الفهرس 
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Abstract
AbstractThe bimonthly variation in environmental conditions and its impact on the composition and abundance of phytoplankton species were investigated in Chapter 1 of the present study. The investigation was caried out at 8 fixed stations in the Eastern Harbor (EH) of Alexandria, Egypt during June 2018 to April 2019. Insignificant variation in the range of physicochemical parameters was observed including, water temperature (19.38-30.98°C), pH value (7.89-8.73), salinity level (36.36-39.50‰), DO concentration (3.61-5.97 ml O2 L-1), and OOM concentration (1.05-5.05 mg O2 L-1). The nutrient salts showed a wide difference range including, ammonia concentrations (0.41-11.87 μM L-1), nitrate (0.13 - 13.26 μM L-1), nitrite (0.215-1.21 μM L-1), reactive phosphate (0.5-1.12 μM L-1), and silicate (0.39 - 8.82 μM L-1). The high values of N/P ratio recorded during the study period indicated that phosphorus was a limiting factor in the nutrient cycling and the key element controlling primary production in the EH. A total of 148 phytoplankton species and 93 genera were identified during the investigated period. Diatoms were the most dominant species and accounted for 44.28% of the total detected phytoplankton, followed by raphidophyte species (25.06%) and dinoflagellate species (24.82%). Phytoplankton standing crop attained an annual average value of 872.4 x 103 units L-1, and biomass (as Chlorophyll a indices) of 1.65 μg L-1. Diatoms, raphidophytes and dinoflagellates revealed important roles in phytoplankton diversity during the study period with the persistent occurrence of several toxic species in high counts such as the diatoms Skeletonema costatum and Thalassiosira gravida, the raphidophytes Chattonella marina and Heterosigma akashiwo, and the dinoflagellates Alexandrium minutum, Prorocentrum sp., Heterocapsa circularisquama and Gyrodenium fusiforme. These species were responsible for the massive phytoplankton red tide blooms appeared in the EH during summer months of June, August 2018, and April 2019. A correlation coefficient of biological factors with environmental conditions was assessed and discussed. Further, the principal component analysis (PCA) and cluster analysis (CA) were used to analyze the seawater quality data. According to these analyses, the EH area is still suffering from chronic eutrophication conditions all-round the year. This was indicated by the high detected concentration of nutrients and intensive phytoplankton blooms dominated by toxic species. Microplastics (MPs) contamination has become a global concern with potential impacts on the marine environment. Chapter 2 of the present study investigated the MPs pollution levels in the Eastern Harbor of Alexandria City along Mediterranean Coast of Egypt for the first time. Enhanced visual counting technique coupled with combustion analysis and differential scanning calorimetry (DSC) was applied to assess MPs abundance, composition, types, and potential sources in samples of seawater, fish digestive tracts, and sediments. This was the first study in Egypt to quantify MPs and provide a simple and economic method for MPs assessment. The results showed that the MP fragments extracted from the seawater, fish digestive tracts and sediments had various types, colors, sizes, and physical shapes, which suggesting different sources. An average number of 1283.5 ± 173.9 MPs particle L-1 were detected in the seawater during summer and winter seasons. A total value of 1621 particle kg-1 dry sediment of MPs were recorded in the sediment samples. The average MPs densities was significantly higher in Siganus rivulatus, Diplodus sargus, and Sardinella aurita fish species of 7527, 3593 and 1450 MPs fish-1, respectively than the other species. Thermogravimetric analysis (TGA) using combustion technique indicated an average weight of 2.095 ± 0.058 μg L-1 of MPs recovered from the seawater samples during the two seasons. S. rivulatus and D. sargus, recorded the highest MPs weights of 302 and 62 mg MPs kg-1, respectively than the other fish species. Furthermore, the total weight of MPs extracted from the sediment samples was 8.12 mg kg-1 dry sediment. The differential scanning calorimetry (DSC) identified 10 semi-crystalline polymers in the studied samples. Low-Low density polyethylene (LLDPE), polyethylene vinyl acetate (PEVA) and polypropylene (PP) were the most dominant MPs polymers. The dominance of glossy fragments, transparent filaments, colored fragments, and foam fragment in the EH water suggested secondary MPs originating from the fragmentation of larger plastic items of sea-based sources (such as antifouling paints, maintenance of ships, fishing gears and recreational activities). In addition, land-based sources including, single-use plastic bags and detergents contributed to plastic litter pollution in the EH. Chapter 3 of the study examined the responses of the marine diatom Chaetoceros muellerii to LDPE-MPs exposure with different particle sizes and concentrations. The addition of LDPE-MPs in the culture medium showed a significant inhibitory effect on the growth and physiological activities of C. muellerii during the growth period. Significant reduction in the photosynthetic pigment, protein, and carbohydrate contents of C. muellerii cultures was recorded. The maximum inhibition percentage was recorded for C. muellerii cultures treated with LDPE-MPs of 100 mg L-1 dose and 100μm particle size after 6 days of exposure, suggesting that the toxic effects of LDPE-MPs treatment on C. muellerii cultures were dependent on its concentration, particle size, and exposure time. On the contrary, a significant promoting effect of LDPE-MPs addition on the lipid content, CAT, and SOD antioxidant activities of C. muellerii was obtained. Furthermore, SEM images was used to observe the behaviors and interactions between C. muellerii cells and LDPE-MPs. It was clearly observed that LDPE-MPs was adsorbed on the surface of C. muellerii cells forming hetero-aggregate clusters. SEM results were in agreement with those of the growth and biochemical compound results, which showed that the physiological activities of C. muellerii was impaired by LDPE-MPs exposure. FTIR analysis showed that the exposure of C. muellerii cells to LDPE-MPs could reduce the quality of the biomass by changing the content of the organic functional groups of the protein and polysaccharide compounds. The DSC and combustion techniques was applied for quantifying and monitoring the hetero-aggregates between LDPE-MPs and C. muellerii cells. According to our knowledge, this is the first work to apply this technique for quantifying the LDPE-MPs accumulated on the algal cell surface.