Oil Pollution in Mangroves: A Review

Abstract

Oil pollution effects on mangroves may be categorised as lethal (acute) and sublethal (chronic). Lethal effects usually occur at high oil dosage, which smothers and kills the entire root system and causes mass mortality. Sublethal effects occur when oil enters with tidal inundation or becomes trapped in sediments, resulting in prolonged deleterious effects that do not cause mortality. Long-term sublethal effects, however, are poorly understood. This review summarises the current information on the sublethal effects of oil pollution on mangroves. It begins by examining the characteristics of oil and then evaluates the effects of oil on propagules, roots, and leaves, as well as the underlying ecophysiological mechanisms of toxicity. Within cells, PAHs target organelles responsible for cell metabolism and energy relations, including the nucleus, mitochondria, and chloroplasts. Oil disorganises and disintegrates the lipid components of membranes, increasing their permeability. Responses of mangroves to oil include leaf senescence, defoliation and reductions in photosynthesis and biomass. Oil also decreases reproductive capacity, inhibits germination, induces mutations, and causes the development of anomalous growth forms, as well as oxidative stress and mortality. Abnormal root development at the lower portions of the stem and chlorophyll-deficient propagules are suggested as biological indicators of oil contamination in mangroves.