Fish Production of Artificial Reef to be Studied
March 5, 2004 - Updated February 2, 2005
Contact: Christina S. Johnson, csjohnson@ucsd.edu, 858-822-5334
(This Story first appeared in the Coastal Conservancy's magazine, Coast & Ocean.)
Kelp bass (Paralabrax clathratus) swimming in the canopy of giant kelp (Macrocystis pyrifera).
Since 1958, the Department of Fish & Game has participated in the construction of more than 100 reefs at 33 sites in Southern California.
Constructed by sinking old wooden streetcars, automobiles, tires, barges, cement pipes, cement boxes, concrete rubble and quarry stones, these early reefs were meant to provide an underwater landscape that would attract fish by giving them intriguing nooks and crannies for hiding and foraging.
The reefs, in theory, had two potential benefits: they enhanced sport fishing and offset pressures on fish stocks by providing fish with added habitat. But, although the Department of Fish & Game reports that the state's artificial reefs have been highly successful at enhancing sportfishing by congregating fish, there are still questions about whether these reefs actually benefit the marine ecosystem by increasing fish populations.
This summer, two studies will attempt to quantify fish production – the number of fish born and raised on a reef – at what will become the state's largest artificial reef, located near the San Onofre nuclear power plant in southern Orange County. The studies are being funded by the National Oceanic and Atmospheric Administration's California Sea Grant, the Department of Fish & Game, and Southern California Edison.
Sheephead (Semicossyphus pulcher) and a school of blacksmith (Chromis punctipinnis) foraging near the bottom on the San Clemente Artificial Reef.
(Photos on the San Clemente Reef by Richard Herman)
The findings, besides answering detailed scientific questions, will help evaluate whether artificial reefs benefit nearshore reef-dwelling animals and plants enough to warrant their use as mitigation tools in Southern California. If artificial reefs do not, as currently designed, boost fish production, they may be contributing to declining fish stocks by aggregating them for fishers.
The history of artificial reefs in California began in 1958, with the construction of Paradise Cove Reef in Santa Monica Bay, the state's first artificial reef designed specifically for sportfishing. The reef was made by submerging 20 discarded automobile bodies. It appeared to work: Within hours of the reef's completion, marine biologists reported seeing surfperches, sargos and small California halibut.
Later, according to the Department of Fish & Game, fish that had not been seen in the area, such as opaleye and sheephead, were observed over the cars. Because so many fish were observed around the reef, a set of experimental reefs, made of wooden street cars, more car bodies, heaps of quarry stone and cement boxes were later built at Redondo Beach, Malibu, Santa Monica and Hermosa Beach.
The company is building the state's largest artificial kelp bed, in shallow waters near the nuclear power plant. California Sea Grant is funding research to evaluate whether artificial reefs can be built to increase fish production. Photo Credit: Southern California Edison
Quarry stone was demonstrated to be the best material for reef design since it does not corrode in salt water and provides excellent substrate for plant and animal life. Subsequently, the Department of Fish & Game built a series of quarry stone reefs in several locations off Ventura, Santa Monica Bay and Orange County. Quarry rock was also placed at the outer perimeter of seven Southern California fishing piers. Almost all the quarry stone used for the reefs is mined from Catalina Island.
A second wave of reef construction occurred in the 1980s. Reefs built during this time were designed to examine how the placement of reefs – their spatial arrangements, heights and depth below the sea surface – influenced plant and animal life.
Among many things, biologists found that flatter, lower relief reefs facilitate giant kelp forest growth, while taller reefs attract more fish. Modern reefs are usually made of concrete and quarry stone and are typically between two feet and 10 feet high.
Many of the old, original reefs built with steel or wood materials have rusted and rotted away over time.
Photos provided by Richard Herrmann, a San Diego resident and internationally noted nature photographer whose work appears in many major wildlife and nature publications. The photos in this column were taken on the San Clemente Reef
And, in recent years, only a few new reefs have been built, although many reefs have been expanded by adding concrete rubble, often from demolition projects near harbors.
Despite all the reef studies over the last four decades, nobody has been able to answer the age-old question: Do the reefs actually increase fish populations or merely congregate fish? As environmental groups have asked: Is California cluttering its shallow waters with debris, or enriching the marine ecosystem?
"There is a whole debate on production versus attraction," said Steve Schroeter, a biologist at University of California, Santa Barbara, who specializes in artificial reef dynamics. "Are you simply attracting things or actually increasing overall populations? It is a really hard question to get at and a complicated problem."
The general idea behind reef construction is to mimic the benefits of rocky habitat – to provide hard substrate for fish recruitment, algae growth and invertebrate colonization.
