WAMSI Node 1.1.3 - Perth soft sediment studies

Twenty-nine sites have been surveyed: 13 in Marmion Marine Park (one near the sewage outfall and the remaining forming transects across a depth gradient with 4 inner, 4 mid and 4 outer), 6 in Cockburn Sound (5 forming a transect along an anthropogenic stress gradient at the northern end and 1 at the southern end), 2 localities between these regions at City Beach and Hall Bank, 1 within the Swan River and 7 at Jurien Bay to the north. At each site, physical factors of bottom water temperature, depth, water column light attenuation and the structure of sediment such as presence of ripples, depth of anaerobic sand and compactness were recorded. In addition, a water column integrated sample was collected and chlorophyll a quantified. Five transects of 5x1m were established at each site, ten 30mm diameter cores to 50mm depth and three 150mm diameter cores to 100mm depth were randomly collected within the transect, and all macrofauna collected using a small rake to search the sediment. Macrofauna were identified, counted and weighed. The small cores were sectioned into 0-2cm and 2-5cm depths and the size fractions from all 10 relating to 1 transect pooled and subsampled: one was analysed for organic carbon and nitrogen and a second for benthic microalgae biomass as chlorophyll a. One of the large cores was dry sieved through a set of 15 sieves from 0.063 to 8.0 mm pore size to determine proportions of grain size. One of the remaining cores was washed through 9 sieves from 8.0 to 0.5mm and biomass of infauna of each size class determined and daily secondary production calculated.