Fish distribution and ontogenetic habitat preferences in non-estuarine lagoons and adjacent reefs

We surveyed fish distribution in three lagoons and adjacent forereefs in the British Virgin Islands recording about 28,000 fish from 40 families and 118 species. Canonical correspondence indicated that rock, sand, fleshy algae, gorgonians, mangroves and live hard coral were the most important habitat types influencing fish assemblage composition. About 47% of fishes occurring at more than 10 stations displayed evidence of ontogenetic partitioning between reefs and lagoons but post-settlement ontogenetic life history strategies were quite varied depending on the species. For example Chaetodon striatus juveniles occurred exclusively in lagoons and all sexually mature adults were found on reefs. Some differences were less pronounced as seen in Halichoeres bivittatus where individuals of all sizes occurred on reefs and lagoons, but when analysed it was found that reefs had larger individuals than lagoons. Some species, such as Acanthurus bahianus, were primarily reef species whose juveniles also used lagoon habitats while others, such as Gerres cinereus, were generally lagoon species whose adults occasionally moved onto reefs. Even with all this variation in life-history strategies, all the species that exhibited bay-reef partitioning used the lagoons as juveniles then moved onto reefs as adults and not vice versa, supporting the hypothesis that bays are important nursery areas for reef-dwelling fishes. These results show that a detailed review of the natural life-history strategies and habitat requirements are required before making further generalisations about the role of near-shore habitat types as nurseries for reef fishes. This is especially important given the rapid changes in tropical near-shore habitats around the world.