Biophysical Processes in the Torres Strait Marine Ecosystem 2004

These data are the result of Geoscience Australia survey 266 to the central Torres Strait region, with the survey being the first of two by Geoscience Australia carried out in 2004. They form part of a larger field-based program managed by the Torres Strait CRC aimed at identifying and quantifying the principal physical and biological processes operating in Torres Strait. The impetus for the program is the threat of widespread seagrass dieback and its effects on local dugong and turtle populations and the implications for indigenous islander communities. The principal aim of the survey was to investigate the seabed geomorphology and sedimentary processes in the vicinity of Turnagain Island and to infer the possible effects (if any) on the distribution, abundance and survival of seagrasses.

The Turnagain Island region was chosen because it is a known site of recent widespread seagrass dieback. The survey consisted of a detailed geophysical survey using swath (multi-beam) sonar and shallow seismic equipment that was supplemented with a detailed sampling program consisting of 301 near-bed water samples, 54 seabed grabs, 5 vibrocores and 69 camera stations. Four oceanographic moorings were also deployed for the duration of the survey to measure the local tide, wave and wind-driven currents. A regional survey was initially undertaken, followed by a detailed study of two areas: Area A - located approximately 2.5 km SW of Turnagain Island which contained sand ridges and seagrass beds, and Area B - located approximately 2.0 km SE of Turnagain Island which contained sandwaves and no seagrass beds.

In a new application of the swath (multi-beam) data, the total volume of sediment transported during the survey was estimated from changes in the high-resolution seabed bathymetry collected during the repeat surveys.

Preliminary results of the study found that seagrasses in the region are subject to frequent and significant changes in environmental conditions, with implications for limited dispersal and survival. A follow-up survey was undertaken in October 2004.