Mangrove As A Bioindicator For Environmental Pollution In The Coastal Marine Environments-Review

Abstract

Mangrove stand components have been used widely as bioindicators for different types of environmental pollution including heavy metals, organic pollutants and hydrocarbons as as well as in the detection of ozone depletion conditions. Heavy metals and organic pollutants such as herbicides concentrate in leaves, pneumatophores (aerial roots) and bark of the stems and branches. This is associated with succulence in leaves, which lead eventually to their fall. Heavy metals would be released after the diagenesis of the litter and added to the pollutant budget again. Mangrove stands trap and accumulate fine sediments, which eventually cause the development of high-density pneumatophores. Furthermore, heavy metals accumulate in the few upper centimetres of the mangrove soil layer. The ability of the soil to heavy metals retention depends on their texture, organic matter content, composition, redox potential, pH, salinity and Al, Fe and Mn contents.

Mangrove trees have been used to screen for mutagens in tropical environments and was found that red mangroves have the reproductive traits that allow the detection of nuclear and cytoplasmic mutation in the field in the same way as colonies of bacteria or yeast are screened for mutation in the laboratory. The chlorophyll-deficiency has been used also as a genetic end-point in plant mutation in areas polluted with oil. Oil pollution is associated with increased number of pneumatophores, generation of malformed leaves and fruits and decrease in litter production. Furthermore, mangrove developed highly branched pneumatophores rather that the normal pencil-shaped. Experimentation on the effect of ultraviolet radiation on the development of the seedlings of the mangrove Rhizophora has indicated that their growth was generally reduced with exposure to high UV with shoot elongation. The integrity of the mangrove ecosystem can be used as a simple bioindicator for a wide range of pollutants with a high efficiency and a minimum cost.