| Location: | Orca field, offshore Venezuela |
| Position: | 9° 44' 07" N 59° 44' 60" W |
| Depth: | 543m |
| Water Temperature: | No data |
| Dates: | 25 July - 02 August 2007 |
| Industry Partners | |
| Gas & Oil Company | Statoil |
| ROV Operator: | Subsea7 |
| Rig operator: | Transocean |
| SERPENT Representatives: | Dr. Daniel Jones |
Mission Plan
This report summarises the SERPENT work carried out at the Orca field in July/August 2007. The main aims of this work have been to familiarise the different partners with the project practicalities as well as to start to generate some scientific and environmental data from the survey area.
The background knowledge of the deep-sea communities of offshore Venezuela is extremely limited. Some of the specific aims of this program include increasing our understanding of the impact related disturbances and how to improve their management. Specifically we aimed to investigate variation in biological communities and some of the environmental controls in relation to drilling operations.
Data collection and analysis
The Orca field, in the Orinoco fan, is an area heavily influenced by sedimentation from the Orinoco river, one of the longest in South America . Knowledge of the biology of offshore Venezuela extremely poor, essentially limited to SCUBA diving depths (around 30 m), with absolutely no biological investigations of the entire bathyal region (depths of 200 to 2000 m) until now. Working in collaboration with the Universidad Simón Bolívar in Caracas, SERPENT scientists used a Subsea 7 Centurion ROV to explore the diversity and density of the seabed communities at Orca and to find out the effects of exploratory drilling on this relatively pristine ecosystem.
This first dive at Orca revealed a range of unusual, often colourful animal life including abundant solitary corals, large, flowerlike tube anemones and the ancient stalked crinoid, once incredibly abundant, now only found in the deep oceans of the world. A range of strange fish were seen including a flattened, bright-orange anglerfish and an as yet unidentified fish with modified fin rays splayed out around its head presumably to sense its surroundings in this perpetually dark environment. An ROV-operated scoop was used like a butterfly net to catch these denizens of the deep and bring them to the surface for detailed microscopic investigation. We also deployed a series of traps, designed to catch the common scavenging fauna. These animals rapidly take advantage of large food falls to the deep, often gorging themselves until they cannot move. A tuna bait was particularly effective catching the slimey hagfish – who can produce several litres of slime an hour, and most excitingly a giant isopod. This creature is very closely related to the common woodlouse but has undergone, in evolution, a process of gigantism in response to limited food availability in the deep-sea - they have been observed at lengths of nearly half a metre! These specimens will form the basis of a deep-sea collection of preserved fauna for future work by Dr David Bone and Dr Juan Cruz at Universidad Simón Bolívar.
A Bathynomus sp. giant isopod collected from the seabed
The impact of initial, or tophole, drilling is usually visible on the seafloor as a build-up of sediment on the seabed surface. At this site, no chemicals were used to drill this section of the well so we could investigate the effects of initial sedimentation on the seabed community. The drilling activity provides a useful experimental treatment which can be used as a proxy for the effects of natural sedimentation from down-slope transportation of fluvial sediments common in the area. This process is extremely poorly understood as a result of difficulties in experimentation, especially at a suitably large-scale in deep-waters. Initial results suggest motile fauna quickly recolonise disturbed areas, not being impaired by new sediments, and many of the sessile fauna showed adaptations for clearing sediment effectively from their feeding surfaces. We hope to assess the communities again, as part of a Statoil sponsored monitoring programme, after drilling to quantify recovery in the area.
An anemone on the seabed
a Cerianthid sp. anemone
An unidentified jelly
For further information please contact:
Dr Daniel Jones , SERPENT Project, National Oceanography Centre, Southampton, UK
