The Theme 5.3 study was undertaken to improve our understanding of the spatial and temporal patterns in seagrass composition, abundance and reproductive phenology in the Pilbara region. Key environmental parameters, especially light, that influence seagrass survival and can be altered by dredging were also characterised.
From August 2013 to March 2015 (18 months), surveys of seagrass abundance were undertaken in the Exmouth Gulf region. The locations surveyed (South Muiron Island, Bundegi and Exmouth Gulf) encompassed a range in water clarity from clear to turbid. Less frequent surveys were undertaken at other locations in the Pilbara: Thevenard Island, Rosemary Island and Balla. Measurements of seagrass abundance were also obtained from monitoring conducted as part of the dredging and dredge-spoil management plan for Chevron Australia's Wheatstone Liquefied Natural Gas (LNG) Project.
During each survey measurements were made in the field, photographs were taken or samples were collected in order to measure the following variables:
1. percentage cover of seagrass and other benthos;
2. above- and below-ground biomass, shoot density, leaf length, leaf width and number of flowers;
3. density of seagrass seeds;
4. sediment grain size;
5. stable isotope ratios (Ô13C and Ô15N) of seagrass leaf tissue; and
6. water quality (light, conductivity, temperature, salinity, nutrients, suspended particulate matter and chlorophyll).