ABSTRACT. Coastal reef communities dominated by zooxanthellate alcyonacean octocorals extract large quantities of suspended particulate matter (SPM) from the water column. Concentrations of SPM in water parcels, tracked by a curtain drogue, were measured before and after passing over 2 strips of soft coral dominated, near-shore reefs -200 m long, and over 2 adjacent sand-dominated strips for comparison. The reefs were covered with 50% zooxanthellate octocorals (total standing stock: -270 g AFDW m-'; mean live tissue volume: 70 1 m-2), 7 % hard corals, 15 % turf algae with bioeroding sponges underneath, and < l % other filter feeders (sponges, tunicates, and bivalves). Downstream of the reef communities, chlorophyll, particulate organic carbon and particulate phosphorus were significantly depleted. The depletion of chlorophyll averaged 35 % of the standing stock, whereas the net depletion of particulate organic carbon and particulate phosphorus was 15 and 23 %, respectively. Rates of depletion were simllar for the 2 reef sites and 3 sampling periods, and were independent of upstream particle concentration. In contrast, concentrations of particulate nitrogen and phaeopigments were similar before and after passage across the reef sites. On the sandy sites, downstream concentrations of particulate nutrients, chlorophyll and phaeopigments were all similar to upstream concentrations. The net import of particulate organic carbon into the reef was estimated as 2.5 * 1.1 g C m-' d-'. Less than 20% of this carbon Import could be explained by area-specific rates of removal by sponges, tunicates, bivalves, and hard corals, suggesting that soft corals were the pnmary sink of carbon. The data suggest that detritus and other small SPM ( < l 0 pm particle size) are an important food source for alcyoniiddominated reef communities in high turbidity regimes.

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The use of digital echosounders with post-processing commercial seabed classification software is becoming increasingly popular to create high-resolution resource maps of marine habitats over large scales. Here, we examine the Biosonics Visual Bottom Typing (VBT) seabed classification software (version 1.91). Although the VBT software uses potentially robust seabed classification parameters and has many useful features, a major drawback of the software is that it does not normalize echoes to a reference depth (typically the average survey depth). Depth normalizing adjusts for a change in echo length with depth. Without it, the VBT classification parameters that are calculated from the energy integral of the returned echo envelope over a fixed sampling window can be depth biased. The degree of misclassification from depth biasing will depend on the particular echosounder specifications (beamwidth (at −3dB) and pulse length) and characteristics of the survey area (depth variation and bottom acoustic diversity). Depth normalization applied before classification parameters are calculated is a very simple solution to potential depth-related misclassification and should be incorporated into the VBT software as a matter of priority to ensure its reliability and broad user application.

Australia’s marine economy is worth over $70 billion a year, of which offshore oil and gas is a big contributor. Operating safely and in an environmentally sustainable way is vital to the long-term success of Australia’s offshore petroleum sector. Making good risk management decisions depends on a sound understanding of the complex marine environments in which they operate. Key emerging challenges include the effects of noise on marine life, decommissioning of offshore infrastructure, and the unprecedented rate of change in natural marine systems. The Australian Institute of Marine Science (AIMS) undertakes research that helps industry, regulators, government and the wider community to make informed decisions about the management of Australia’s marine estate. Working closely with industry and government partners, AIMS has established some of the world’s longest running and most comprehensive tropical marine monitoring programs. The regional baseline datasets span the subtropics of Western Australia, the North West and North Marine Regions, through to the Great Barrier Reef and the Coral Sea Marine Region. This unique repository of data and environmental intelligence allows quantification of system changes, modelling of anticipated future trends and impacts of development, and the development and testing of risk mitigation measures. Examples of research specifically tailored to meet the needs of the offshore oil and gas industry include recent projects in noise management, eco-toxicity and machine learning/automation. In each case, AIMS and its science partners worked with industry to develop research programs designed to help manage specific risks, or conduct work more efficiently and safely.