Are populations of coral reef fish open or closed?

Dispersal plays a crucial role in several aspects of the biology, management and conservation of many species, including coral reef fish and other demersal marine organisms with pelagic larval stages. To know the origin of propagules that replenish benthic populations is a major challenge, yet, whereas earlier studies emphasized the broadly extensive dispersal of reef fish larvae, recent publications have emphasized the extent to which these larvae succeed in returning to their natal populations. Here, we critically analyse the evidence concerning the dispersal of coral reef fish, and conclude that: (1) at present, the extent to which reef fish populations are open or closed must be regarded as unknown; and (2) further improved research is likely to confirm that larval dispersal structures populations into more or less open populations depending on the particular attributes of species, physical oceanographical systems in which they occur and the scale at which the question is posed.