الفهرس 
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Abstract
Coastal marine ecosystems provide various beneficial services such as nutrient cycling, detoxification of pollutants, food production, raw materials and habitats, regulation of storm-induced disturbances, as well as recreational and entertainment activities. Anthropogenic activities, climate change and extreme actions have led to severe environmental degradation in the coastal zone. Macrobenthos play an important role in aquatic ecosystems, they are widely used as indicators to assess environmental stressors in marine ecosystems.
The Egyptian Red Sea coast receives a variety of stresses due to over exploitation and has become very vulnerable to human related activities. The main environmental problems and threats to the Red Sea ecosystems include recreation and tourism activities, urban agglomeration, oil pollution, marine shipping, solid waste disposal, activities of phosphate industry and shipment and fishing activities.
Therefore, the present work aimed to study the impact of seasonal changes of some environmental factors and anthropogenic effects on macrobenthic communities of the Red
Sea coast of Egypt as one of biomonitoring organisms in coastal ecosystems. As well as investigate the spatial and seasonal impacts on some heavy metal accumulations and gonad maturation and biochemical responses of two different macrobenthos; Tridacna squamosa (Bivalvia) and Echinometra
mathaei (Echinoidea) inhabiting three different sites at the Red Sea Coast of Egypt.
The present work aims to carry out the following points:
1. Study the community structure of macrobenthos in the Red Sea coast of Egypt as one of biomonitoring organisms in coastal ecosystems.
2. Seasonal determination of ecological factors and heavy metals, which may have influence on Macrobenthos populations.
3. Evaluate inter and intraspecific variations in heavy metals accumulation in some selected bioindicator macrobenthos.
4. Investigate the spatial and seasonal impacts on biochemical responses of two bioindicator macrobenthos; Tridacna squamosa (Bivalvia) and Echinometra mathaei (Echinoidea) inhabiting the Red Sea cost of Egypt.
5. Study the effect of environmental conditions on the reproductive state and gonadal development of both selected bioindicator animals.
To achieve these aims, two trips to the field were done to investigate the benthos communities and collect Echinometra mathaei and Tridacna squamosa. Three sites along the Red Sea cost were selected to perform this study; El-Hamrawen, Sedy
Malek and Porto Ghalb. In July 2019, animal samples were collected from El-Hamrawen and Sedy Malek while in January
2020 samples were collected from the investigated three sites.
The collected animal sample groups coded by Hs, Ms, Hw, Mw and PW refer to samples from El-Hamrawen during summer, Sedy Malek during summer, El-Hamrawen during winter, Sedy Malek during winter and Porto Ghalb during winter, respectively.
Macro-benthic fauna were observed and recorded by snorkeling and scuba diving in the depth reach to 5m at the investigated sites. Two lines transect were extended in littoral zone, for each one macrobenthos were recorded within (5m×5m) quadrate on either side of the line transect every 10m alternatively. During sampling, environmental variables; air and water temperatures (ºC), water hydrogen ion concentration
(pH), salinity (ppt), dissolved oxygen (mgL-1) and conductivity (ms.cm-1) were measured using Hydrolab. Sediment samples (about 1kg/sample) were collected from investigated sites and dried in direct sunlight after removing existing Biota (fauna and flora) and preserved for carbonate and organic matter contents analyses. In the laboratory, total organic matter (TOC), carbonate contents, and sediment grain size analyses were estimated.
For each sample group 10 specimens from each animal
(Tridacna squamosa and Echinometra mathaei) were weighted and dissected and their gonads were weighted and preserved in ice until they preserved in -20 °C until heavy metal and biochemical analyses. Samples from the gonads were preserved in formalin 10% and labeled to keep them in their normal structure until reached the laboratory for sectioning and histological analysis.