Coral reefs are home to 25 percent of ocean biodiversity and, at the same time, make up less than 0.2% of the seabed surface. Unfortunately, it is not news anymore that coral reefs are in trouble.
For decades, we have witnessed a sharp increase in coral bleaching events and various other means of reef devastation.
Although there is a chance for a bleached reef to recover, once the living coral is weakened or completely gone, sea storms and the changing water chemistry have no trouble eroding the magnificent calcium-carbonate skeletons, which are a foundation to which the reef life attaches itself.
Once these structures disintegrate, the hope for reef revival is also gone.
Why artificial coral reefs are vital
Although the ocean is vast, the surfaces the corals can attach to and start reefs are scarce. That is why people interested in reef conservation have begun experimenting with creating (or simply sinking) artificial coral-friendly structures to give corals and other creatures a potential habitat for reef building.
In time, a thriving artificial reef will be teeming with life, plus provide an interesting diving point.
After decades of trial and error (and quite a lot of it), it is safe to say that we now know what manufactured structures really work for creating artificial coral reefs and what does more harm than good.
Studies show that an artificial reef can create a community that mimics the neighboring natural reef when built and positioned right, provided that the two have similar structural features.
Some newer, custom-designed reef structures have been shown to harbor twice as many fish species as natural reefs or older artificial designs – although the artificial ones are still inferior in terms of fish population density.
Here’s a short overview of artificial coral reef origins and a glimpse into a rich history of failures and successes.
The history of artificial coral reefs
The logic behind artificial reefs has been around for thousands of years, although the purpose of the first reef-simulating constructions wasn’t to increase biodiversity. Living off the sea, people of the Indo-Pacific islands noticed that putting simple bamboo and palm leaf structures into the water attracts fish.
That is just one of the first examples of fish attraction devices or FADs. All primitive FADs used similar materials and techniques.
However, FADs were miniature artificial habitats and not large-scale structures that can host a community. The first known intentional artificial reef creation occurred in 18th century Japan, where multiple “reefs” from bamboo and leaves were sunk. A century later, the idea was further developed in the West, in tune with the science of the time.
Charles Darwin: an early coral reef theorist
Charles Darwin was among the first coral reef theorists who provided great input on the reefs’ origins and functioning. For example, he described the mechanism of reef structure creation, especially of coral atolls, dismantling the idea at the time that the circular structures had something to do with volcanic activity.
“In time the central land would sink beneath the level of the sea & disappear, but the coral would have completed its circular wall. Should we not then have a Lagoon Island?– Under this view, we must look at a Lagoon Isd as a monument raised by myriads of tiny architects to mark the spot where a former land lies buried in the depths of the ocean. “ (Charles Darwin, 12th. April 1836, Beagle diary, pp. 399-400).
Besides taking notes, Darwin also actively experimented with the “myriads of tiny architects” and was probably the first to observe FAD-like structures through a lens of coral reef building.
In an experiment, he attached dislodged corals to bamboo stakes. He then noted that the attached corals survived, unlike the ones left to roll on the seafloor freely.
Even though bamboo would be a very short-lasting base for corals, Darwin was the first to propose and prove that artificial structures can indeed provide a stable environment for coral survival. That is why he is sometimes credited with being the first coral reef conservationist and restorationist.
First publication on how to design artificial reefs
At about the same time in the 1830s, the idea of artificial reefs took off in the United States, first in the context of FADs.
The 1855 “Ichthyology of South Carolina” by American naturalist John Edward Holbrook was the first publication to describe designing artificial reefs – in a South Carolina site damaged by on-land development. The reef was created from locally-sourced natural materials – mostly large tree branches and leave – to re-attract the fish community.
However, in the 20th century, the first real cue for creating artificial reefs from man-made materials came from divers exploring the old sunken vessels that were exceptionally rich with sea life and very reef-like.
As the awareness of the sea biodiversity grew, the notion of artificial reefs became very popular, especially in the US, Southeast Asia, and Australia. However, it was a bumpy ride to get to the genuinely beneficial artificial reef designs and repurposing projects.
As the industry and mass production developed, companies and engineers came to the idea of repurposing solid objects or byproducts as a fundament for building reefs. That will prove itself to be a bad idea – or even catastrophic in some instances – for several reasons.
First, many companies saw and seized artificial reef creation as an opportunity to dispose of their waste and/or gain positive publicity. Secondly, it was largely unknown if the chosen materials would be able to serve the purpose or if they would pollute the waters.
Of course, it turned out that dumping a bunch of solid objects into the sea would not magically create a new reef. Quite the opposite – some of these actions severely damaged the local marine environment.
One of the most infamous examples is Florida’s Osborn Reef. Initially, the basis for the reef was constructed in the early 1970s using 50-foot diameter concrete jacks. However, shortly after, Broward Artificial Reef Inc. proposed that the construction should be expanded by using old automobile tires in an effort to “recycle them” and double or triple the surface for marine life.
The idea was embraced by the Broward County government, the US Army Corps of Engineers, and tire producers and approved in 1974. Consequently, over two million tires attached with only steel clips were dumped into the sea about 7,000 feet (2,100 m) offshore, covering 36 acres (15 ha) of the ocean floor.
However, the steel clips corroded relatively quickly, leaving the tire structure to be dismantled by ocean currents and storms. Rubber was an unsuitable surface for coral attachment from the beginning, but the structure destruction led to the demise of any creatures that did manage to attach themselves. The loose tires had spread across the ocean floor and begun washing ashore, even reaching far away beaches like those in North Carolina.
