A full 25 percent of all the marine life on the planet calls coral reefs home. But around the world, these natural habitats are in trouble. According to World Wildlife Fund, about one-quarter of coral reefs are considered damaged beyond repair, with another two-thirds under serious threat. Climate change, with its attendant rising sea temperatures; overfishing; pollution; careless tourism; and destructive fishing practices, such as blast or dynamite fishing, cyanide fishing, bottom trawling and muro-ami (pounding and crushing corals to scare fish, driving them toward nets) are all speeding coral deaths.
Almost a billion people live near corals, relying on them for food, protection from storm surges and the income that tourism brings. And we’ve only just begun to understand how reefs might contribute to medicines, such as those to treat cancer and HIV.
With natural reefs diminishing, artificial reefs are now increasingly gaining favor. These structures usually take the form of sunken ships, decrepit oil platforms or other human trash. But while building artificial reefs sounds like a good remedy for alleviating the loss of natural ones, will the practice be healthy for the environment and us in the long term?
Turning trash into treasure
Coral reefs are a big part of the ocean food chain. Occupying less than a quarter of 1 percent of the entire marine environment, they can yield an average of 15 tons of fish and other seafood per 0.38 square miles each year.
While a coral may look like a single entity, it’s actually a partnership between two microscopic organisms: a polyp, which is a tiny assemblage of mouths and tentacles; and a single-celled organism, usually an alga or dinoflagellate, which lives within that assemblage. The polyp builds a tiny calcium-carbonate structure that shelters the alga; and through photosynthesis, the alga provides food to the polyp. Millions of these little partnerships accumulate to form enormous, iconic coral reefs.
But warming waters due to climate change can cause corals to expel their algal partners. The corals then turn bone white and die—a phenomenon called “bleaching.”
According to the National Environmental Education Foundation, over the last century, global sea surface temperatures have risen by about 1.5 degrees Fahrenheit. And during the past three decades, sea surface temperatures have exceeded the last century’s average every year. To put that in perspective, from 1876 to 1979 only three coral bleaching events were recorded. From 1980 to 1993, there were 60.
This decline of coral reefs has had huge ecological and economic consequences. An estimated one billion people have some dependence on coral reefs for food and income from fishing. If the reefs vanished, hunger, poverty and political instability could ensue. Commonly consumed species of fish, such as grouper and snapper, could disappear altogether, while oysters, clams and other creatures—vital to many people’s diets—would also suffer. Commercial fisheries would not be able to meet the demand for seafood.
In Florida, for example, more than 500 species of fish live and depend on coral reefs. In a state that is no stranger to storms, healthy reefs buffer up to 90 percent of the force of incoming waves, thus preventing coastal erosion. Just in the Florida Keys alone, more than 33,000 jobs are dependent on ocean recreation and tourism, which accounts for 58 percent of the local economy and an average of $2.3 billion a year.
That’s why Florida has deployed derelict autos and old refrigerators in the Gulf of Mexico. Hard surfaces—whether natural coral or man-made—appeal to tiny creatures. Steel structures, especially, are soon covered by calcareous algae that provide an adequate surface on which coral larvae can grow quickly. Once corals colonize their surfaces, the reefs attract even more marine life—crustaceans, fish, mollusks and sea urchins—seeking food and shelter. In the waters off South Carolina, retired army tanks, barges, bridge debris, tugboats and other concrete structures now make up more than 45 man-made reefs. The state of New York has sunk retired subway cars in the Atlantic in hopes of creating artificial reefs, and researchers in the Red Sea have found that several shipwrecks have become thriving coral communities.
These artificial reefs then attract diving tourists, easing human pressure on natural reefs. Artificial reefs can even enhance the development of rare coral species that are not often found on natural reefs.
Creating an underwater junkyard
Disposing of our trash in the world’s waters, however, isn’t without risk. There is a possibility that the metal structures can contribute to toxins in the ocean, which can affect and accumulate in any of the species that colonize the reefs. Anglers may be catching and consuming fish that have absorbed contaminants, such as carcinogenic polychlorinated biphenyls (PCBs), as well as asbestos, oil and other pollutants leaching from sunken vessels.
Too, dropping large objects into the sea to serve as artificial reefs can damage preexisting habitats or displace wildlife from their homes. According to The Guardian, an artificial reef composed of disused tires ended up coming apart, distributing one to two million tires throughout the sea and causing damage to natural reefs, boats and the shore. If not anchored to the bottom sufficiently, an artificial reef could be moved by strong storms and currents, perhaps causing harm to natural reefs. And since the deployments of some of these artificial reefs are not indicated on any maps, boat collisions are a possibility. The safety of diving on decommissioned vehicles and vessels is often questionable.
Another concern with artificial reefs is that they don’t actually increase the amount of fish, but that they instead concentrate them around a specific area. This higher density of fish not only aids in the spread of fish diseases but makes it easier to catch them, adding to the overfishing problem. And, certain artificial reef structures might actually attract fish away from natural coral reefs, creating an imbalance in the natural habitat.
In an article published in ScienceDirect in 2013, researchers comparing the marine life around two shipwrecks (one five years old and the other 105) with natural reefs in the same area found that “fish assemblages on artificial and natural reefs differ in trophic structure.” The type of marine life as well as the amount differed between the two. Artificial reefs may cause nonindigenous species to proliferate, depleting the organisms that these species feed on. Other research observations indicate that many artificial structures, such as the sides of docks, harbors, and oil and gas platforms, are quickly becoming habitats and possibly spawning grounds for invasive species, such as the orange cup coral.
Once dropped in the water, artificial reefs require monitoring to track their impact on the environment and maintenance needs. Who will provide these costly services? There is also a risk that debris would just be dumped in the ocean as an easy way to get rid of it without actually providing much benefit.
As it usually is with nature, conserving what we have is often the smarter course of action compared with trying to recreate what we have lost.
Here’s to finding your true places and natural habitats,
Coral reef did benefit our life, no matter in marine life diversification, daily food source or job offering. Personally, I don’t like artificial reef. Because it originally was a kind of trash make by human misbehavior in the ocean. It will never function like a real coral reef. This year, the Great Barrier Reef faces unprecedented wide range of bleaching caused by climate change. Hopefully, it is still able to recover. It is a good article, thanks for sharing.
More long term research will probably answer this. Preserving and making coral reefs back as they once were is an urgent conservation matter.
This article highlights to me some very real concerns and the need for longer term ecological monitoring of marine impact mitigation measures.
It will be a great challenge to the scientists really.
It is a well-rounded article. I can say as both a Florida resident and marine biologist, that the success of the artificial reef projects I have enjoyed here have yielded amazing results in a very short period of time. The research I have done specifically into old ships that are intentionally scuttled did explain that those ships are carefully prepared (i.e. removal of oil and other leeching substances) before sinking but long term research is the true test. Thank you for sharing!
While reading this article, I went back and forth a few times on what I thought about artificial hard surfaces underwater. Wound up in consensus with your opinion at the end. It sounds kind of like having a lot of folk art in your lawn. Maybe the charm wears off quicker than you’d think. Risks and maintenance seemed to outweigh the long term costs. It’s an interesting stop gap measure to be sure… maybe in 100 years’ time we’ll find a better solution, even with a warmer ocean.