Mangrove Zonation: An Examination of Data from Seventeen Riverine Estuaries in Tropical Australia

To characterize mangrove zonation better under conditions innorthern Australia, surveys were undertaken within a numberof riverine estuaries along the eastern coast of Cape York Peninsula,in the Gulf of Carpentaria and at one location in Van DiemenGulf in the Northern Territory. Detailed records were takenof species occurrences along shore normal transects upstreamto tidal limits in each system. A simple numeric procedure developedby Williams, Bunt and Clay (Marine Ecology Progress Series 72 : 283–287, 1991) was applied to the data to definespecies sequential ordering across the intertidal surfaces.Considerable diversity in zonal pattern was found, partly theresult of floristic differences between and along rivers withinthe study area but also arising from variability in the centresof distribution of species across the intertidal surface. Closeexamination of the data suggests the variability to be attributableto the differing responses of individual species to the characterand pattern of environmental controls operating from point topoint locally and at larger scales throughout the mangrove environment.It is concluded that constancy of centres of distribution andof sequencing order under conditions in tropical Australia arenot to be expected. At the same time, within the range of alongtransect species distributions, conditions are likely to beencountered which permit individual species, whether rarelyor not, to occupy all or most of the intertidal surface. Anyother pattern of distribution is interpreted to represent conditionswhich, at least to a degree, are limiting for the species inquestion. In mangrove environments of considerable diversity,only extensive survey can be expected to reveal the full extentof zonal pattern in the associated vegetation. Mangroves; zonation; variability; riverine estuaries; Australian tropics