The conservation significance of estuaries: a classification of Tasmanian estuaries using ecological, physical and demographic attributes as a case study

Estuaries arguably represent the most anthropogenically-degraded habitat-type on earth, with few estuaries in temperate and tropical regions existing in a near pristine state. Conservation of estuarine biodiversity requires recognition that different estuary types are subjected to particular types and levels of human impact. To protect assemblages associated with all estuary types in Tasmania, Australia, the conservation significance of the 1 1 1 large- and moderate-size estuaries in the island state were assessed by firstly categorising estuaries into nine groups on the basis of similarities in physical attributes. These attributes were quantified using GIS maps of estuaries and their catchments and held-collected data, with separation of groups primarily reflecting presence of a seaward barrier, tidal range, salinity, estuary size and river runoff. The adequacy of the physical groups as surrogates for biological patterns was assessed by comparison with data on the distribution of 390 macrobenthic invertebrate taxa in 48 Tasmanian estuaries and 101 beach-seined fish species in 75 estuaries. Multivariate analyses indicated that six of the nine estuarine groups based on physical data were useful for categorising biological relationships between estuaries, but that three groups required modification to prove more biologically meaningful. Within each of the estuarine groups, human population, landuse and land tenure data were used to assess the level of anthropogenic disturbance to each estuary, and the estuary with least disturbance in each group assigned highest conservation significance. Recommendations have been made to create a comprehensive system of estuarine protected areas by legislating to protect species within the nine representative estuaries of highest conservation significance, plus an additional estuary with exceptional species richness. Such a system of protected areas should conserve the range of estuarine biodiversity with minimal disruption to existing estuary users. (C) 2000 Elsevier Science Ltd. All rights reserved.