Have you been diving around artificial coral reefs before? I personally love them a lot. Around such structures a lot of different marine life can be observed from the smallest critters, hiding away, to large fish assembling in schools around. And they often offer all that in areas where there wouldn’t be as much to see otherwise.
As scuba divers, when we hear “artificial coral reef” we tend to only think about those that were built for us, so we could have more fish, coral and other critters to see. Yet there are many other reasons to build these structures.
Reasons to build Artificial Coral Reefs
The first artificial reefs were built by the Persians to block passages for boats in ancient times (1).
Increasing Fish Yield
The next reason for artificial coral reefs was to increase the amount of fish in a specific area and with it the yield for fisheries (2). While this sounds like a great plan at first, it might also have negative effects. Read more about this below in the pros and cons section.
This is one of the main reasons to build artificial reefs today. Many reefs have been damaged by human (or natural) impact and researchers agree that this is a large threat to the oceans and also humankind. Coral reef restoration of any sort is an important tool to remedy these negative impacts.
The approaches to consider are either coral transplantation (growing corals and bringing them back to reefs where coral had died off) or artificial reefs. A common practice today is a combined approach of artificial reefs and coral transplantation to the structures (6).
Artificial reefs can help to prevent coastal erosion by either forcing waves to break further away from the beach or to hold sediment on the shallow areas (1).
Artificial reefs built to break the waves at a certain point allow more days when surfing is possible or create the perfect waves (1).
I don’t need to explain this one, right? We love to see a lot of life condensed in a small area which is typically seen around artificial reefs. So, of course, many scuba divers love to dive any type of artificial reef. Right, there are different types – but what are these?
Different types of artificial reefs
Every man-made underwater structure which allows coral to grow on it and a reef to form around it is an artificial reef. The structure provides a hard surface where algae and coral can become attached. Corals start to attach and with it small life will find its way to live between the structures. The small creatures will attract bigger fish and in the end the artificial coral reef will be teeming with life.
Ships, cars, trains, oil rigs, bicycles and other wrecks function as artificial reefs. Besides ships that sank in storms or wars in recent years, many were sunk on purpose to build artificial reefs and an attraction for divers. These wrecks are stripped from any harming structures on the inside and holes are created which allow easier entry for divers.
As well as wrecks, intact structures such as jetties often function as artificial reefs while they are still in use. These can be great for fish to hide and for scuba divers to take dramatic underwater photos.
Artificial Structures built using different Materials
These artificial coral reefs can be made out of different materials like concrete, rocks, wood, metal and similar. They are built in different ways depending on the purpose like increasing fish yield, breaking waves, protecting the shore, restoring reefs or entertaining scuba divers and snorklers.
Most structures that scuba divers encounter are built in a way that offers hiding places for marine life and simplify the attachment of coral. Sometimes even sculptures have been placed in certain areas to create underwater museums.
Studies are still ongoing to find the best material or combination of materials to build the perfect artificial reef.
Rocks are a natural ground to which coral can become attached and grow. Therefore this is an obvious choice providing it is the right type of stone (for example limestone). You can’t just throw any type of rock in the ocean and claim that you have built an artificial reef.
While wood does not last as long as other materials would, it is natural and in certain areas it already forms part of the underwater world.
Many modern artificial reefs are combinations of the above. I have just talked to a friend who explained that in their region in the US the tires have been removed and now more natural structures made out of rocks and wood have been used to replace them.
This is a special technique where an electrically conductive frame (for example wire mesh) is installed as an artificial reef and then a low voltage is applied on it. This causes a reaction that allows minerals naturally found in seawater to grow on the structure. The material is similar to coral reef and as long as the current is applied it will continue to grow. This causes the structure to become stronger and more rigid over time. The electrical fields and the protection offered by the structure attract a wide range of marine life. Coral attached to Biorock has been shown to withstand more dramatic conditions than coral in the natural reefs around them (3).
Rubble or Construction Debris
While some of these materials can offer a great basis for invertebrates to become attached, some can do more harm as the material may be toxic. 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.
Especially tires have been found to make fairly bad artificial reefs and in many places these reefs have had to be removed again. Read more about it in the pros and cons section.
Pros and Cons of Artificial Reefs
This all sounds amazing, doesn’t it? However there are possible negative effects of artificial reef structures too. The development of artificial reefs to provide additional habitat for marine life and restore lost coral reefs has been a trial and error process. Many projects failed and some even ended up in doing more harm than good.
Cons of Artificial Reefs
1. The material might become toxic
Many materials including rubber and metal will degrade or corrode releasing toxins into the water.
