Abstract.The local distribution and seasonal variation of Fe, Pb. Zn, Cu. Cd, Na. K, Ca, and Mg concentrations inCymodocea nodosa(ucria) Aschers., one of the most abundant seagrasses of the area. as well as their concentrations in the sediment and seawater were studied in the Gulf of Antikyra (Greece). The gulf is characterized by a bauxitic substrate and waste discharges from an aluminiumproducing factory. Many of the metals investigated constitute components of the two above‐mentioned metal sources.The mean metal concentrations (± SE) in the seagrass decreased in the order: Ca>Na>K>Mg>Fe>Pb>Zn>Cd>Cu.At the sampling stations A1, A2, A3, B3, and C1, where sufficient data was available for statistical analysis. the concentrations of metals in the plant did not vary significantly among stations (P>0.05).Metal concentrations inC. nodosarevealed two patterns of significant seasonal variation. The first pattern involved Fe, Cd, Na. and Ca and was characterized by high mean concentrations in summer and autumn. A reverse pattern was shown by Pb, Cu. and Mg. These patterns are discussed in relation to the growth dynamics. and leafage of the seagrass. the metal concentrations in the environment. the intermetal correlation, etc.Cu, Cd, Pb, and Ca concentrations in the seagrass were significantly correlated with those in the sediment, whereas a direct relation of plant and seawater concentrations was obtained only for Ca and Mg. The intermetal correlation matrices in C.nodosashowed synergistic interactions between Cd‐Ca, Pb‐Mg, Fe‐Ca, Cu‐Pb, Na‐K, and Na‐Ca and antagonistic interactions between Cd‐Pb, Cd‐Mg, and Pb‐Ca.The Cu, Cd, and Pb concentrations and the maximum Fe concentration inC. nodosain the Antikyra Gulf are high compared with species belonging to theCymodorroideaesubfamily from other geographical areas.SummaryFe, Cu, Pb, Cd, Ca, Na, and Mg concentrations inC. nodosadisplayed significant seasonal variation. The mean concentrations of Fe, Cd, Na, and Ca were high in summer and autumn. In contrast, Pb, Cu, and Mg concentrations were high in December and March. The concentrations of Fe, Cu, Zn, Cd, Pb, Na, K, Ca, and Mg did not vary significantly among the stations A1, A2, A3, B3, and C1of Antikyra Gulf (Greece). Significant correlations were obtained between Ca and Mg concentrations in the seagrass and seawater and between Cu, Cd, Pb, and Ca concentrations in the plant and the sediment. Cd‐Ca, Pb‐Mg, Fe‐Ca, Cu‐Pb, Na‐K, and Na‐Ca showed positive correlations, whereas Cd‐Pb, Cd‐Mg, and Pb‐Ca showed negative correlations in the plant. Finally, the mean metal concentrations inC. nodosadecreased in the order: Ca>Na>K>Mg>Fe>Pb>Zn>Cd>Cu.The concentrations of the heavy metals Cu, Cd, and Pb inC. nodosuin the study area are high compared with species belonging to theCy