A detailed benthic faunal and introduced marine species survey of Port Davey, Bathurst Channel and Bathurst Harbour in SW Tasmania

Brief description

This study aims to undertake a comprehensive survey of the benthic fauna of Port Davey – Bathurst Harbour and adjoining Payne Bay, James Kelly Basin and Hannant Inlet. This will provide important information on the composition and structure of benthic faunal communities and the distribution of any introduced species amongst the benthos.

In February/ April 2007 invertebrate faunal communities were sampled at 70 locations throughout the system – with the greatest intensity of sites located within Port Davey, Bathurst Channel and Bathurst Harbour.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Seventy locations were sampled throughout the Port Davey – Bathurst Harbour system (see report for map of locations). Sites were representative of a range of locations, depths and sediment types.
Depth was measured from the surface using a depth sounder. Benthic invertebrate communities were sampled from the surface using an Eckman grab (in silty and muddy sediments) or a Van Veen grab in sandy sediments. At each site three replicate grab samples were collected and amalgamated in the field after sieving through a 1.0 mm mesh sieve then fixed in buffered 10% formalin seawater solution. An additional grab sample was collected for sediment physical and chemical analysis (C. Reid, Queens University, Canada). Surface and bottom water salinity were
recorded at each location using a conductivity-salinity probe (not included in this dataset). The geographical position of
each site was marked using GPS.

At a subset of sites (6) sediment was collected to determine the presence of Gymnodinium catenatum and Alexandrium dinoflagellate cysts in Bathurst Harbour and the eastern end of Bathurst Channel. G. catenatum cysts were previously recorded from the western end of the channel (Aquenal 2003). Sediments were stored at 4 °C and processed by the Harmful Algal Blooms Research Group, University of Tasmania.

Sites 1-47 were sampled from 19-28 February whilst based out of Melaleuca. Sites 50-72
were sampled from 22-26 April using a chartered vessel working in and around Port Davey. The depth of samples collected ranged from 1.5–29 m (the limit at which the grabs effectively operated). All sites sampled were unvegetated with exception of PD53 in James Kelly Basin where the benthos was dominated by dense beds of the green alga
Caulerpa trifaria.

Lab methods
Invertebrate specimens were identified to species, where possible, and then counted for each site using a dissecting microscope. Specialist taxonomic advice and identifications were provided by G. Walker-Smith, L. Turner and K. Moore (Tasmanian Museum and Art Gallery); R. Wilson, T. O’Hara, J. Taylor, D. Staples and G. Poore (Museum Victoria) and A. Hirst, L. Meyer, G. Edgar and C. McCleod (TAFI). Ostracod crustaceans could not be identified beyond the class-level, however, there are no introduced ostracod species currently listed (Hayes 2005 database). Species lists were cross-referenced against a list of 133 introduced and 175 cryptogenic marine species currently listed by CSIRO’s Centre for Introduced Marine and Pest Species as established within Australia (Hayes 2005 database). In the case where species identifications were not initially possible, specimens were sent to
specialist taxonomists where the genus or family of the specimen coincided with known introduced or cryptogenic species. For example, the sabellid worm Euchone sp. was determined to be the native species Euchone variablis rather than the introduced species Euchone limnicola. In many cases the absence of full species names for specimens is a reflection of the poor state of taxonomic knowledge of many groups in southern Australia – particularly crustaceans and polychaetes. This increases our uncertainty about the origin of specimens.

Sediment cores were examined for dinoflagellate cysts using standard methods developed by the Harmful Algal Blooms Research Group, University of Tasmania. Heavier particles (including cysts) were separated from finer organic silt particles using a sodium polytungstate density separation technique. These heavier fractions were then sorted under a microscope and any dinoflagellate cysts present identified.

Notes

Credit
Natural Heritage Trust

Credit
Natural Resource Management South (NRM), NRM Project No. WPD3

Purpose
Past research in the region has focussed primarily on the hydrology of the estuary, in addition to the ecology of plankton, fish and reef communities, however, there is little known about the ecology of benthic soft-sediment communities – the major habitat in this system. This study aims to at least partially fill this gap by undertaking a comprehensive survey of the benthic fauna of Port Davey – Bathurst Harbour and adjoining Payne Bay, James Kelly Basin and Hannant Inlet.