Trace Metal Bioaccumulation Patterns in Avicennia marina Mangroves from the Red Sea and Arabian Gulf: A Comparative Study

This study presents the first comprehensive investigation of trace metal accumulation in the tissues of Avicennia marina (mangrove) from two ecologically distinct regions: the eastern coast of the Red Sea and the western coast of the Arabian Gulf. Metal concentrations were analyzed in various plant tissues, including stems, leaves, buds, flowers, seed coats, seed flowers, embryos, and cotyledons. Fourteen trace metals—Al, As, Ba, Cd, Co, Cr, Cu, Fe, Li, Mn, Ni, Pb, V, and Zn—were quantified to assess bioaccumulation patterns and establish comparative correlations between mangrove communities in both regions. Statistical comparisons revealed higher overall metal accumulation in A. marina tissues from the Red Sea compared to the Arabian Gulf (p < 0.05). A striking pattern of metal concentration was observed, with buds showing the highest levels, followed by seed flowers, flowers, embryos, seed coats, and cotyledons, while stems and leaves exhibited regionally variable metal loads. Red Sea mangroves showed significantly higher metal concentrations in stems and leaves than their Arabian Gulf counterparts (ANOVA, p < 0.01). The metal accumulation hierarchy in A. marina was determined to be: Fe > Al > Zn > Mn > Cu > Ba > Ni > Cr > As > V > Li > Cd > Co > Pb. Importantly, this study is among the first to include reproductive tissues—buds, seed flowers, and embryos—in assessing metal bioaccumulation, offering new insight into tissue-specific uptake mechanisms. Principal component analysis revealed that stem samples from the Red Sea were predominantly enriched in Al, Fe, Mn, Li, and V, whereas bud samples from the Arabian Gulf showed higher concentrations of Ba, Cu, Cr, Ni, and Zn. This study underscores the selective metal accumulation in specific plant tissues and highlights the potential of A. marina as a bioindicator of trace metal pollution, with significant differences between the Red Sea and Arabian Gulf ecosystems.