Leaf litter, pneumatophores, saplings and patches of macro-algae are common characteristics of habitats in mangrove forests. The amounts of these vary among different parts of mangrove forests. In Port Jackson, some parts of forests under the canopy of trees appeared to have more saplings, longer pneumatophores and greater amounts of leaf litter and macro-algae than did other similarly shaded parts of the forest. The former also appeared to have greater densities of snails, Ophicardelus spp. and Salinator solida, which was confirmed by quantitative sampling. Two field experiments were carried out, in which the amount of litter or algae and the length of the pneumatophores, were manipulated to test six alternative models about influences of these features of habitat that might explain these patterns. In each experiment, both species decreased rapidly in plots with reduced litter and showed no response to the length of the pneumatophores. In the first experiment, there was no response to reductions of algae, but in the second experiment, each species showed a decrease in density when algae were reduced. The implications of these rapid responses to changes in small-scale features of habitat are discussed with respect to managing disturbed habitats.