Halong Bay is host to two ecosystems: a tropical, moist, evergreen rainforest ecosystem; and a marine and coastal ecosystem.
The many islands that dot the bay are home to a great many other species, including (but likely not limited to): 477 magnoliales, 12 pteris, 20 salt marsh flora; and 4 amphibia, 10 reptilia, 40 aves, and 4 mammalia.