The studies done decades later showed that nearly no fish were living in the Osborn Reef area, that the tires were moving around all the time, and that they were leaching toxic chemicals.
Unfortunately, the results weren’t noticeable quick enough, so many similar projects were carried out in Southeast Asia, Australia, and the US in the 1970s and 1980s, with similar epilogues.
Since 2001, the Osborn reef has been subjected to an extensive, expensive, and ongoing cleanup. About a third of the tires have been removed up to this date.
Similarly flawed are the plastic pipe reef projects of Southeast Asia, often sponsored by PVC pipe producers. These structures are often broken or overturned even by average storms, are not suitable for the attachment of corals, start to release toxic compounds over time, and lack any ecological or aesthetic value.
Besides inappropriate materials such as tire rubber or PVC, the issue with these structures is that they are created from many smaller pieces, making them easy “prey” for sea storms. For example, all projects that utilized small, scrap concrete blocks ultimately failed, despite using a suitable artificial reef material, in theory. The notion of “one man’s trash, another man’s treasure” doesn’t hold for coral reefs.
However, some efforts did prove surprisingly successful, despite looking equally reckless on the outside.
Old heavy steel vehicles and vessels – ships, subway cars, or even tanks – have proven to be a good foundation for reef creatures.
Nearly every child’s sea-themed illustration or storybook features a picture of a sunken ship, usually inhabited by sea creatures. That sunken ship is actually a legitimate artificial reef, even though it didn’t end up at the sea floor with that particular intention.
Many steel warships and blockships that were sunken in the First and Second World Wars are now teeming with sea life, and the divers noted that. But divers couldn’t spot them all – some ships were so covered with coral and other sea life that it wasn’t until the LIDAR technology came into the scene that their true origin was discovered.
The trick with thick, heavy gauge steel is that it is corroded by seawater sufficiently so that it gains a texture suitable for coral attachment, but still, it doesn’t degrade too fast – the steel base can persist for at least a century. On the other hand, vehicles and aircraft made from metal alloys are not as nearly successful since seawater chemistry causes alloy bonds to disintegrate, leading to preterm vehicle decomposition.
Since the mid-20th century, many old vessels – especially military – were purposefully sunk with the intent of creating living coral reefs.
Florida has one of the most active artificial reef programs – staggering 3,800+ public artificial reefs have been placed in state and federal waters. Florida’s artificial reef projects are largely supported by Florida Fish and Wildlife Conservation Commission’s Artificial Reef Program.
The Osborn Reef catastrophe indeed happened off the coast of Florida, but the Sunshine State has plenty of shining success reef stories as well.
Thunderbolt artificial reef
The Thunderbolt was a US-built World War II defense ship. In 1986, it was deliberately sunk four miles south of Marathon and Key Colony Beach in Florida at a depth of 120 feet (36.6 meters).
Nearly 40 years later, it hosts many trademark coral reef organisms – corals, other hydroids, and sponges. These provide food and habitat for a variety of other sea creatures.
Great Carrier Reef
Another retired warship, USS Spiegel Grove, was sunk in 2002 in the waters off of Key Largo. Measuring 510 feet (155.45 meters) in length, USS Spiegel Grove was the largest ship to be sunk for artificial reef creation at the time. This year, the 20th anniversary of the descent and reef creation were appropriately commemorated.
In 2006, the record-holding USS Spiegel Grove was surpassed by the USS Oriskany, a retired aircraft carrier that measured 888 feet in length and 30,800 tons in weight. Today, it still holds the title of the largest vessel sunk to create an artificial reef.
The artificial reef is located in the Gulf of Mexico, 24 miles off the coast of Pensacola (you’ve guessed it), Florida, and the colonization by organisms such as coral, algae, and mussels has for now been successful.
Another fun fact is that it has been nicknamed the “Great Carrier Reef” as a reference to its origin and an analogy to the largest coral reef in the world – the Great Barrier Reef of Australia.
St Pete (or St Petersburg) Beach Reef
But Florida’s coasts hide more than ships. In 1995, in an action that looked more like an old Top Gear stunt than a marine engineering project, ten US Army tanks were driven into the sea off St Petersburg, FL coast.
Today, they are a part of the site known as St Pete (or St Petersburg) Beach Reef. The central part of this reef was created using concrete blocks from Skyway Bridge and Old Corey Causeway in 1976.
Later, additional reef foundations were installed. Besides the tanks, a decade earlier, a 200-feet long steel barge was sunk with the same intention. Today, the site seems to be thriving.
Here is one of the St Pete Beach Reef tanks in 2017:
It should be pointed out that the modern practice obliges that all the ships and vehicles to be sunk are inspected by the responsible agencies (usually the EPA) and cleansed of any potentially polluting or otherwise unsuitable materials and substances before sinking.
Although the practice hasn’t been abandoned, the idea of artificial reef design has now evolved beyond sinking obsolete ships and other structures.
In recent years, many companies, startups, and initiatives have created elaborate structures from provenly successful reef-building materials, and marine scientists have kept researching to help determine how successful these are in preserving the coral reef biodiversity.
The truth is that modern artificial reef designs have become so elaborate that they deserve an article of their own.
A school of thought says that building artificial reefs is trying to fight the symptom and not the “disease” – the rampant climate change, marine pollution, and all the other human activities that catalyze the demise of irreplaceable natural coral reefs.
However, reports and scientific studies are increasingly showing that artificial reefs can, in fact, be a sanctuary or a boost for local marine biodiversity. But only up to a point – if the trends continue, no amount of sunken barges, tanks, and state-of-art custom-made reef structures will be able to preserve the richness of coral reefs for future generations.
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