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Artificial Reefs

NOAA Ocean Podcast: Episode 75

Not all reefs in the ocean are naturally occurring. Artificial reefs are human-made structures that come in a variety of shapes and sizes. In this episode, we learn about what they are, the benefits they provide, and how the first study was conducted to calculate how much of the seafloor is covered by these reefs. Our featured experts are Avery Paxton, research marine biologist with NOAA’s National Centers for Coastal Ocean Science (NCCOS), D’amy Steward, NOAA Sea Grant Knauss Fellow, and Chris Taylor, research ecologist with NCCOS.

In 1986, the Thunderbolt was intentionally sunk in 36.6 meters (120 feet) of water four miles south of Marathon and Key Colony Beach in Florida. The ship’s superstructure is now home to colorful sponges, corals, and hydroids, providing food and habitat for a variety of sea creatures.

In 1986, the Thunderbolt was intentionally sunk in 36.6 meters (120 feet) of water four miles south of Marathon and Key Colony Beach in Florida. The ship’s superstructure is now home to colorful sponges, corals, and hydroids, providing food and habitat for a variety of sea creatures.

Avery Paxton

Avery Paxton

Research Marine Biologist, Marine Spatial Ecology Division, NCCOS
D'amy Steward

D’amy Steward

Sea Grant Knauss Fellow, Congressional Affairs Fellow, Office of Legislative and Intergovernmental Affairs
Chris Taylor

Chris Taylor

Research Ecologist, Marine Spatial Ecology Division, NCCOS


HOST: This is the NOAA Ocean Podcast. I’m Marissa Anderson. You may be surprised to learn that not all reefs in the ocean are naturally made. Artificial reefs are human-made structures that can come in many different shapes and sizes. In this episode, we explore what they are, what benefits they provide, and how the first of its kind study was conducted to see how much of the United States seafloor is covered by these artificial reefs. Our guests today are Avery Paxton, Research Marine Biologist with NOAA’s National Centers for Coastal Ocean Science or NCCOS, D’amy Steward, NOAA Sea Grant Knauss Fellow, and Chris Taylor, Research Ecologist with NCCOS. We dive right into our discussion as D’Amy tells us what an artificial reef is.

STEWARD: An artificial reef is essentially a structure that is placed in the water with the purpose of enhancing fishery resources either for commercial or recreational purposes. It can also serve to help habitat restoration or coastal protection and disturbance mitigation.

HOST: What kinds of structures are typically used as artificial reefs?

STEWARD: Artificial reefs can take a variety of different forms ranging from a design human-made structure which can include a designed reef ball or tetrahedron to mimic natural habitats to also natural structures which can include rocks or oyster shell. We can also use repurposed materials such as a concrete bridge, a culvert, a ship, a train box car, or even power transmission poles. I think the most surprising item for me is a chicken transport cage.

HOST: Wow, I definitely wouldn't expect that to be an artificial reef. So you'd mention they can be either natural or human-made structures. Are there any organizations or groups that create these reefs also?

STEWARD: There are quite a few different groups working to create these structures. I know quite a few. Avery, if you have any you would like to highlight, I'll let you pop in here.

PAXTON: Sure, so oftentimes these structures are acquired by and sunk to the ocean floor by state management agencies. So in North Carolina, for example, some of our colleagues, it's part of their job to acquire these structures from various sources whether they be concrete pipes like D’amy mentioned that have been repurposed from their original use and are now

suitable to be deployed to the ocean floor to form these artificial reefs. And there's also lots of private groups who are at the cutting edge of designing these structures so that they can be most similar to the naturally occurring reefs, for example.

HOST: Are artificial reefs generally pre-planned by humans or can they be created through other intentional ways?

TAYLOR: I think most often they're pre-planned. Like Avery mentioned in the previous question, several groups, whether it be public groups, non-profits, the general public can provide opinions about what sort of reefs they want created. And that's usually then overseen and executed by the state agencies. But the state agencies often also work with regulatory and permitting groups to be able to use the sea floor in a particular way, like deploying an artificial reef. In most of our U.S. waters, that's the U.S. Army Corps of Engineers. And so the organizations like the state agencies will work with the Army Corps of Engineers to permit the space that's going to be used. And then the state agencies will typically acquire the materials, prepare the materials for deployment, and then put them in the permitted area.

HOST: How did these artificial reefs benefit the local ecosystems? And Chris, I’d like to throw that to you first and then have Avery follow up.

TAYLOR: They enhance and benefit the local ecosystem in a number of ways. From benefiting humans, they can potentially increase the access to fishery resources in the coastal environment. And so these fishery resources, meaning they provide habitat that attract or produce fish, and then commercial and recreational fishermen can access those areas.

And they can be placed in spots that may not have previously had a particular habitat that supported that fish community, but can be placed in close proximity to a port or inlet, and can provide ready access for fishers in that case. They can also serve diving communities. Sometimes these habitats are very elaborate in their structure, and in some ways mimic elaborate coral and tropical reefs. And so they can host a diverse array of fishes, and that can attract divers for just sightseeing purposes or ecotourism. And they also affect the types of habitats that are on the seafloor and can serve to enhance the habitats where those habitats may be lacking or may be damaged from other human uses or from other impacts.

