Salinity exacerbates oil contamination effects in mangroves

The effects of salinity (10 and 50% seawater) and oil in combination on three mangroves, Avicennia marina, Bruguiera gymnorrhiza, and Rhizophora mucronata, were investigated. In all species, plant height, number of leaves, and CO₂ exchange were generally higher in 10% than in 50% seawater. Salinity and oil decreased plant height, number of leaves, chlorophyll content, and CO₂ exchange, with reductions being greater at the higher salinity. In a second experiment, the effects of salinity (0, 10, and 50% seawater) and oil on concentrations of ions, polycyclic aromatic hydrocarbons (PAHs), leaf ultrastructure, and salt secretion in A. marina were investigated. Salinity and oil in combination increased concentrations of Na⁺ but decreased those of K⁺, Ca²⁺, and Mg²⁺. PAHs caused damage to cell membranes, disrupted ion concentrations, and reduced salt secretion. This study demonstrated that increase in salinity reduces growth of mangroves and that salinity and oiling in combination exacerbate growth reduction. In A. marina, oil was absorbed and translocated to the leaves where it disrupted membranes, ion accumulation, and salt secretion.