Quantifying native and invasive oyster distributions in the iconic urbanised Port Jackson estuary

Many of the world’s major cities are on the coast or in large estuaries. Such urbanisation results in the pollution of estuaries with a suite of toxicants. Increased marine traffic and foreshore alterations in urbanised... [ view full abstract ]

Many of the world’s major cities are on the coast or in large estuaries. Such urbanisation results in the pollution of estuaries with a suite of toxicants. Increased marine traffic and foreshore alterations in urbanised estuaries all contribute to a significant loss of biodiversity and provide opportunities for invasion by non-indigenous species. The establishment of baselines and monitoring key biogenic habitat forming organisms is essential to retaining the biodiversity in estuaries. This study assessed the along shore distribution and species composition of the ecological keystone oyster populations in Port Jackson. Port Jackson (Sydney, Australia) is among the most heavily urbanised estuaries in the world, however the current state of oyster populations remains unknown. We tested hypotheses that 1) the size, abundance and relative proportion of the oysters Crassostrea gigas and Saccostrea glomerata would differ dependent on the location in the estuary; and 2) habitat type; natural or artificial. To test these hypotheses, 16 locations were selected throughout the estuary, encompassing both natural and artificial habitats. Abundance and distribution of oysters was sampled at each site using random quadrats, and individuals were collected to determine their identity and size. A lysosomal destabilisation assay was conducted on oysters from six locations (three impacted, three control) to confirm the presence of bio-available toxicants. It was found that the abundance of oysters was significantly different among locations and sites. Oysters were more abundant, but smaller in the eastern reaches of the estuary, while in the west, oysters were less abundant but larger. The invasive C. gigas was found to be more prevalent than previously recorded in all other NSW estuaries, and larger than the native S. glomerata. Populations of C. gigas displayed a patchy distribution. In some cases at highly contaminated sites (confirmed by high levels of lysosomal destabilisation), C. gigas comprised the majority of the assemblage. This study is the first to identify and quantify the extent of the invasive C. gigas in Port Jackson and provides a solid base for gauging any changes in Port Jackson oyster populations as a result of further urbanisation.