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Artificial Reefs, Real Diversity

by Liz Clift

I was in middle school when Titanic hit movie theaters. The RMS Titanic, which sank in April 1912, rests more than two miles below the surface of the water, off the coast of Newfoundland. And while the footage in the early scenes of the movie showing a submerged ship turned artificial reef are largely recreated, it provides a general idea of what the shipwreck reef actually looks like (note, the linked video is also clearly manipulated with ghostly figures to tug those heartstrings).

Bow of Titanic, NOAA 2004

But as an aspiring marine biologist getting my feet wet (very literally) with freshwater ecology, I loved the idea of other animals reclaiming our wreckage—an idea which was gaining traction in restoration projects.

In the pond near my parents’ house, a dumped Christmas tree was an ideal spot to catch minnows (or sometimes young bluegill) and baby turtles. Although the Christmas tree in that pond was simply dumped—probably because a neighbor missed the cutoff for the city collecting Christmas trees—using people’s Christmas trees to create artificial reefs is something that fisheries program managers actually do. Beginning in 1992, at Lake Havasu in Western Arizona, a large habitat recovery program began to use discarded Christmas trees to create habitat* for young fish. Over the course of a decade, 875 acres of artificial reefs were created from cinderblocks, PVC pipe, concrete sewer pipe, and Christmas trees.

And the results were astounding. When the project started, divers monitoring these artificial reefs could “count all the fish at any spot on their fingers.” But, as time passed, these artificial reefs developed into sustaining habitat, a place for fish to spawn, breed, and grow to maturity. And sure enough, as the fish populations grew, so did the artificial reefs popularity as a local fishing destination.

Since Christmas trees take five or six years to decompose under water, the project is replenished with approximately 500  new trees every year—and more places are picking up the program. These Christmas tree reefs create fish nurseries, which are places for young fish to hide from larger fish and other predators. The algae, which grows on the decomposing trees, helps feed aquatic insects which feed a variety of fish and other aquatic animals, and can help oxygenate the water. (Too much algae can result in eutrophication, but that’s another blog post.)

Of course, Christmas trees are far from the only way to create freshwater reefs.

In Lake Michigan, there have been efforts to displace invasive species like alewives, round gobies, and the rusty crayfish through the creation of artificial reefs filled with cobble. This cobble is the appropriate size for native fishes, such as lake herring and lake trout (which have both maintained remnant populations for more than half a century). The folks leading this effort hope that by displacing the invasive populations of alewives (whose bodies contain an enzyme that makes their predators unable to reproduce) and developing a better understanding of how round goby and rusty crayfish interact with the reef through additional study, native fish populations will be able to rebound.

This, in itself, is an argument for making sure that restoration and conservation projects always include ecologists and biologists.

Similar projects are underway in other parts of the Great Lakes. And, those of us in the field of ecological restoration should take note. My guess is that if you’ve never lived in the Midwest, you probably don’t think about the Great Lakes all that often—but if you’re interested in artificial reefs, perhaps you should. Not only are these projects scaling up, they’re also providing plenty of research about what works and what doesn’t in these particular freshwater environments.

The Great Lakes offer a huge study area. Collectively, they have more than 95,000 square miles of surface water, enclosed in almost 8,000 miles of shoreline. And, they house an estimated 5,000 shipwrecks (which, we know in marine environments, can be the basis for impressive artificial reefs).

Many of the Great Lakes shipwrecks are accessible to Open Water-certified recreational divers and snorkelers (and even, in some cases, swimmers). The filtering capacities of invasive mollusks, like the zebra mussel and quagga have improved underwater visibility—which means that these wrecks are easier to see and photograph. Several just off the coast of Chicago, like the 200-foot long ferry, Straits of Mackinac and the shipwrecks near the Morgan Shoal, are being colonized by underwater life.

Although in the Great Lakes you’re not going to find the bright colors (or warm waters!) that would characterize a Caribbean shipwreck or decommissioned, near-shore oil platform in warm waters, that doesn’t mean these and other artificial reefs aren’t dive-worthy or of ecological and economic importance.

Regardless of whether an artificial reef occurs in a freshwater or marine environment, they add definition to the environment—textures, patterns, crevices, footholds, where before there was little or none. Life takes hold on these structures (often quite literally in the case of mollusks and some cnidarians), and life begets more life.

Providing more consideration to the potential benefits of artificial reefs is becoming increasingly important as incidents of coral bleaching, dredging, coastal run-off and proliferation of invasive species continues to occur.

At Great Ecology, we help design freshwater systems that encourage increased biodiversity and structural diversity, and have worked to improve the ecological function of a variety of freshwater ecosystems ranging from mountains streams, to lakes, to the mouths of rivers.

Through our partnership with Blue Latitudes, we also specialize in helping clients plan for end-of-life for marine structures, including oil and gas platforms. Check out our Platform Decommissioning services page to learn more about this work.





*Christmas trees have also been used to help create dunes—and while I like the story of Lake Havasu, the largest freshwater habitat recovery program of its time, similar programs were also starting up elsewhere.



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