Western Australian marine fish communities consist of two broad species pools: a tropical Indo-Pacific fauna, and a largely endemic temperate fauna. Stochasticity was identified as a prominent process involved in community assembly, at both taxonomic and functional levels of community organisation. Opposing latitudinal gradients in dispersal limitation and environmental filtering are superimposed over this pattern, with dispersal limitation acting more strongly in the tropics, and environmental filtering stronger in temperate communities. Temperate communities also exhibited greater ecological specialisation and stronger heterospecific co-occurrences. The latitudinal gradient in these processes may be a result of the differing evolutionary histories of the communities.