الفهرس 
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Abstract
The present work aimed to evaluate the spatial and seasonal variations in nutritional composition, antioxidant and antimicrobial activities of some seaweed species of the Red Sea. To select the algae that could be used as a sustainable resource, macroalgal assemblages were seasonally surveyed during the year 2017 in three sites which represent different hydrographic parameters along the northwestern coast of the Red Sea. Data was collected on species composition, cover, and biomass as well as on the environmental parameters.
Environmental parameters
1. Physical conditions:
Variations in water temperature were strictly related to seasonal changes with a minimum in mid of winter (17.6 oC) and maximum in mid of summer (32.1 oC), with no significant difference between sites.
The degree of turbidity was highly significant varied among seasons; it was at a maximum average (6.2 NTU) during autumn at site II, while the minimum average was recorded during summer (2.3 NTU) at site III; variation related to suspension of organic matter by water movement.
Sedimentation rate was varied between sites and seasons. The lowest value of 0.0005 gm. cm-2. Day-1 was found at site III during summer while the highest value of 0.020 gm. cm-2. Day-1 was recorded at site II during autumn.
2. Chemical parameters
The pH value was varied between seasons and sites. It was found on the alkaline side with a maximum of 8.80 at St. II, and a minimum of 7.80 at St. III. It related to the balance between organic decomposition and buffering by carbonates and bicarbonates.
Sarah H. Rashedy, 2019. Spatial and Temporal Variations in Nutritional Composition, Antioxidant
and Antimicrobial Activities of Some Seaweeds from Red Sea, Egypt……………….. PhD Thesis
198
Salinity values showed minor fluctuations between 43.2 ppt in the mid of summer and 41.04 ppt in mid of autumn, with significant differences related to the influence of both the evaporation and local current convey.
The general distribution of DO revealed high values and presence of well-oxygenated waters in the studied area, It ranged from 4.8 mg. l-1 at site II in spring to 7.4 mg.l-1 at site I in winter.
The nutrient salts, inorganic phosphorus and nitrogen as well as reactive silicate were examined in the three sites. Nitrite was highly significant varied between sites and seasons. The maximum nitrite concentration (0.14 μM) was recorded during winter while the minimum values were recorded at spring season (0.03 μM).
Dissolved nitrate was highly significant varied among sites and seasons. The higher median of nitrate was recorded during winter (1.52 μM). While the lowest median was recorded in autumn (0.28 μM).
Dissolved ammonium was highly significant varied among sites and seasons. The maximum values were recorded in summer and autumn (3.83, 3.62 μM respectively), while minimum values were occurred in spring (0.29 μM).
Dissolved inorganic phosphate of seawater has fluctuated among the surveyed sits and seasons. Site I had the highest value of phosphate (0.22 μM) during winter compare to other sites, which may be due to the effect of low sewage effluents and the land filing at this site. While the lowest values have occurred at site III (0.04 μM) during summer.
The reactive silicate displayed a highly significant difference between the selected sites and seasons. The highest concentration of 2.04 μM was recorded in summer at St. I, and the lowest of 0.44 μM in winter at the same site. SiO4 displayed a large variability due to the supply of
Sarah H. Rashedy, 2019. Spatial and Temporal Variations in Nutritional Composition, Antioxidant
and Antimicrobial Activities of Some Seaweeds from Red Sea, Egypt……………….. PhD Thesis
199
SiO4, which flows in the Red Sea through the strait of Bab El-Mandab, biological consumption, organic matter decomposition and the partial dissolution of quartz particle transported to the sea from the surrounding desert during sandstorms.
Taxonomic diversity and algal coverage
1. Thirty-six species of macroalgae were collected from the studied sites. About 36.1% of these species (13 species) belongs to phylum Chlorophyta, 36.1% (13 species) belongs to phylum Phaeophyta and 27.8 % (10 species) belongs to phylum Rhodophyta.
2. from all recorded species in this study, six species were dominant and had the highest coverage during the year of survey. Also, they were found at three sites and four seasons. Thus, they were selected to study the spatial and temporal variations of their nutritional composition, antioxidant and antimicrobial activities. These species are Caulerpa racemosa var. gracilis from Chlorophyta, Padina boergesenii, Polycladia myrica, Hormophysa cuneiformis and Sargassum aquifolium from Phaeophyta and Digenea simplex from Rhodophyta.
Ecological studies on the selected seaweeds.
During survey, Sargassum aquifolium was found at three sites and four seasons. It had the highest average of cover (43%) with biomass of 421 gm. m2 of fresh wt. at site III in autumn, while the lowest average cover (5%) of it was recorded at site II and I with biomass average of 49 gm. m2 of fresh wt. in winter and spring, respectively.
Padina boergesenii also was found at all sites and all seasons except winter. It had a cover average of 35 % with biomass of 279 gm. m2 of fresh wt. at NIOF (site I) in spring. While the lowest cover average (1 %) of it was recorded at site I and III with biomass average of 4 gm. m2 of fresh wt. in winter.
Sarah