This study was undertaken to investigate the ecophysiological response of ‎Avicennia ‎marina to the fluctuating conditions along the Red Sea shoreline over the year 2017/2018. Parallel ‎changes in ambient sea water characteristics over the same ‎experimental period were determined. ‎Three visits to the experimental localities were ‎paid on three prescheduled intervals corresponding ‎to spring (April), summer (August) and winter (December) ‎seasons to study sites namely ’Al Birk’ ‎‎(B: 18° 11’ 36’’ N, ‎‎41° 32’ 50’’ E) and ’Huraydhah’ (H: 17‎‏°‏‎ ‎‏4‏‎8’ ‎‏29‏‎’’ N, 41° 51’ 57’’ E).‎ The ‎dwarfing and the sparseness of the A. marina forests along the Red Sea shoreline were mainly due ‎to the harsh environmental conditions. Namely, the high and the large fluctuation of temperature, ‎the low precipitation and relative humidity, and the high fluctuation in sea water salinity ‎concentrations were the major harmful environmental conditions in the Red Sea shores. Among ‎the both study sites, plants from ‎‏\'‏Al Birk‏\'‏‎ (B) accumulated sodium and chloride with lesser ‎amounts than do plants from ‎‏\'‏Huraidhah‏\'‏‎ (H), especially on warm seasons. Equally, they ‎exhibited the highest accumulation of water soluble carbohydrates and proline and the lowest ‎amount of starch; all these traits are a sign of a high tolerance to the environmental conditions ‎compared to plants from H. In addition, in case of optimal net photosynthetic rate which ‎occurred on date 3, plants from site B showed the lowest transpiration rate and the highest ‎intrinsic water use efficiency compared to plants from site H. These results were in favor of the ‎high tolerance of plants from B compared to those from H site to the Red sea environmental ‎conditions.‎

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