Mangroves are a type of estuarine swamp environment dominated by mangroves and other saltwater-tolerant trees. All mangrove areas on Guam are located in the southern half of the island, with largest concentrations found along the eastern shores of Apra Harbor and smaller zones present in Merizo and Inarajan.

Guam's mangrove species include Rhizophora mucronata, R. apiculata, Bruguiera gymnorrhiza, Avicennia marina, Lumnitzera littorea, N. fruticans, Xylocarpus moluccensis, Heritiera littoralis, H. tiliaceus and Acrostichum aureum (Fosberg, 1960; Moore and others, 1977).

Mangroves are important habitats for juveniles and adults of many fish species, as well as many specialized aquatic invertrebrates. In addition, they act as filters, trapping sediment from rivers before it can be deposited on sensitive coral reef habitat. Many species of migratory shorebirds also use Guam’s mangrove areas as feeding and resting areas.