Oil and gas platforms are producing 25-30 species of
These offshore platforms clearly produce fish rather than merely attract fish. Once the platforms are removed, the populations of invertebrates will die immediately and the obligatory reef fish will be lost to the biota if they survive the process of mandatory removal. Every year for the next 40 years, 100-120 platforms will be removed annually. Offshore of California, Dr. Milton Love is finding that platforms are creating excellent nursery habitat for several species of protected rockfish. Hundreds of thousands of rockfish are found at some platforms from post-larval stages to trophy size individuals. See underwater video of California platforms.
Attraction vs. Production Discussion
Whether artificial reefs attract fish or produce fish is a debate that U.S. fishery managers have not been able to settle over the last 30 years. Deliberations are divided into three sectors: attraction, production, and a middle ground that believes artificial reefs both produce and attract fish. In most cases, the latter is the most accurate description. Natural reefs and artificial reefs both attract and produce fish although some reefs tend to produce and some tend to attract fish. Oil and gas platforms are entirely responsible for producing 25-30 species of Caribbean reef fish on an anoxic continental shelf.
Production depends on the design, placement, and size of the artificial reef. Demersal (wide body) fish tend to be produced by the artificial reefs and pelagic (torpedo shaped) fish tend to be attracted to them. Bonsack 1989 suggested that artificial reefs fall along a gradient of production and attraction and discussed 5 biological events that would indicate whether artificial reefs are producing fish opposed to attracting fish. Artificial reefs are said to produce fish if they (1) provide additional food, (2) increase feeding efficiency, (3) provide shelter from predation, (4) provide new habitat for settling individuals that would otherwise have been lost to the population, and (5) indirectly, because fishes moving to artificial reefs create vacated space in the natural environment that allows replacement from outside the system. Also, increased production occurs when artificial reefs are placed in areas absent of natural reefs and designed for reef dependent species (Bohnsack 1989). Japanese artificial reef researchers regard the availability of energy or food sources near or on the artificial reef as the most important factor in the production of fish at artificial reefs.
Footage clearly illustrates 4 out of the 5 production events. The video shows herbivores grazing right on the platform, obligatory reef species feeding on plankton. Hundreds of algae eating fish can feed on the algae that grows on the platforms, while plankton eating species can feed on and off the platforms. The invertebrate communities living on the platforms are targeted by many species of schooling fish, which, in turn, are predated upon by many species of solitary predators which patrol the platforms and dine on the schoolers (1 & 2). The video demonstrates post-larval fish and juveniles of reef species utilizing the coral, sponge, and live rock for shelter from predation(3) (s The Texas-Louisiana continental shelf is characterized by a turbid bottom water layer and platforms extend hard substrate above this zone. The video displays diverse assemblage of tropical fish communities and these fish would not succeed (4) on the terrain dominated by an nephloid layer of clay and silt. Evidence for the 5th production condition involves the local natural reefs and most of the 4,000 oil and gas platforms in the Gulf of Mexico are placed in areas absent of natural reefs.
Clear Evidence for Production
Far more convincing evidence for production is the presence of shallow water Caribbean reef flora and fauna on hundreds of older platforms with a thick calcareous mat of live rock or coral. Fish residing at the platforms such as anglefish, brown chromus, spanish hogfish, blennies, and other obligatory reef fish are not readily available for attraction from natural sources yet they exist in remarkable populations. The video was shot on platforms in 100 120 m depths and 50-70 km from the nearest recruitment grounds in the flower gardens. The film illustrates the abundance of post-larval juvenile recruitment of coral reef species such as wrasses, damselfish, blennies, gobies, filefish, grouper, and many other reef fish. Planktonic fish can drift for weeks and even months, but, the numbers we are seeing are too great to be from one source so far away. You will notice on the video the large populations of Caribbean species such as, Creolefish, Bluetang, Brown Chromus, and Spanish Hogfish. The presence of large populations of shallow water, reef dependent juvenile and adult fish clearly indicates that the platforms are not attracting these organisms from natural reefs 70 km away but are producing these fish by supplying substrate essential to their success. Otherwise, if the platforms are removed, these populations of invertebrates will die immediately and the fish will be lost to the biota if they survive the process of mandatory removal.
Design of Platforms and Production
Japan has the most active and innovative sustainable fisheries program in the world, and they utilize offshore platforms and artificial reefs for the foundation of their most ambitious projects. Offshore platforms closely resemble their most sophisticated and expensive artificial reefs and they are 10 times stronger and 10 times bigger than the best Japanese designs. Offshore platforms span the entire water column and as they mature in the water, they become covered with a thick mat of coral and/or calcareous live rock. Platforms have an advantage over artificial reefs since they provide substrate up through the entire water column while regular artificial reefs are limited to relief on the ocean floor occupying only 10%-40% of the water column. The presence of substrate throughout the water column greatly increases species diversity and available sources of food.
Placement of Platforms and Production
Japanese researchers suggest that the availability of nutrient resources is a key variable in production of artificial reefs. Ideal conditions for artificial reefs exist along the Texas and Louisiana continental shelf where there are literally thousands of square miles of gently sloping, nutrient rich, ocean floor. The Mississippi River and other tributaries supply the region with nutrients and maintains the largest ground fish population in the lower Continental U.S.
The Attraction vs. Production Dilemma
To supply a universally accepted resolution, marine researchers must overcome the difficult and expensive task of quantifying the production of artificial reefs. The communities of the obligatory reef fishand the oil and gas platforms would not exist if the substrate was not present in the region. The larvae would have no place to settle, their food source would be eliminated, and they would loose their shelter on an barren continental shelf.
Essential Fish Habitat | Endangered Species Habitat | Federally Managed Species | Coral Habitat | Live Rock | Schooling Fish | Attraction vs. Production