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Ecology

New housing options in unlikely places: Animals and oil platforms.

Claisse, J. T., Pondella, D. J., Love, M., Zahn, L. A., Williams, C. M., Williams, J. P., & Bull, A. S. (2014). Oil platforms off California are among the most productive marine fish habitats globally. Proceedings of the National Academy of Sciences (PNAS), 111(43), 15462 – 15467. doi:10.1073/pnas.1411477111

 

Background

Oil and gas production peppers our coastal waters with large metal structures, called rigs or platforms, which are used by

Figure one: Platform diagram and map of the study area. The platform midwater habitat encompasses the hard substrate of the platform structure from the water surface to 2 m above the seafloor, whereas the platform base habitat is the bottom 2 m of the platform structure. The platform structure consists of outer vertical pilings and horizontal crossbeams (i.e., the platform jacket) and the vertical oil and gas conductors in the center. Note this is a general display diagram and the designs of these structures vary from platform to platform. The 16 platforms (filled circles; names in all capital letters) and seven natural reefs (open circles) used in the study were surveyed for at least 5 (up to 15) y between 1995 and 2011.

Figure one: Platform diagram and map of the study area. . The 16 platforms (filled circles; names in all capital letters) and seven natural reefs (open circles) used in the study were surveyed for at least 5 (up to 15) y between 1995 and 2011.

the industry for a finite amount of time. Over the coming decades thousands of these existing structures will become economically unviable and decisions will need to be made about their removal. The situation may not be entirely bad though. New research has found that oil and gas platforms can act as new real estate for marine animals looking for a new home.

Oil and gas platforms can serve as artificial reefs due to the increased abundance of marine life living in and around them. Decommissioned rigs can be considered for a “rigs-to-reefs” approach involving leaving part, if not all, of the platform in the ocean indefinitely. The incentive is to promote the population growth of key species, particularly ones that are commercially valuable or in decline.

This study focused on oil and gas platforms off the coast of California and aims to answer the question of just how productive these environments can be.

 

Methods

The authors conducted biomass surveys annually using submersibles. The researchers counted, identified and estimated the length of all fish seen within two meters of the rig. Surveys were conducted off the coast of California at 16 platforms and seven natural reefs. Each location was surveyed for at least five years.

The oil platforms were measured at two levels: midwater habitats (surface down to 2 m above seafloor) and base habitats. The natural reefs were primarily rocky habitats. The researchers traveled from the surface to seafloor in research submarines to conduct visual surveys of each area. Annual densities (fish per square meter) were calculated for each of the three zones.

 

Results

 

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Table one: Estimates of fish biomass and production from various studies.

Oil and gas platforms off California have the highest fish biomass production per meter squared of seafloor than any marine habitat previously studied. Significantly greater total biomass production was seen at the platform base habitat than at natural reefs or midwater habitats.

 

Figure Two: Annual Total Production. (A) Annual production values scaled to per square meter of habitat for natural reefs (n = 56) and platform habitat subtypes [base (n = 111), midwater (n = 132)]. (B) Annual production values scaled to per square meter of seafloor for natural reefs (n = 56) and complete platforms (n = 111). Circles indicate individual data points and are jittered for visibility. Horizontal lines show the backtransformed estimated marginal means. The shaded box represents the 95% confidence intervals (CIs) of the mean. Differences were considered significant if the 95% CIs of their marginal means did not overlap.

Figure Two: Annual Total Production. (A) Annual production values scaled to per square meter of habitat for natural reefs (n = 56) and platform habitat subtypes [base (n = 111), midwater (n = 132)]. (B) Annual production values scaled to per square meter of seafloor for natural reefs (n = 56) and complete platforms (n = 111). The shaded box represents the 95% confidence intervals (CIs) of the mean. Differences were considered significant if the 95% CIs of their marginal means did not overlap.

 

 

 

 

 

 

Rig structures act as nurseries for small, juvenile fish and host a wide variety of invertebrates that are an important component of the food web in the areas studied. A platform offers a large amount of surface area compared to open water environments and many animals take advantage of this new real estate.

 

Significance

The rig environments were productive in this study because they offered suitable habitats in places that are otherwise devoid of natural habitats.

Human activities in the ocean generally are generally destructive to both fish and invertebrate marine species. Potentially destructive activities, such as oil and gas production, may have inadvertently helped to create new, highly productive habitats, particularly after the rigs are not in commercial use.

Further studies of oil rigs or wind and wave energy platforms could give new insights into the best infrastructure for supporting a healthy marine ecosystem. New platforms should be designed with conservation and long-term planning in mind.

Sarah Giltz
I am a doctoral candidate in Ecology and Evolutionary Biology at Tulane University. My research focuses on the larval dispersal and development of the blue crab in the Gulf of Mexico.

When not concerning myself with the plight of tiny crustaceans I can be found enjoying life in New Orleans with all the costumes, food, and music that entails.

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