Human activity increasingly impacts coastal marine ecosystems through urban discharges and the use of the ocean as a dumping ground, leading to elevated pollution levels. This research aimed to determine trace metal element (TME) concentration profiles (Cd, Cu, Pb, and Zn) in the water and leaves of the Posidonia oceanica seagrass bed in the Gulf of Annaba (Algeria). Water and plant samples were collected at four sampling sites selected for their hydrodynamics and proximity to effluents flowing into the Gulf. Flame atomic absorption spectrophotometry was used to identify TMEs. The results showed that Cd, Pb, Zn, and Cu are present in all seawater samples. The measured TME concentrations are listed in descending order where Pb is followed by Zn, Cu, and Cd. The order of enrichment in both leaf types (adult and intermediate) of P. oceanica is Pb > Zn > Cu > Cd. S2 exhibited the highest lead concentrations, while S4 had the lowest. The BCF calculation revealed that our plant concentrates Cd, Pb, Cu, and Zn in various leaves within the biotope. The Fisher test (one-factor ANOVA) results showed significant differences in the concentrations of measured TMEs in the three compartments (water, FI, and FA) for Cu, Cd, and Pb and significant differences for Zn. However, for the four measured TMEs, the two-factor ANOVA test revealed no significant differences between the station-compartment groups.