllia hemprichii. Coral abundance, mean colony size of massive corals and coral feeder abundance were not reduced under the observed sedimentation conditions. The Deterioration Index did not provide a strong tool to gauge coral condition in this study.

Although many indicators did not show significant correlations with sedimentation, SPM, turbidity or non carbonate sediment, it was found that sites with the highest readings of these parameters has the lowest biological quality. These finding support early studies that showed that low sedimentation levels do not have significant impact on coral health. Some sites showed continuous degradation and increased level of sedimentation from land sources and need urgent mitigation measures to be followed by coral restoration and transplantation.

Citation

Selim, A. E. M. Sedimentation threats to Red Sea corals : an ecological study of reefs in the Hurghada Region, Egypt. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/4209440

• Thesis Type: Thesis
• Deposit Date: Aug 15, 2011
• Publicly Available Date: Feb 22, 2023
• Keywords: Biological sciences
• Public URL: https://hull-repository.worktribe.com/output/4209440
• Additional Information: Department of Biological Sciences, University of Hull
• Award Date: Jun 1, 2007