الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 199 |  |  |
| | | from | 199 | | |
Abstract
Coral reefs are environmentally important marine ecosystems, as they support a tremendous diversity of plants and animals in the Sea. Coral reefs shield coastal areas from storm waves and allow other ecosystems to be formed by depositing and accumulating calcium carbonate rocks and sand. Coral reefs comprise more than 250 species of scleractinian corals, the Red Sea’s most important hermatypic (reef-building) organisms. Corals and their zooxanthellae and symbiotic algae form a mutualistic symbiosis, as both partners drive benefit and association; corals receive photosynthesis and a range of products, including sugars, amino acids, and large compounds such as small peptides and lipids products. In return, the dinoflagellate symbionts gain access to a rich supply of inorganic carbon, inorganic nitrogen, and phosphorus from the waste metabolism of the host.
Coral species are threatened world-wide by environmental changes, both from global pressures, particularly ocean warming and acidification, and local pressures such as terrestrial runoff, fishing and touristic activities, sedimentation, and oil pollution. Oil spill critically affect the health of the coral reef community on large scale as oil particles bioaccumulate in coral tissues and slow to depurate. The direct effects of oil spill vary in severity with the specific conditions, including oil type and quantity, species composition, time of exposure, and the nature of oil exposure. Oil pollution from both marine and land-based sources is a significant environmental stressor.
Oil pollutants in the marine environment may stimulate adverse effects on man and other organisms. Oil accumulates in the marine environment mostly due to the accidental or deliberate release of oil from ships, tankers, and damaged pipelines. Additionally, a significant amount of oil enters the seawater due to oil production and exportation activities. Shallow coral reefs are routinely subjected to multiple environmental pressures, including high ultraviolet radiation (UVR), high temperatures, low pH, and fluctuations in water quality parameters such as salinity, sedimentation, and nutrients. The symbioses between corals and various related microorganisms, including viruses, dinoflagellates, archaea, bacteria, and fungi that are necessary for host homeostasis may also be disturbed by oil.
Sedimentation limits coral distribution and is one of the most common causes of the degradation of coral reefs. In coral colonies, sedimentation stress increases linearly with the duration and amount of sedimentation. Coral growth rates decline with increasing exposure to sediments, symbionts are known to be expelled (bleaching), and tissue loss occurs. Sedimentation onto the colony surface is considered a stress to corals because sediment rejection leads to the down-regulation of photosynthesis and increased rates of respiration and mucous production. Photo-physiological stress occurs within hours of exposure to sedimentation and is strongly related to grain size, organic content and nutrient composition of the sediment. Reduced photosynthesis: respiration ratios have also been described in corals under elevated turbidity and may be due to increased respiration or reduced photosynthesis.
The present study aims to examine the effects of different anthropogenic stresses on coral health and survival by analyzing the physiological and ecological responses to crude oil and sedimentation stresses. Coral colonies of G. fascicularis, A. humilis, and P. lobate, were collected from the Red Sea, Gulf of Suez, El-Ain El-Sokhna. Corals samples had exposed to five concentrations of crude Oil (including 10.0, 1.0, 0.1, 0.01, and 0.001 mg/l) and four varied sizes of sediment (including very fine sand (<0.125mm), medium sand (0.5mm), coarse sand (1mm), and gravel (˃ 2mm)) for four days. Coral samples had investigated by SEM after being exposed to crude Oil. Zooxanthellae density and photosynthetic pigments (chlorophylls) have been measured after sediment exposure. pH, salinity, DO, and P/R ratio have been analyzed by statistical analysis to investigate coral species under these stressors.
The G. fascicularis and A. humilis showed high mortality after 48 hours of crude oil exposure to high concentrations (10 mg/l) of crude oil, but Galaxea fascicularis tolerated the first four concentrations for 72 hours. On the other hand, A. humilis suffered from total death for 1 and 10 mg/l concentration and 50% survivability for 0.1 mg/l, while all colonies death after 96 hours.
There are significant variations P/R ratio that happens after 72h is highly varied from 24h and 48h, which means that the P/R ratio tends to take time to show a significant variation (P< 0.05). There was a significant differentiation (P< 0.05) between both investigated species.
Images of the scanning electron microscope (SEM) displayed enormous amounts of crystals in the two species after 48 hours of exposure to crude Oil as a defense response to the impact of oil pollution; this indicated that G. fascicularis might deal with any stressors by producing many crystals as a defense mechanism. There are fungal, bacterial, and algae communities observed in treated and untreated colonies. Fungi were widely distributed in G. fascicularis polyp and affected by oil concentrations; fungi decrease with increasing oil concentrations. So, the responses of fungi in this coral species were according to oil spill concentration.
Many bacterial communities observed in G. fascicularis rather than A. humilis. While a small number of endolithic algae in two species only after 2 and 48 hours of exposure. Consequently, our results suggest that the Large Polyp Stony Coral (LPSC) G. fascicularis showed higher tolerance to oil pollution, while the Small Polyp Stony Coral (SPSC) A. humilis is more vulnerable to the impact of crude oil than G. fascicularis.
After exposure to sedimentation, the high sediment clearance in A. humilis than in P. lobata at very fine and coarse sand (<0.125mm and 1mm), while low sediment clearance at medium sand and gravel (0.50mm and ˃2mm). There was a significant differentiation (P ˂0.05) between the two species in which A. humilis could clear sediment than P. lobata. Acropora humilis has a higher density of zooxanthellae than P. lobata when exposed to sediment in which it is high at very fine sand (<0.125mm), while lower density at medium sand (0.50mm) treatment.
The absorbance of the chlorophylls was different between A. humilis and P. lobata, which is higher in A. humilis than in P. lobata. Chlorophylls and carotenoids have different values between the two investigated coral species according to sediment size compared to the control. Responses of two coral species to varied size of sediment in terms of chlorophyll absorbance differs from those sizes that are high peaks at <0.125mm and 0.5mm. Coral A. humilis and P. lobata have lower quantities of chlorophyll a in all varied sediment sizes. However, chlorophyll b and carotenoids have high amount according to sediment sizes and species.
Consequently, our findings indicate that branching polyp A. humilis retains little sediment and can be tolerant for a long time. Otherwise, the massive polyps (TPSC) P. lobata maintained a significant amount of sedimentation and could be tolerated briefly.