AUV-assisted Surveying of Relic Reef Sites Along the GBR Margin
The AUV was part of a three week research cruise in September, 2007 aboard the R/V Southern Surveyor documenting drowned shelf edge reefs at multiple sites in four areas along the Great Barrier Reef. This collaborative cruise included scientists from the University of Sydney, James Cook Univesity, CSIRO, Oxford, the University of Edinburgh and Fugro Seafloor Survey. We were able to document relic reefs up to 20k years old formed during previous ice ages when sea leves were up to 100m lower than today. The study of these structures may yield insights regarding potential future sea level changes and their potential impact on sensitive reef areas such as the GBR.
Four sites along the extent of the Great Barrier Reef were selected for detailed bathymetric mapping, AUV seafloor imaging, dredging and grab sampling to determine substrate composition during the R/V Southern Surveyor cruise SS07/2007. Over the course of the three week voyage the AUV was deployed at a dozen locations undertaking both overlapping grid surveys of particular features as well as cross shelf transects to document the variability in benthic habitats at varying depths.
The vehicle's role was in validating the seafloor characteristics of significant features observed in the large-scale bathymetric and sub-bottom profiling data. The high spatial resolution and capacity to geo-reference the resulting imagery provides an invaluable mechanism for observing the extent and composition of particular benthic habitats. Unlike dredging, the AUV survey data maintains the spatial relationships of observed seafloor features of interest. Furthermore, sampling using dredging may introduce bias towards things that actually break off when a tow sled is dragged along the sea floor. The AUV imagery on the other hand provides an image of everything within the field of view of its camera that can then be analyzed to describe the composition of taxa within the survey area.
The AUV imagery shows a variety of of benthic communities and substrates that include red algae-encrusted fossil rock, thriving hard and soft coral, gorgonians (sea whip or fan) and sponge communities and Halimeda (green algae). Post-cruise analysis of the AUV and multibeam data is currently being used to derive quantitative information about the distribution of benthic communities and habitats.