A review of bioturbation and sediment organic geochemistry in mangroves

Mangroves, which are a group of salt tolerant plant community growing in the transition zones of fresh and marine water systems, play an important role as sediment trap. In mangrove ecosystems, litterfall accumulates as organic carbon and nutrients over the sediment surface, where bioturbation profoundly affects the sediment biogeochemistry. Here, we provide a brief overview of the bioturbating organisms in mangroves and discuss their roles in controlling the sediments organic biogeochemistry. The mangrove soils formed on marine alluvium is transported as sediment and deposited by the river and sea. This type of soil is typically saline, anoxic, acidic and periodically waterlogged and composed of different combinations of sand, silt, clay and mud. The decapod crustaceans, specifically, crabs are the main bioturbating organisms in mangroves ecosystem. Moreover, amphipod, callianassid, penaeid shrimp, alpheid shrimp, thalassinid lobster, sipunculid worm, bivalves and bony (teleostei) and shark-like (elasmobranchii) fishes contribute to the biogenic dispersal of sediment particles. Bioturbation processes by these organisms are reported to control nutrients and carbon cycling across the sediments. Activities such as feeding, burrowing and ventilation also influence the decomposition rate of sediment organic matter and nutrient exchange. However, anthropogenic pollution from power plant effluent (hot-water outflows), heavy metals, pesticides, polychlorinated biphenyls (PCBs), industrial pollutants, eutrophication (fertilizers and sewage) and oil spills are major concerns impacting the mangrove sediments and ecosystems.