الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 233 |  |  |
| | | from | 233 | | |
Abstract
The effects of different human activities on conl reefs were investigated at seven selected locations along the northern Red Sea of Egypt. Reef surveys indicated that all observed coral damage (coral death, coral breakage, algal overgrowth and coral diseases) was most frequent within the upper ten meters depth. The anthropogenic disturbance of various sorts was the main cause of reef damage because severe oceanographic and climatic changes are extremely rare in the area of study. Sixteen physico-chemical variables were assessed in the present study. Mean water temperature ranged from 23.89 ± 2.31 °C at location IV to 26.27 ± 2.45 °C at location VII, while mean salinity was flactuated between 39.64 ± 0.2 960s at location VII and 42.65 ± 0.17 96os at location I. Thus, salinity increases towards the north. The maximum mean concentration of dissolved oxygen 6.53 f 0.17 mg 02 was recorded at location VII, whereas the minimum mean 5.14 ± 0.19 mg 02 14-1 was recorded at location II. Values of pH showed no obvious variation among the sampled locations.
The common indicators of eutrophication in the studied sites are increased nutrient and phytoplankton (as indicated by chlorophyll a) concentrations in the water column. The highest mean concentration of chlorophyll a (0.28 ± 0.02 lig I)) occurred at location III, whilst the lowest value was observed at locations VI and VII (0.14 ± 0.07 and 0.14
0.04 ttg I), respectively). Nutrient concentrations showed relatively similar trend, whereas the mean concentrations of total dissolved inorganic nitrogen (nitrite + nitrate + ammonia) and dissolved phosphate were highest at location III (5.02 ± 0.95 and 0.42 ± 0.1 pM, respectively) and lowest at location V (2.07 ± 0.37 and 0.06 ± 0.02 pM, respectively). Enhanced sewage discharge, seepage of wastewater and terrestrial sediment input seems to be the main causes of enhanced nutrient concentrations at location III (Marine Biological Station). Impacts of eutrophication on coral reefs are increased dominance of macroalgae which compete with corals for substrate space and overgrow living coral tissue, and increased concentration of total suspended particulate matter
in the water column.
Concentration of total suspended particulate matter (SPM) was significantly different among the investigated reef sites. Site I (El-Ain Al-Sukhna) showed the highest mean concentration of SPM (12.52 ± 1.18 mg L-1), while the lowest value (5.52 0.31 mg 1,-1) was reported at site V (Shag) Abu-Galawa). Elevated concentration of SPM affecting reef corals directly by physical smothering or indirectly through a reduction of light levels available for zooxanthellae photosynthesis. The probable causes of high levels of SPM in the area of El-Ain Al-Sukhna are enhanced terrestrial sedimentation and resuspension of bottom sediments due to human trampling on reef flats.
Sedimentation rate exhibited high significant difference among the investigated reef sites. Maximum mean of sedimentation rate 317.76 ± 73.73 mg cm-2 day”’ was found at site II (Ras Za’farana), while the minimum mean 3.71 ± 0.67 mg cm-2 day-1 was found at site IV (Sha’b Saad). Excessive sedimentation can adversely affect the structure and function of the coral reef ecosystem by altering both physical and biological processes. Heavy sedimentation was associated with a significant reduction of live hard coral cover, hard coral density, species richness, species diversity, evenness index and population density of zooxanthellae, and increased coral mortality and coral diseases. It is suggested that landfilling concomitant with building activities, beach enhancements and land reclamation were the most significant anthropogenic factors responsible for increased terrestrial sedimentation at the northwestern Gulf of Suez (locations I and II).
Total carbonate and organic matter (TOM) contents in reef sediments were significantly varied among the studied locations. Location V showed the maximum mean percentage of total carbonates (90.66 ± 1.85%), while location II showed the minimum value (42.44 ± 1.92%). Increased sedimentation rate is significantly correlated with decreased carbonate content in reef sediments. This would probably because the enhanced terrestrial sediment accumulation which are poor in carbonate content significantly reduce the net production of total carbonates by corals. The highest mean percentage of TOM 12.15 ± 1.29% was determined at location I, whereas the lowest value 2.94 ± 0.82% was determined at location V. The significant positive relationship between increased TOM content and enhanced trace metal concentrations in reef sediments demonstrated that organic matter is a significant concentrator of these metals. Generally, increasing TOM content in reef sediments was accompanied with increasing trace metal concentrations, which is adversely affected on coral population.
The mean concentration of total dissolved and dispersed petroleum hydrocarbons (DDPH) in seawater ranged between 7.24 ± 1.14 lig at location IV and 34.83 ± 26.57 jig L-1 at location II. Concentration of total petroleum hydrocarbons in reef sediments (TPH) showed significant variation among the sampled locations, where the highest mean concentration (52.85 ± 8.33 lig g-l) was measured at location II and the lowest value (1.40 ± 0.01 lig g-l) was measured at location V. The higher levels of petroleum hydrocarbons reported at locations II and I were probably attributed to the massive oil spillage associated with the different petroleum activities in the Gulf of Suez. On the other hand, the lower concentrations of petroleum hydrocarbons in the area of Hurghada (locations III, IV, V and VI) may be attributed to the fact that this area is protected from the prevailing southerly currents which presumably carry the oil with it, by projected head lands and cluster of islands. The increasing oil concentration was significantly accompanied with decreasing live hard coral cover, hard coral density, species richness, species diversity, evenness index and zooxanthellae density, and increasing dead coral cover.