Large, ancient trees hold ecological significance worldwide due to habitat provisioning for fauna (hollows and gaps), their role in supplying seeds, propel new tree growth, maintain healthy soils and capturing carbon. Ancient trees of Avicennia marina in Moreton Bay, Queensland have large hollows within their trunk and branches, providing sheltered habitats for a variety of fauna, including vulnerable and endangered species. However, their abundance and distribution are not known, despite their importance for management of biodiversity in the urban setting of Moreton Bay. Transects throughout Moreton Bay’s intertidal wetlands located and characterised large A.marina, discovering patterns in their distribution and distinctive morphological characteristics. Most large, ancient trees were located in the seaward fringe or in areas adjacent to terrestrial environments in reserves. Large. ancient mangroves had significantly proportionally larger canopy extents and more stems per individual than smaller trees and had higher numbers of hollows than smaller trees. Basal area growth rate was similar in both large and smaller trees and was dependent upon rainfall. Mangrove protection and management could focus on large ancient A. marina trees because of their ecological importance for faunal habitat provision in mangroves surrounding urban populations.