DOI: 10.5061/dryad.mpg4f4r1s
title: Offshore platforms as novel ecosystems: a case study from Australia’s Northwest Shelf

description: The decommissioning of offshore oil and gas platforms typically involves
 removing some or all of the associated infrastructure and the consequent
 destruction of the associated marine ecosystem that has developed over
 decades. There is increasing evidence of the important ecological role
 played by offshore platforms. Concepts such as novel ecosystems allow
 stakeholders to consider the ecological role played by each platform in
 the decommissioning process. This study focused on the Wandoo field in
 Northwest Australia as a case study for the application of the novel
 ecosystem concept to the decommissioning of offshore platforms.
 Stereo-baited remote underwater video systems were used to assess the
 habitat composition and fish communities at Wandoo, as well as two control
 sites: a sandy one that resembled the Wandoo site pre-installation, and
 one characterised by a natural reef as a control for natural hard
 substrate and vertical relief. We found denser macrobenthos habitat at the
 Wandoo site than at either of the control sites, which we attributed to
 the exclusion of seabed trawling around the Wandoo infrastructure. We also
 found that the demersal and pelagic taxonomic assemblages at Wandoo more
 closely resemble those at a natural reef than those which would likely
 have been present pre-installation, but these assemblages are still unique
 in a regional context. The demersal assemblage is characterised by
 reef-associated species with higher diversity than those at the sand
 control and natural reef control sites, with the pelagic community
 characterised by species associated with oil platforms in other regions.
 These findings suggest that a novel ecosystem has emerged in the Wandoo
 field. It is likely that many of the novel qualities of this ecosystem
 would be lost under decommissioning scenarios that involve partial or
 complete removal. This study provides an example for classifying offshore
 platforms as novel ecosystems.
description: This dataset was collected using stereo-baited remote underwater
 video systems (Stereo-BRUVS). Seabed stereo-BRUVS consist of
 two GoPro cameras mounted 80 cm apart on a horizontal base bar, each
 converging at an angle of four degrees to a common focal point. A
 galvanised steel mesh bait cage containing 800 g of crushed pilchards is
 attached to the end of a 1.5 m long bait arm. Seabed stereo-BRUVS are
 deployed at least 200 m apart for a minimum of 60 minutes. Mid-water
 stereo-BRUVS consist of the same horizontal base bar as seabed
 stereo-BRUVS, mounted on a 1.45 m long steel upright to provide stability,
 and suspended 10 m below the surface. They are baited with 1 kg of crushed
 pilchards in a perforated bait canister on a 1.5 m long bait arm, which
 acts as a rudder to keep the cameras facing down-current for the duration
 of the deployment. Mid-water stereo-BRUVS are deployed for a minimum of
 120 minutes, and in this study, are anchored to prevent entanglement with
 subsea infrastructure. Video processing commenced either
 once seabed stereo-BRUVS had settled on the seabed, for a period of 60
 minutes, or when the mid-water stereo-BRUVS had stabilised at 10 m depth
 following deployment, for a period of 120 minutes. All animals entering
 the field of view were identified to the lowest possible taxonomic level,
 and abundance was estimated using the conservative abundance metric MaxN,
 which is the maximum number of individuals of a given taxon in a single
 frame (Cappo et al. 2006). The appropriate length metric (e.g. fork length
 FL, disc width DW, or carapace length CL) was measured in stereo with
 individuals measured where they were well positioned relative to the
 camera and not occluded by other individuals. For seabed stereo-BRUVS, the
 habitat visible in the field of view was broadly categorised into three
 groups: sand (bare substrate with no visible macrobenthos or other marine
 growth); sparse macrobenthos (predominantly bare substrate with less than
 50% biotic cover); and dense macrobenthos (the visible substrate was
 dominated by more than 50% biotic cover).
description: Usage notes can be found in the file titled "Stereo-BRUVS
 data usage".