9. Australian Mangroves: Anthropogenic Impacts by Industry, Agriculture, Ports, and Urbanisation

Australia has an extensively mangrove-lined coast and even though it has a relatively low human population compared to the length of its coastline, there have been significant impacts on its mangroves. Belonging to the Indo-Malesian Group of the Old World Mangroves, the most species-rich region of the World, Australia uniquely carries the Old World mangroves into a Tropical arid climate along its west coast and to a humid Tropical to Temperate climate along its east coast. In addition to being species-rich, Australia manifests a large variability of coastal types that result in a multitude and heterogeneity of suitable habitats and a richness in mangrove assemblages. As such, industrial, urban, port, and agricultural impacts are occurring on mangrove systems that globally have comparatively high environmental, ecological, and bioheritage value. Mangrove ecosystems are complex involving interactions between stratigraphy, hydrology, hydrochemistry, biological components, and anthropogenic activities which interface with these as overt and covert impacts. Overt impacts involve obvious destruction or alteration of mangroves such as clearing, burial by landfill for industrial, urban, recreational, and agricultural estates, cutting of channels, construction and expansion of harbours, bunding of natural channels and oil spills. Covert impacts are not as visible, and usually involve the alteration of hydrology and hydrochemistry of mangrove system by drainage basin contamination, and the alteration of salinity regimes, amongst others.

Twenty areas of mangrove coasts, selected from a variety of coastal types, climate and oceanographic settings, and various mangrove biodiversity settings, are provided to illustrate the range of impacts that have occurred. The impacts are graded as to being major, medium, minor, or innocuous, based on the extent and intensity of the impact(s), and the regional, national or global significance of the mangroves at the site. The extent and intensity of the impact on mangrove vegetation are assessed taking into account the spatial extent of mangrove vegetation, the changes sedimentologically, geochemically, and hydrologically/hydrochemically, and any changes in the benthic biota in terms of their composition and abundance. Of the 20 sites, nine areas are assessed as having had major impacts on their local mangroves.