In California, rocky habitat is considered the backbone of the most biologically diverse marine habitat – the giant kelp forest, which except for the Santa Barbara area, is associated exclusively with rocky reefs. Many of the most commercially valuable marine products – lobster, abalone, and urchins for instance – are also associated with kelp forests.
In Northern California, where the nearshore ocean floor is narrower, slathered with rock shelves and boulders are more abundant, there is no reason to build artificial reefs.
For this reason, nearly all the reefs ever built in the state are located in Southern California in San Diego, Orange, Los Angeles and Ventura counties in areas where the ocean bottom is sandy and the continental margin is wide, and where sun-drenched weather is ideal for boating almost all year round.
To help determine whether artificial reefs do increase fish production, biologists at San Diego State University, the University of California, Santa Barbara, and the Department of Fish & Game are conducting fish surveys at what will become the state's largest artificial reef.
The reef is being built in southern Orange County by Southern California Edison as mitigation for damaging kelp beds near its nuclear power plant in San Onofre.
Mitigation refers to a regulatory process in which builders are forced to compensate for ecological damages caused by their projects by restoring similar habitat elsewhere.
At present, the reef being built near San Onofre consists of a grid of low-relief stone and concrete piles, consisting of seven 3.2-acre clusters. Within each cluster, there are eight different reef designs, represented by varying the relative proportions of quarry stone and concrete.
Eventually, the areas between the seven clusters will be filled in with hard material to provide substrate for a 150-acre giant kelp forest, which it is hoped will teem with bass, lobster, rockfish, sheephead, crab, urchin, and maybe one day, abalone.
In the meantime, the rocky islands are providing a rare opportunity to examine how fish production varies with reef design and between man-made and natural reefs.
Beginning this summer, Assistant Professor Todd Anderson at San Diego State University and his graduate students will begin conducting diving surveys to track populations of very young fish.
Unlike large, freely swimming fish, young fish are unable to migrate between the rock islands. Their abundance thus represents a better estimate of fish production than populations of adult, highly mobile species.
"If the artificial reefs are truly increasing fish production in the area, fish production should be greater on the artificial reefs than on the natural reefs," Anderson said. If fish production – measured by looking at a combination of recruitment, growth, fecundity and survival rates – is lower on the artificial reefs, then one could argue that the fish would have been better off settling over one of the natural reefs nearby.
If, on the other hand, fish numbers are limited by a lack of rocky habitat, as may be the case in the sandy-bottomed waters of Southern California, artificial reefs may enhance fish abundance even though fish production is lower on the artificial reefs than on the natural reefs, he said. There is really no way to tell if rock habitat is a limiting factor in fish abundance.
Fish abundance, however, is not the only concern. Another is whether artificial reefs will support the same assemblages of plant and animal life as natural reefs. Preliminary diving surveys, conducted by Schroeter and colleagues, have shown that bottom fish are more abundant on artificial reefs than on natural reefs, while kelp canopy fish are relatively less abundant.
Schroeter attributed these differences to the fact that the artificial reefs have fewer large, adult kelp plants on them. He said that this difference may become less noticeable in time as kelp spores continue to colonize the artificial reefs and existing plants grow. The reef was built recently, in the fall of 1999.
This summer, Dennis Bedford with the Department of Fish & Game will begin tagging California sheephead, a fish under pressure by the live, finfish fishery. He will tag fish with sonic implants and with traditional bands. His project is an extension of work he conducted at an artificial reef near the Camp Pendleton Marine base in northern San Diego County. His goal is to be able to track the sheepheads‚ ranges, their survival rates and from this to estimate their abundance per unit area on the reefs.
Bedford said, "We want a number that tells us how many pounds of fish are produced at the reef per unit acre. This is the quantitative number that everyone is looking for. We want to be able to tell managers how many fish they will have if they build some quantity of reef."
Dave Parker is a senior biologist with the California Department and Fish & Game who supervises the agency's artificial reef program. He said that Los Angeles and Long Beach port authorities have both shown interest in mitigating for future port maintenance projects by building artificial reefs.
"Up 'til now, the thinking has been to restore or buy wetlands in places such as Bolsa Chica in Huntington Beach," he said. But the supply of these wetlands is limited. More than 90 percent of the state's wetlands have been paved or filled.
As a mitigation tool for port projects, artificial reefs are controversial since the reefs are meant to enhance nearshore, rocky habitat while most port projects impact wetlands and lagoons, totally different ecosystems.
Leslie Ewing, a senior coastal engineer with the California Coastal Commission, which oversees mitigation projects along the coast, said that artificial reefs will need to be evaluated more closely before they can be considered for "out of kind mitigation."
Parker said, "If the Edison reef shows that it has been successful, more people will look at reefs as ways to mitigate. But that is a ways off, I think."
.gif){kind=logo}
