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 period in 2 mangrove lined estuaries in Moreton Bay, eastern subtropical Australia. Comparing juvenile fish communities among mangrove forests, seagrass beds and mudflats identified significant differences in species richness and abundances of juveniles. Seagrass communities comprised distinct species of resident and nonresident fish species of little economic importance. Mangrove forests and mudflats had many shared species (but mangrove forests were dominated by smaller or younger juveniles in greater abundances; Laegdsgaard unpubl. data). Mudflat habitats appear to be transition zones between juvenile and adult habitats. Only 4 species were exclusive to seagrass whereas 27 species were exclusive to the mangrove/mudflat habitat. Juveniles of 7 of the 10 commercially harvested fish species in Moreton Bay were found in greatest numbers in mangrove forests. Salinity, temperature and turbidity were similar in all habitats so could not account for differences in habitat choice of juvenile fish. Most juvenile fish in mangroves during summer 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, the trends were similar and demonstrated clearly that mangrove sites within 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 species, indicates a need for conservation.