The Benefits of Leaving Oil and Gas Rigs Intact to Serve as Artificial Reefs a report by Steve Kolian EcoRigs Non-Profit Corporation
Offshore platforms stand out from all other artificial reefs because they occupy the entire water column, from the sea floor through the splash zone, whereas conventional artificial reefs usually only occupy 10 to 40 percent of the water column. When platforms are toppled over to create artificial reefs, 90 % of fish and invertebrate populations either perish or leave the structure. When rigs are left standing the fish biomass is ten times greater, per unit area, than the fish biomass at the Flower Gardens Fish Sanctuary.1
The Gulf of Mexico is home to 4,000
artificial reefs that are ten times bigger, ten times stronger, and ten times more prolific than average artificial reefs. They create one of the most prolific ecosystems on the planet.
They clearly produce fish rather than merely attract fish. At petroleum platforms, shallow-water fish, mid-water fish and deep-water fish are all found in the same place. One platform can produce 10,000 to 30,000 adult fish2
(Stanley and Wilson 2000) and millions of invertebrates3–6
murky seafloor absent of natural reef recruiting grounds. The platform obligatory reef fish communities consist of colorful Caribbean obligatory reef fish such as angelfish (sp. Pomacanthidae), surgeonfishes (sp. Acanthuridae) damselfish (sp. Pomacentridae), wrasses (
sp.Labridae), filefish (sp. Monacanthidae), spadefish (sp. Ephppidae), triggerfish (sp. Balistidae), and butterfly fish (sp. Chaetodontidae).
How Did They Get There? in an
The invertebrate community at platforms is even more diverse than the fish community. Most of the organisms exhibit a preference for the upper 30 m of the water column beneath a platform.8,3,5,6
and abundance of invertebrates drops significantly below 30 m and often when a platform is toppled over and ‘reefed’, most of the invertebrates perish when they are re-oriented in the water column.
The Attraction versus Production Debate Whether artificial reefs attract fish or produce fish is a topic that fisheries managers have debated for the last 40 years. Contributing to this long running disagreement is the fact that artificial reefs attract and produce fish. Only a handful of scientists have viewed firsthand the marine life at the offshore platforms and less than 4 % of the 4,000 structures in the Gulf have been studied. Many platforms clearly produce thousands of obligatory reef fish and more importantly, a diverse invertebrate coral reef community. Obligatory reef fish are the type of wide bodied Caribbean reef fish presented in Figure 1. Once the platforms are toppled to create an artificial reef, they are not as productive and they tend to produce and/or attract only facilitative reef fish such as snapper1 (sp. Lutjanidae), grouper (sp. Epinephelinae) and jacks (sp. Carangidae).1
Investigations into the attraction and production usually focuses on one fish, such as red snapper (Lutjanus campechanus) and fails to recognize the large populations of shallow water, reef dependent fish that are living in an area defined by thousands of square miles of
© TOUCH BRIEFINGS 2011
Federal policy makers, non-governmental agencies (NGOs), and many marine scientists use the attraction hypothesis to dismiss the ecological value of the platforms despite the numerous peer review publications that point out the contradictions of the attraction versus production model.9–13
area about half the size of a football field. The deck, 20 m above the water, casts a shadow during the day that fish use to hide from predators; at night the operational lights create a ‘halo’ of light in the water below that attracts photophillic plankton and the small bait fish that feed on them.7
The diversity
Obligatory reef fish employ two types of reproduction; they deposit eggs in nests or they broadcast their spawn in the current. Fertilised larvae drift for weeks and sometimes months. If they are lucky they encounter suitable coral reef habitat where they metamorphose into post-larval fish. The platforms act as surrogate nesting grounds for broadcast spawning larval fish as seen in Figure 2, a juvenile angelfish that probably arrived to the platform in a larval state where it then metamorphose into a juvenile fish.
How Do The Egg-laying Fish Get There?
Several species of juvenile and adult egg-laying fish are found in large populations, exceeding several thousand individuals, at platforms that are great distances (50–100 km) from natural coral reef recruiting grounds. The fish could be leap-frogging from one platform to the next, taking their chances traveling over miles of open water or murky seafloor. This is possible but unlikely because the wide-bodied reef fish are vulnerable to predation in open water. Another theory is that these fish are ‘blown-in’ from the tropics during hurricanes; again, possible but not likely. The most plausible explanation is that the juvenile fish hitch a ride to the platforms on floating seaweed called sargassum. Large mats of sargassum drift into the Gulf of Mexico from the Sargasso Sea, carrying with them a cargo of juvenile fish from the tropics. Large ribbons of sargassum float across the Gulf of Mexico and when they pass by a platform, the juvenile reef dependent fish jump ship for a better life on the living coral reef growing on the pilings. This phenomenon was observed in action by Quenton Dokken (2010)14
who reported that a cloud of juvenile fish raced from the sargassum to the safety of a platform as the floating sargassum passed by the structure in the current.
Steve Kolian received his graduate degree in Environmental Science from Tulane University. He participated in a progressive marine aquaculture project as a research scientist at Louisiana Marine Consortium (LUMCON) and has consulted for the offshore oil and gas industry. Mr Kolian has researched the utilisation of retired platforms for 20 years and has established himself as the preeminent leader in the effort to utilise expired structures for alternate purposes. Mr Kolian
was instrumental in the drafting Section 388 of the Energy Policy Act (EPAct) of 2005 (Public Law [PL] 109-58) which authorises the use of Outer Continental Shelf (OCS) facilities (offshore platforms) for alternate uses.
E:
stevekolian@hotmail.com
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Engineering & Construction
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