AbstractsBiology & Animal Science

The hierarchical effects of anthropogenic impacts and natural filters on the distribution of freshwater mussels in the Hawkesbury-Nepean River, NSW, Australia

by Meredith A. Brainwood

Institution: University of Western Sydney
Degree: PhD
Year: 0
Keywords: freshwater mussels; water quality; water; pollution; New South Wales; Hawkesbury-Nepean River (N.S.W.); Hawkesbury River; Nepean River
Record ID: 1062709
Full text PDF: http://handle.uws.edu.au:8081/1959.7/489759


In comparison with North America, there is a poor level of taxonomic diversity in the Australian freshwater mussel fauna. Seventeen endemic hyriid species have been recorded in this country, while over 30 species have been recorded from one reach of a US river. While there have been no extinctions recorded among Australian mussel species, there are several species under threat, and mussel populations in many river systems are in serious decline. One of these catchments, the Hawkesbury-Nepean River, is considered to be among the most highly impacted of the eastern coastal rivers. Mussel populations in this river are believed to have declined in density and distribution, but to date this observation has been based on anecdotal, rather than scientific, evidence. This study aims to address the dearth of knowledge regarding population ecology for hyriid species by compiling a detailed assessment of mussel species, densities and sizes for a series of 100 sites throughout the greater Hawkesbury-Nepean River. Mussel populations were sampled concurrently with a range of physical habitat variables to identify natural and anthropogenic factors that may be important for defining the observed mussel assemblage structure. The results from these assessments were used to develop a hierarchical model that ranked the relative importance of these physical habitat variables in determining mussel distribution. An initial survey of sites in the Nepean River indicated that a high level of riparian disturbance was strongly related with decreased mussel density, and often with the apparent absence of mussels from many sites. Distribution of species and density of mussel assemblages were strongly associated with geomorphic reach type, so that different reaches supported different suites of mussel species. Presence of mussels was strongly associated with annual maximum dissolved oxygen, minimum total nitrogen, and minimum conductivity. Each species was associated with different annual patterns of water quality. Velesunio ambiguus were most frequently associated with maximum dissolved oxygen, and minimum conductivity and total phosphorus. In contrast, Hyridella depressa were not linked with dissolved oxygen patterns, but were negatively affected by turbidity and total phosphorus. Hyridella australis were associated with annual maximum dissolved oxygen, and not apparently affected by other aspects of water quality. Densities of mussels were compared with single samples for water quality at a second set of sites. Data from this study suggested that at higher densities, mussel populations impacted water quality, rather than water quality impacting mussel populations. The results indicated that at higher densities, mussels were able to favourably impact on water quality, reducing levels of phosphorus in the water column. Both small and large impoundments were seen to influence the composition of mussel assemblages. The presence of a large impoundment, mid catchment, was strongly associated with the absence of mussels upstream, and the presence of…