Edith Cowan University, Research Online, Perth, Western Australia
Abstract
The soft-substrate bivalves of the Swan Estuary were evaluated for their suitability as biological indicators. The major requirement of a biological indicator is that a response to changing conditions can be shown. Demonstrating that bivalve community and populations respond to changing environmental conditions within The Estuary would fulfill this criteria. To make this assessment the study conducted a quantitative sampling program which established the current structure of the near-shore soft-substrate bivalve community and this was compared with the community established in 1973-74. To evaluate the predictive potential of bivalve structure as an indicator, major environmental conditions in the Estuary were measured and related to bivalve distribution, abundance and biomass. TI1e utility of bivalves as indicator species in causal experiments was also assessed by means of a toxicity test conducted in the laboratory. Tills study found significant differences in the current bivalve community compared with that established in 1973-74. Three species have been added to the Middle Estuary community, two of which now dominate. Possible relationships between these changes and alterations to environmental conditions within the Estuary over the same period i.e nutrient enrichment and changes in hydrology, were examined but conclusions were speculative only. The current bivalve community appears to represent the major biotic divisions within The Estuary and relationships were found with the presence of seagrass, phytoplankton biomass, fine particulate organic matter and sediment grain-size composition. A causal relationship to the toxicity of chromium was demonstrated in the laboratory. The processes of measuring population and community structure, and of handling and manipulating bivalves both in the field and the laboratory were shown to be time- and cost-efficient. Their ease of sampling, abundance and widespread distribution affords bivalves potential as biological indicators within the Swan Estuary
