MANGROVE HABITATS AS NURSERIES - UNIQUE ASSEMBLAGES OF JUVENILE FISH IN SUBTROPICAL MANGROVES IN EASTERN AUSTRALIA

A total of 53 species of juvenile fish were caught over a 2 yr study p eriod in 2 mangrove lined estuaries in Moreton Bay, eastern subtropica l Australia. Comparing juvenile fish communities among mangrove forest s, seagrass beds and mudflats identified significant differences in sp ecies richness and abundances of juveniles. Seagrass communities compr ised distinct species of resident and nonresident fish species of litt le economic importance. Mangrove forests and mudflats had many shared species (but mangrove forests were dominated by smaller or younger juv eniles in greater abundances; Laegdsgaard unpubl. data). Mudflat habit ats appear to be transition zones between juvenile and adult habitats. Only 4 species were exclusive to seagrass whereas 27 species were exc lusive to the mangrove/mudflat habitat. Juveniles of 7 of the 10 comme rcially harvested fish species in Moreton Bay were found in greatest n umbers in mangrove forests. Salinity, temperature and turbidity were s imilar in all habitats so could not account for differences in habitat choice of juvenile fish. Most juvenile fish in mangroves during summe r were nonresidents and species richness and abundance were highest in summer and lowest in winter. There were significant differences among sites and years in the numbers of species and individuals; however, t he trends were similar and demonstrated clearly that mangrove sites wi thin Moreton Bay play a more important role and have greater potential as nursery habitats than do adjacent habitats. Preferential selection of mangrove habitats by juvenile fish, particularly commercial specie s, indicates a need for conservation.