The dynamics of the seasonal evolution of chlorophyll a at the continental shelf break around 32 degrees south has been investigated using a one-dimensional numerical BGC model at shelf and lagoon scales. The results show that a combination of vertical mixing associated with the Leeuwin Current and surface cooling during the winter months is responsible for the wintertime increase in chlorophyll a concentration at the shelf break (Greenwood and Soetaert, 2008). In addition, variation in the timing and magnitude of the winter increase in chlorophyll is shown, for the first time, to relate to the strength of the Leeuwin Current. A nitrogen budget for the southwest WA shelf has been derived by diagnosing the simulated fluxes of particulate and dissolved nitrogen from the 3-D model across the shelf boundaries (across two cross-shelf transects at 27S and 34.5S and across the 100 m isobath) as well as deposition and release of nitrogen at the seafloor.

The Science Plan for WAMSI Node 1 Project 1 characterised the south west Australian marine coastal and shelf ecosystem structure and function. Mooring progam An array of instruments was deployed four times between July2007 and May 2008, recovered after 4-6 weeks each time to download data, and service the instruments. CTD Surveys During the course of the mooring program a ctd survey of the region was completed at approximately monthly intervals using the RV Linnaeus. In the first 2 surveys a grid of 25 stations was occupied after which a further 5 stations were added to the northern end of the grid.

Within this experiment the blue mussel ( Mytilus edulis ) is being used as a proxy indicator to understand rates of secondary production across the continental shelf off Marmion WA. The experiment is being run at 5m depth intervals between 0 and 40 meters. Length and width of valves and wet/dry weights of tissue matter are being measured to compare condition and growth rates of individuals from different depths. Stable isotope values are obtained to compare relative C13 and N15 values, to understand if there is a difference in diet across the shelf. Water sampling is also being carried out and regular intervals whilst the experiment is deployed to investigate differences in Particulate organic matter, Chl-a, HPLC and isotope values of organic matter in the water column, to aid in explaining variation in growth and diet patterns.

A) Rates of primary productivity for reef macroalgal and sediment microalgal communities will be determined from measurements of oxygen release (and/or CO2 consumption) collected from reef (3x) and bare sand/microphytobenthos (3x) communities using benthic chamber incubations. B) Nutrient enrichment experiments - response of macroalgae will be measured in terms of N assimilation in algal tissue, changes to species composition and changes in abundances. The response of consumers (abundance and other aspects of population dynamics, biomass, feeding biology and fecundity) will also be investigated, using video for mobile (fish) grazers, and quadrat sampling for less mobile grazers (eg. gastropods on reefs, urchins in sediments). Variations in the isotopic composition of the algae and consumers will be used to assess nutrient exposure and subsequent energy flow pathways into secondary production.

Despite the apparent importance of microphytobenthos and macroalgal populations as primary producers, primary productivity data and particularly data investigating the controls on primary productivity in WA shelf waters are sparse. We have investigated microphytobenthoc and macroalgal primary productivity in Marmion Lagoon by measuring oxygen evolution during a number of targeted incubations.

Hydrodynamic and wave modelling to simulate currents and wave action over reef and lagoon systems.

In May-June 2007, an "autumn bloom cruise" was conducted on the National Marine Facility, Southern Surveyor, led by Peter Thompson. The voyage was conducted in three legs, with a the first conducted from May 10th to May 15th focused on benthic habitats. Benthic based operations were performed over two transects near Perth at 31.71ºS and 31.76ºS from 115.63ºE to 115.15ºE with stations at depths of 30, 40, 50, 75, 100 and 150m. Acoustic swath mapping of the sea-bed was conducted during the entire voyage; at each of the 12 study sites, benthic sled dredges, sediment grabs, benthic video and CTD casts were completed.

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.

We attempted to asses the potential for using stable isotopes as a tool for rapid assessment of trophic interactions in a nearshore benthic ecosystem in Western Australia. The information gained from this experiment will help us to refine our use of stable isotopes, and contribute to efforts to develop "sharper" tools to achieve the ultimate goal of providing accurate characterisation of food webs, information sorely needed by managers of marine resources. A controlled laboratory scale feeding experiment with the gastropod, Turbo torquatus was conducted to assess the suitability of stable isotope analyses for diet inference. Seventy eight T.torquatus were fed enriched macroalgae (Ulva lactuca) to alter their natural isotopic profile (ä13C and ä15N) and then fed three locally occurring macroalgae (Ulva lactuca, Carpopeltis phyllophora, and Ecklonia radiate) over 17 weeks to assess how their isotopic profile reflected that of their diet. Feeding the enriched macroalgae (Ulva lactuca) to Turbo torquatus increased their carbon and nitrogen isotope ratios to very high levels after just 72 hours. Unfortunately even after 17 weeks of feeding on natural macroalgae (not enriched) the heavier isotope for both carbon and nitrogen was still retained in the muscle tissue of the gastropods. This suggests that the enrichment of Ulva lactuca appears to have been for too long or the concentration of 98% ä13C NaHCO3 and 98% ä15N NH4Cl was much too high.

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.