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.

Uptake and accumulation of polycyclic aromatic hydrocarbons in the mangroves Avicennia marina and Rhizophora mucronata.

This study investigated the uptake and accumulation of polycyclic aromatic hydrocarbons (PAHs) in two mangrove species, Avicennia marina and Rhizophora mucronata. We tested the hypothesis that A. marina would absorb and accumulate more PAHs than R. mucronata. One-year old seedlings of both species were subjected to Bunker Fuel Oil 180 for 3 weeks, and the concentration of PAHs was analyzed by gas chromatography-mass spectrometry (GC/MS). The concentration of PAHs was significantly higher in A. marina than in R. mucronata. The major portion of the PAH pool was in roots (96% in A. marina, 98% in R. mucronata) compared to leaves. The dominant PAHs in roots of both species possessed two to three rings and included phenanthrene, anthracene, fluorene, and acenaphthene. In shoots, PAHs in A. marina included phenanthrene, chrysene, anthracene, acenaphthene, benzo[k+b]fluoranthene, pyrene, benzo[a] anthracene, and benzo[a] pyrene, while those in R. mucronata included phenanthrene, naphthalene, fluoranthene, fluorene, and acenaphthene. Phenanthrene was the dominant PAH in roots and shoots of both species. The greater susceptibility of A. marina appears to be due to its greater root length and specific root length, which permit more exposure to oil than R. mucronata. Other contributory factors include root anatomical characteristics such as larger air spaces, lower suberization of root epidermal cells, lower concentrations of polyphenols, tannins, lignin, and a less efficient antioxidative system. This study provides novel information on differences in the uptake and accumulation of PAHs in two contrasting mangrove species.

Are pioneer mangroves more vulnerable to oil pollution than later successional species?

Propagules of Avicennia marina, Bruguiera gymnorrhiza and Rhizophora mucronata were cultivated in rhizotrons (root observation chambers) and subjected to sediment oiling treatments for 409days to determine the effects of oil on root growth. Oiling reduced root length, specific root length, relative root growth rate and root diameter, while specific root volume increased. Oiling reduced root length by 96% in A. marina, 99% in B. gymnorrhiza and 80% in R. mucronata, while specific root volume increased by 34%, 29% and 23% respectively. Relative root growth rate decreased in the oiled treatments by 84%, 80% and 73% respectively. Avicennia exhibits typical root traits of a pioneer species compared to slower-growing later successional species like B. gymnorrhiza and R. mucronata. These traits of A. marina not only allow more rapid establishment of seedlings, but also expose a larger root surface area and therefore greater susceptibility to oil contamination than the other species.

Uptake of polycyclic aromatic hydrocarbons and their cellular effects in the mangrove Bruguiera gymnorrhiza.

The uptake of polycyclic aromatic hydrocarbons and their cellular effects were investigated in the mangrove Bruguiera gymnorrhiza. Seedlings were subjected to sediment oiling for three weeks. In the oiled treatment, the Æ©PAHs was higher in roots (99%) than in leaves (1%). In roots, PAHs included phenanthrene (55%), acenaphthene (13%), fluorine (12%) and anthracene (8%). In leaves, PAHs possessed two to three rings and included acenaphthene (35%), naphthalene (33%), fluorine (18%) and phenanthrene (14%). In the roots, oil caused disorganization of cells in the root cap, meristem and conducting tissue. Oil contaminated cells were distorted and possessed large and irregularly shaped vacuoles. Ultrastructural changes included loss of cell contents and fragmentation of the nucleus and mitochondrion. In the leaves, oil caused dilation and distortion of chloroplasts and disintegration of grana and lamellae. Oil targets critical organelles such as nuclei, chloroplasts and mitochondria which are responsible for cell vitality and energy transformation.