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

Abstract

To characterize mangrove zonation better under conditions in northern Australia, surveys were undertaken within a number of riverine estuaries along the eastern coast of Cape York Peninsula, in the Gulf of Carpentaria and at one location in Van Diemen Gulf in the Northern Territory. Detailed records were taken of species occurrences along shore normal transects upstream to tidal limits in each system. A simple numeric procedure developed by Williams, Bunt and Clay ( Marine Ecology Progress Series 72: 283–287, 1991) was applied to the data to define species sequential ordering across the intertidal surfaces. Considerable diversity in zonal pattern was found, partly the result of floristic differences between and along rivers within the study area but also arising from variability in the centres of distribution of species across the intertidal surface. Close examination of the data suggests the variability to be attributable to the differing responses of individual species to the character and pattern of environmental controls operating from point to point locally and at larger scales throughout the mangrove environment. It is concluded that constancy of centres of distribution and of sequencing order under conditions in tropical Australia are not to be expected. At the same time, within the range of along transect species distributions, conditions are likely to be encountered which permit individual species, whether rarely or not, to occupy all or most of the intertidal surface. Any other pattern of distribution is interpreted to represent conditions which, at least to a degree, are limiting for the species in question. In mangrove environments of considerable diversity, only extensive survey can be expected to reveal the full extent of zonal pattern in the associated vegetation.