Offshore platforms as novel ecosystems: A case study from Australia’s Northwest Shelf

Abstract

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 characterized 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 characterized by reef‐associated species with higher diversity than those at the sand control and natural reef control sites, with the pelagic community characterized 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.

To What Extent Can Decommissioning Options for Marine Artificial Structures Move Us Toward Environmental Targets?

“…For instance, maintenance of connectivity as a result of introducing hard bottom species/habitats into sedimentary environments (van der Molen et al, 2018;Tidbury et al, 2020), can underpin stability in ecological networks (Melià et al, 2016;Clubley et al, 2023), structure biodiversity across geographic space (Cristiani et al, 2021), and ensure genetic diversity, population development and growth across multiple spatial scales (Baguette et al, 2013;Hogan et al, Ross et al, 2017). Given global rates of habitat loss and fragmentation and degradation of habitats (Reddin et al, 2022), either the maintenance or addition of 'novel' habitat as a result of MAS could support biodiversity conservation efforts (Ben-Hamadou et al, 2023;van Elden et al, 2022). Indeed, developers are asked to not only consider mitigation measures but also compensation measures, such as recreating habitat to accommodate lost ecological structure and functions.…”