Between Dec 06 and Feb 07 the number and size (estimated maximum diametre cm) of sessile invertebrates (sponges, corals) were recorded across 14 different habitat types within Marmion lagoon. 16 sites within 4 locations (inshore, inner-mid, outer-mid, offshore)were surveyed using 1 x 25m UVC belt transects. Survey data has been used to investigate the abundances of potentially important fauna across differeing habitat types and have confirmed that patch structure is an important and ubiquitous characteristic of Marmion Lagoon benthic communities, with strong implications for biodiversity and productivity.

During November 2007 three study sites were established that form the basis of repeated observations of natural temporal variability in habitat patch dynamics. The sites are located on reefs in the Marmion Marine Park with each site approximately 2500 m2 in extent. The sites are comprised of a patchy mosaic of kelp forest, mixed algal canopy, and low foliose algal assemblages. At each site nine circular areas measuring 3m in diametre have been cleared of all algae and changes in percent cover of algae monitored over an 18 month period using photo quadrats (0.25m2). The successional process observed within circular clearances have been used to help understand the causal mechanisms underlying patch formation and maintenance at Marmion Reef.

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.

The study focused on locations in Marmion Lagoon in south-western Australia (31º49.4 S, 115º02.5 E) Five nearshore reefs: South Lumps, Whitfords Rock, The Lumps, Cow Rock and Wreck Rock (Table 1) were sampled. All sites were sampled in summer and autumn (January 2007 to April 2008) during calm conditions. Sponges and ascidians at each site were chosen haphazardly. Organisms on top of the reefs and reef walls were sampled and filtration rates measured.