It is one of the curious features of mangroves that the object one sees occupying the place of an apparently ripe fruit is neither fruit nor seed. Large numbers of fruits develop and most of these ripen successfully. But then the seed germinates in the fruit, and develops a long hypocotyl, so that what falls from the tree is better called a propagule (in effect, a germinating seedling). In the black mangrove the hypocotyl is about the size, shape and colour of a modest Havana cigar, and so not perfectly adapted to making the most of opportunities for rooting in the mud. In other mangroves, the hypocotyl develops in such a way that the weight is at one end, making it more likely that the propagule will land upright in the mud, with enough force to lodge securely against being swept away by currents and tides. If the propagule (of any mangrove) is swept out to sea, it will soon grow a few pairs of leaves, which act as sails while it is carried to another shore.

One of the major problems for any plant growing in the highly saline conditions of a mangrove swamp is how to get rid of excess salt. Black mangroves achieve this by depositing the salt in old leaves, which are eventually killed by the concentrated "refuse" they contain. The leaves go yellow and fall, taking the excess salt with them, and so visitors to a mangrove swamp will see healthy trees dropping leaves at any and all times of year. Almost as soon as a leaf falls, one of the crabs ( Uca spp., and possibly others) in the swamp will quickly emerge, grab its prize and dash back to its hole, as these fallen leaves are a major item in the crabs' diet.

Another problem with being a mangrove is that their roots are in permanently waterlogged mud, but still need some air to survive. Different mangroves have evolved different structures to deal with this, such as the prop-roots of Rhizophora or the pencil-roots (pneumatophores) of Avicennia. In Bruguiera, the "breathing-roots" are knee-like structures projecting some 30 cm above the mud and supported on two or more roots. The top of each of these develops a callus-like tissue through which the necessary air exchange takes place.

A report from the Ryukyu Islands (Japan) suggests that Bruguiera gymnorrhiza is bird-pollinated, which would make sense of the copious nectar secreted by the flowers. However, it seems that Black Mangroves on Inhaca Island, Mozambique, are pollinated by bees.

Other residents of local mangrove swamps include mud-prawns (Upogebia africana) and various snails, of which the most conspicuous is Cerithidium decollata. Some dozens of individuals of this species will be found half-a-metre and more above ground level on each tree trunk. Although crocodiles and sharks are reported from the waterways in mangrove swamps, probably the most dangerous inhabitant is Anopheles gambiae, one of the main mosquito vectors of malaria.