|Location:||Ocean Bounty, Mutineer Subsea Field Development|
|Position:|| Northwest coast offshore Australia
19º 15’ 33.7” S
116° 38’ 16.435” E
|Water Temperature:||No data|
|Dates:||20 - 27 August 2006|
|Gas & Oil Company||Santos|
Mr Gareth Andrews, University of Sydney (Contact through Dr Adele Pile)
The science goals for this project are to conduct baseline environmental surveys, using detailed ROV megafaunal video transect surveys to provide quantitative data on megafaunal ecology; particularly abundance, diversity and distribution in this area. This mission will focus on determining the nutritional ecology of this location, in particular, the nutrient selection behaviour of the deep-sea benthic megafauna. This mission also aims to look at the impact anthropogenic disturbance events have on deep-sea communities.
A highly successful mission resulted after 8 days of ROV operations. Four 40 m video transects were completed, for megafaunal abundance, diversity and distribution in the area. Transects were conducted at 210°, 180°, 160° and 140° from the BOP. Videos will be analysed for megafaunal diversity and habitat mapping. This is a soft bottom environment in 150m water depth. Large aggregations of sea urchins were discovered on this mission, along with anemones and encrusting sponges on the existing sub-sea sturctures, consistent with soft bottom communities. Baited traps were deployed within and outside of the drill spoil as on previous missions to other sites. This mission however, there was no scavenger activity or tracks within or around traps.
Food choice arrays were also deployed on this mission, to monitor feeding behaviour of benthic scavengers and to determine if there is any dietary preference of these scavengers. Arrays consisted of six agar blocks: a natural and artificial protein source, a natural and artificial carbohydrate source, a natural lipid source, and agar as a control. Feeding plates were deployed on the open seabed as well as in caged experiments. Twenty three food choice arrays were deployed over 8 days, at randomly chosen compass headings, all approximately 40 m from the rig location. The feeding choice arrays indeed attracted urchins to the feeding plates which were videoed throughout the ROV dives. The arrays were retrieved and visual estimates of the amounts eaten recorded.
Nutrient selection behaviour of the sea urchin Diadema sp. was monitored, and urchins showed a clear preference for high-protein food blocks (squid-based). In caged experiments, a shift in preference from protein to kelp and seagrass was apparent. This suggests that Diadema sp. were protein deprived and were seeking to redress a nutrient imbalance by increasing their intake of protein. Having redressed this nutrient imbalance they returned to a high-carbohydrate, algae and plant-based diet. Analysis of video footage of urchin interaction indicates one urchin feeding will prevent others from mounting the feeding plates within reach of other urchins' spines. Feeding marks on the agar blocks once brought to the surface indicated which arrays were being eaten. Sea urchins were also evident adjacent to the BOP. They were obviously not deterred by drill spoil.
Sea urchins collected were dissected and the guts, gonads and Aristotle's Lanterns frozen for stable isotope analysis. Measurements of urchin tests and gonads were also taken. Urchins were found to have brittle stars on top of them, their legs following the exact pentaradial lines of the urchins.
We hope to return to Mutineer-Exeter in 2007 for repeated sampling.
We will conduct the same habitat mapping and bait trap experiments at other drill sites. This will allow us to compare biodiversity and processes between the locations. We will prepare a report for Santos after analysis of all the data. This research will contribute to the honours thesis of Gareth Andrews at the University of Sydney. We expect to publish these results in leading peer reviewed journals such as Marine Ecology Progress Series or Deep Sea Research in the near future.
For further information please contact:
Dr Adele Pile, SERPENT Project, Australia Region, University of Sydney. firstname.lastname@example.org
Thanks as always to our valued project partners