2. Tires didn’t make great artificial reefs
Huge amounts of old tires were sunk to the ocean floor in different countries. This was seen as a great way to get rid of the waste while building something great underwater. However, this did not work out as planned.
The tires don’t offer a good basis that invertebrates such as coral can become attached. Plus during storms or because the attachments to the ocean floor wear off the tires may get loose. They might then get washed up on natural coral reefs destroying the intact structures on their way towards shore. In many areas the tires have now been removed again (4).
3. Overfishing instead of increasing biomass
Another concern with artificial reefs is that they don’t actually increase the amount of fish, but concentrate them around a specific area. The higher fish concentration makes it easier for fishers to catch them. This might even increase the overfishing problem instead of helping the marine life (4).
To avoid this artificial reefs, maybe all reefs, should be protected and fishing only allowed at a certain distance from the structure.
4. The artificial reefs might be different to natural ones
Researchers compared the marine life around two shipwrecks (one five and the other 105 years old) with natural reefs in the same area. They found that the “artificial and natural reefs strongly differ in their trophic structure, both in their multivariate composition and in biomass of most guilds”.
In other words the type of marine life as well as the amount differs between the two. This means that ship wrecks might not be suitable as a replacement for lost natural reefs and the ecosystem around it is different than on the natural reefs. This might be true for other artificial reefs as well (5).
There are also concerns that certain artificial coral reef structures might actually attract fish away from natural coral reefs creating an imbalance in the natural habitat.
Pros of Artificial Reefs
Ok wow, so many cons! I actually had no idea until recently. When I posted the video of friends creating an artificial reef using tires I got a comment that this might not be the best idea. I didn’t know and therefore started to do some research. That was when the idea for this article arose.
While there is a lot of research ongoing as to how to build the right artificial reefs to improve the state of the oceans, there are no studies that can prove an actual positive impact on larger regions. Yet it is one of our best approaches to help the oceans recover from reef loss and the subsequent decrease in biomass.
I am sure that locally artificial reefs can have a positive impact and we all agree that they make great dive site.
1. Coral Reef Restoration
Artificial reefs play a central role in the restoration of coral reefs that have been destroyed by human impact or natural disasters like storms or El Niño.
Using the right material for the structures which is similar to a natural basis for coral growth and transplanting coral to it allows restoration of lost reefs hopefully faster than they would regrow naturally.
2. Strong against erosion
While shallow areas consisting of sand and gravel might be washed off in strong currents and big waves the artificial reefs can be built to withstand such impacts. Therefore such structures can make shores more stable against erosion.
3. They attract tourists
From surfers to snorkelers to scuba divers – the artificial reef help attract more tourists to a destination. The economic value will increase the interest in protecting the ocean even more.
So even considering all the cons artificial reefs are a good way of trying to improve the underwater ecosystem and a lot more research is necessary to find the best way to do so. While we are in the process of finding good options of restoring habitats for marine life, artificial reefs are a good start as long as they are not toxic and are properly attached to the ocean floor.
I might not need to mention here that we would be better to take measures before restoration becomes necessary, but it seems we have already passed this point.
How to build an artificial reef
I was lucky enough to watch two different groups of divers putting down artificial reefs in Bali. The area of the artificial reefs here is black sand with some rocks. The trickiest part is to then get coral to grow on the formation.
The area also suffered from warm waters during El Niño in 2016 causing many of the hard corals to bleach and eventually die off. Also some of the coral planted to artificial reef structures. However, even without coral, fish will most probably hang around as they can find shelter there.
See the video below on how the divers have to work hard in order to put the structures in place in Tulamben, Bali.
To see the artificial reefs around Tulamben follow this link.
1 Artificial Reefs (2016) in Wikipedia. Retrieved January 21, 2017 from https://en.wikipedia.org/wiki/Artificial_reef
2 Artificial Reefs (2011) in National Geographic. Retrieved January 21, 2017 from http://ngm.nationalgeographic.com/2011/02/artificial-reefs/harrigan-text
3 Biorock (2016) in Wikipedia. Retrieved January 21, 2017 from https://en.wikipedia.org/wiki/Biorock
4 Florida Raises Ill-Fated Artificial Reefs (2007) in Environmental News Network. Retrieved January 20, 2017 from http://www.enn.com/top_stories/article/6895
5 Simon, T., Joyeux, J., Pinheiro, H. (2013). “Fish assemblages on shipwrecks and natural rocky reefs strongly differ in tophic structure” In Marine Environmental Research. 90:55-65
6 Avigdor Abelson (2006). “Artificial reefs vs coral transplantation as restoration tools for mitigating coral reef deterioration: Benefits, concerns, and proposed guidelines” in Bulletin of Marine Science. 78(1):151-159