At Ningaloo Reef (21º50'S to 23º35'S), where the Leeuwin currnet is of particular note on the adjacent shelf, and at Scott reef (14 º04'S), which is under the influence of the Indonesian through flow, long term data exists in the respective shallow reef habitats, but until recently data has been virtually non existent in the majority of waters (>30 m) because of constraints on scientific diving depths. Recent deeper-water seabed surveys at Ningaloo Marine Park and Scott Reef including missions with the AUV Sirius in depths from 20-150m have demonstrated that in both areas extensive and diverse benthic habitats exist that contribute significantly to the known biodiversity values of the system.
The primary objective of this work was to describe biological assemblages associated with deep coral reef systems at Scott Reef in West Australia. A significant proportion of South Scott Reef and the adjacent lagoon lies in waters between 30 m to 70 m deep that support a range of habitats similar to many of the submerged shoal systems strung along the edge of the continental shelf in the Timor Sea. The South Scott Reef lagoon covers 300 km2 and is the largest area of this type observed on a single reef system in the NW region.
Understanding the nature and dynamics of these deeper water areas will not only better describe the true extent of Australia’s tropical reef resources, but will contribute to a broader understanding of the overall resilience of coral reefs in the NW region.
Scientific diving effort supporting a number of long term monitoring sites at Scott Reef is strongly biased towards depths of 20 m or less, with very few investigations on coral reefs venturing beyond 30 m. Remote sampling approaches are required to explore areas such as the deeper lagoon at Scott Reef. During the last decade a few surveys using simple towed video and small ROVs have begun to be used to survey the deeper South Scott Reef lagoon.
The initial habitat maps derived from these surveys suffer from the coarse interpolation used to join a limited number of survey points. The quality of the video used has also severely restricted the taxonomic resolution possible, precluding accurate assessment of species distributions and has provided limited information for monitoring purposes. In order to produce an accurate, high resolution habitat map of the deeper reef waters and to establish viable deep water monitoring sites, high resolution acoustic mapping using digital mulitbeam from Geosciences Australia was completed in parallel with collecting georeferenced seabed images using the AUV Sirius operated by the IMOS AUV Facility and the existing AIMS towed video with high resolution stills systems.
The first survey of the IMOS AUV Facility benthic observing program were undertaken at Scott Reef in 2009. These sites were revisited in 2011 and again in 2015. The 2015 campaign to Scott Reef was supported by the Schmidt Oceanographic Institution. The objectives of the work were to revisit benthic reference sites throughout the Scott Reef lagoon and to demonstrated coordinated deployment of multiple robotic assets.
We invited a number of international collaborators to join us, including the University of Sydney’s Australian Centre for Field Robotics, the University of Rhode Island (URI) Graduate School of Oceanography, the Woods Hole Oceanographic Institution (WHOI), the Massachusetts Institute of Technology (MIT) School of Aerospace, the University of Hawaii, Australian Marine Ecology (AME) and Evologics Gmbh the supplier of our acoustic tracking and communication systems.
In addition to repeating our IMOS AUV surveys, we were able to demonstrate the simultaneous deployment of multiple AUV systems, an Unmanned Surface Vessel and an Autonomous Glider equipped with novel acoustic navigation and obstacle avoidance systems. All operations were monitored from the support vessel throughout the 10 day cruise.
The deeper shelf areas of Ningaloo Marine Park have been revealed to contain highly diverse filter feeding communities located over relict geological features in depths from 30-90m. These sponge dominated habitats now provide an additional biodiversity attribute for the NMP, which will be factored into management of the park in the future and is to be considered for World Heritage listing (likely proposed Feb 2010). The growth, orientation and feeding of sponges in this region are likely closely coupled to coastal productivity and water movement, which is significantly modulated by the oceanography.
Marine scientists and engineers deployed the AUV Sirius to explore the ocean floor at Ningaloo in WA in 2007 and again in 2013. The joint expeditions between scientists from the Australian Institute of Marine Science (AIMS) and the University of Sydney's Australian Centre for Field Robotics (ACFR) was designed to explore the suitability of AUVs for environmental monitoring. In all, half a million images were collected on these dives, with the vehicle operating on the continental shelf in depths of 40-100m and within upper canyon areas in depths of up to 250m.
The individual stereo images, which are captured directly onto onboard computers, can be used to measure features of the seabed with unmatched clarity and detail. These images are being assembled together with sonar bathymetry into mosaics that enable larger scale patterns in the data to be observed. Stitched together the digital photos will effectively provide photographic maps of the seabed, giving an idea of the distribution of benthos in the survey areas.
For AIMS, this expedition has played a critical role in exploring the use of robots in underwater research. Robotic technology is a very effective way to run controlled surveys of steep walled canyons and other complex terrain. The vehicle uses a variety of sensors to navigate and to follow its planned mission. The data collected can then be geo-referenced to allow scientists to assess how deep sea communities are distributed as a function of depth or seabed composition.