A Review of the Ecological Performance and Habitat Value of Standing versus Reefed Oil and Gas Platform Habitats in the Gulf of Mexico

In the northern Gulf of Mexico (GOM), approximately 1,800 oil and gas production platforms (hereafter “standing platforms”) function as de facto artificial reefs. As a large number of platforms are reaching the end of their production lifespans, some of these structures will be converted to permanent artificial reefs via state Rigs-to-Reefs (RTR) programs (many others have already been “reefed”), which involve partial removal or toppling of the platforms (hereafter “reefed platforms”) either in place or moved to alternate approved locations. The conversion of standing platforms into artificial reefs results in a structure with a lower vertical relief, and no physical connection to the upper water column. As decommissioned standing platforms are increasingly converted into artificial reefs, it is important to evaluate the ecological effects of this physical transformation on platform-associated communities. Furthermore, the number of standing platforms in the northern GOM continues to rapidly decline as removals through the decommissioning process exceed new installations. Thus, there is a central need for science-based decision making on the proper use of these structures and to establish the best management practices to maximize RTR programmatic goals. Here, we review the current state of scientific knowledge comparing the ecological function and habitat value of standing and reefed platforms in the northern GOM and identify critical information gaps in need of future research with special emphasis on the ecological functionality of standing platforms and performance related to upper-water column benefits. Allowing platforms to remain standing would ameliorate the loss of biodiversity and fish biomass due to the loss of shallow water substrate. While the ~85-ft (26-m) clearance guidelines observed in current RTR practices reduce some aspects of biodiversity (e.g., upper water column species) associated with standing platforms; nevertheless, there is evidence to suggest that partially removed platforms do continue to provide an effective means of preserving the community structure and ecological functions associated with standing platforms, particularly for economically important species. Furthermore, reefed platforms retain the majority of the fish community in the lower depth strata, including species that are targeted by recreational and commercial fisheries. As a result, studies evaluating how standing and reefed platforms function to support fish populations in the GOM have primarily focused on the biological characteristics of the economically important red snapper (Lutjanus campechanus) given this species iconic status and importance as the most valuable reef fish in the GOM. As a demersal species, both standing and reefed platforms appear to provide suitable habitat with sufficient resources to support its biological needs. Though, the lack of similar trends among artificial and natural habitats in the northwestern and north-central GOM highlights the complex nature of habitat- and region-specific contributions to the GOM red snapper stock and warrants further investigation, especially into the loss of structure and function of habitat as well as los of species in the upper water column. Nevertheless, increased emphasis on a wider range of species, including other broadly distributed fisheries species of commercial and/or recreational value (e.g., greater amberjack, Seriola dumerili), and on whole-community and functional approaches will build towards a more mechanistic understanding of the broader ecosystem values provided by both standing and reefed platforms. The extensive variability in marine life and environmental conditions such as water depth, distance from shore, size, and many other characteristics associated with existing standing platforms makes it difficult to establish a generic set of predictions regarding the ecological consequences of 2 different decommissioning alternatives. Hence, decisions should be made on a case-by-case basis using all available scientific information. As standing platforms in the GOM reach the end of their productive lives at an increasing rate, long-term monitoring studies are critically needed to empirically assess changes to community structure and functionality prior to and following reefing or complete removal. These studies will ensure that RTR programs are operating at maximum efficiency and performance as it relates to reefing goals, and facilitate data-driven decisions to determine which standing platforms would be most economically and ecologically viable to remain standing and/or converted to artificial reefs. In summary, this comprehensive literature review identified several key findings comparing the ecological function and habitat value of standing and reefed platforms in the GOM: • Allowing platforms to remain standing would ameliorate the decline in biodiversity and fish biomass due to the loss of shallow water (<26 m) substrate. • Reefed platforms, especially partially removed platforms, continue to provide an effective means of preserving the community structure and ecological functions associated with standing platforms, particularly for economically important species. Thus, even some structure retained is highly valuable. • At this time, the ecological consequences of different decommissioning alternatives and decisions should be made on a case-by-case basis by the platform owner in conjunction with resource managers until a scientifically informed set of predictions can be formulated based on short- and long-term monitoring studies. • Future research, including long-term monitoring studies and increased emphasis on a wider range of species, is critically needed to fully understand the impact of decommissioning standing platforms and different reef configurations on the ecology and productivity of the GOM.