An ecological study of seaweeds was carried out bimonthly from April 2015 until June 2016 at five sites located along the Eastern Coast of Alexandria, Egypt (Mediterranean Sea) by examining the conspicuous seaweed community structure and function using percentage cover in addition to the physical and chemical variables of their habitats. This study focused on the newly introduced Phyllymenia gibbesii and its distribution for the first time. A total of 18 seaweed species were identified, which is among them, the opportunistic Ulva lactuca recorded the highest average percentage cover (35.26-80.22%). Phyllymenia gibbesii appeared twice during the study period, with a very low total average cover (0.63%), contributing very little to the main bulk at the time of sampling, thus it cannot be considered as an invasive species. Principal Component Analysis demonstrated that the percentage cover of the algal assemblage was influenced to different degrees by the physical and chemical variables of the ambient seawater. The ecological status of the five sites revealed that they fall between bad and moderate, while the dominance of the opportunistic species and the high load of nutrients in the study area reflected signs of pollution.