PAXTON: So I want to, I guess, elaborate a little bit more on the type of marine life that we often find around these artificial reefs. And I'm going to share some of our observations from an artificial reef created by a ship. The ship was cleaned, and it was intentionally sunk to the seafloor to form a spot for recreational fishing, as well as the diving community to use. And if we were to go down there, as we have with some of our marine robots, for example, or our scientific diving team, oftentimes we see an incredible diversity of fish. We'll see these large bait balls of small silvery fish moving in concert together, and those are often corralled by the large predatory fast swimming fish on the sites. In many cases, we'll see large predators like sharks that are also there. And our team's research has shown that these artificial reefs can be beneficial for these large predators, and even some of the smaller reef fish. And while there are many benefits, there are also risks that we need to be careful with. So for example, in some areas of the world, artificial reefs have been shown to help with the spread of invasive species. And so there's opportunities for the scientific and management community to come together to try to minimize those risks while maximizing the benefits for marine life.

HOST: That's definitely a lot to consider then with artificial reefs. You had mentioned, and Chris had also touched on, recreation and tourism. Chris, could you provide a little more info on how the artificial reefs benefit the local economies?

TAYLOR: I think we see them benefiting the local economies in three major ways. One, providing access to fishing habitat and fisheries, to provide a resource for divers and the diving community to visit, and that's supporting the ecotourism. And then the secondary aspect of that is that those divers are typically supporting dive shops. They're supporting charter boats. Same with the recreational fishers. So you can imagine the secondary impacts to the economy, where they're supporting the fishing shops and the bait shops that are in the area and the dive shops that are in the area. So that's a direct impact to the communities that are in close proximity to those artificial reefs. They also can have an impact on the resiliency of our coastline. So where an artificial reef is created in order to stabilize a shoreline or to protect a shoreline, that can have an impact on the local economy by preserving the natural habitats that provide ecosystem services or support for the ecosystems in that environment.

HOST: One of the things I really wanted to get into in our discussion today is about the study that your team conducted. So Avery, could you tell us about how you, your team, and NOAA partners worked on a study where it was calculated the physical footprint or the extent of these

artificial reef structures on the United States sea floor? How did the study come about?

PAXTON: So Marissa, that's a question that I'm really excited to answer because this study grew from D’amy’s undergraduate thesis, which she conducted while she was an undergraduate at Duke University. And for D’amy’s thesis, she was focused on trying to understand how the seafloor area covered by artificial structures differed from that of the naturally occurring rocky reefs. And D’amy successfully completed that along with our team. And we had momentum and we wanted to understand how much seafloor in the U.S. is covered by artificial reefs across the nation. And so this was a very, very collaborative effort where we worked with partners from 17 different states, coastal states, who have programs where they go out and deploy artificial reefs to help enhance fish habitat and provide these recreational opportunities for community members. And so from that collaboration, we were able to work with all of these states to develop a common system for us to estimate how much seafloor is covered by these structures.

HOST: D’amy, can you tell us more about the physical footprint itself?

STEWARD: So our team calculated that the footprint of artificial reefs in the U.S. coastal ocean to be approximately 20 kilometers squared. That's equivalent to 3,600 American football fields, and that's almost seven square miles of artificial reef on the seafloor. And when we look at a permanent area on the reef or on the seafloor, this is the amount of seafloor where these structures can be deployed. The total area is approximately 5,800 kilometers squared, which is nearly the area of the state of Delaware. The additional space that is not currently occupied by materials allows for natural spacing of these structures to create new habitat, but also provide natural areas for foraging.

HOST: Chris, my next question is for you. Are there specific areas in the U.S. seafloor where there are a majority of these artificial reefs, where they can be found?

TAYLOR: The artificial reefs are placed on the seafloor for a variety of purposes. Often if they're deployed for fishing and for ecotourism and diving and for enhancing offshore habitat, they're going to be in relatively close proximity to inlets or access points, piers, docks, ramps, boat ramps, and they're going to be readily accessible by the fishing community, by ecotourism. They're generally in shallow water in that case, and I'm going to pass it over to D’amy because she has some really good statistics on where these artificial reefs may be found relative to the states and the coastal states in particular.

STEWARD: Yeah, thank you, Chris. So coming in at number one with the most artificial reef coverage, we have Texas at 7.82 kilometers squared, followed by New Jersey with 4.44 kilometers squared, and then our third most coverage we have for Florida at 2.3 kilometers squared. Those are our top three in terms of percent cover and area covered of artificial reefs for U.S. states.

HOST: So the coverage with those areas, was there anything surprising with those findings or is this kind of expected?

PAXTON: So I'll take that. So I was very surprised actually with the results from this study. So I thought that the amount of seafloor covered by artificial reefs in total was going to be higher. So 3,600 American football fields, that's such a small drop in the bucket, especially compared to the ecological impacts that these structures can have. So I would probably say that artificial reefs can have an outsized ecological impact for their footprint on the ocean. So that was surprising to me. The other thing that was surprising to me was the diversity of different types of structures and materials that have been put on the ocean floor for artificial reefs. D’amy mentioned this earlier, but chicken transport cages, for example, telephone poles, tires were used multiple decades ago and ended up being too mobile and moved in storms and washed up on beaches. But ships, train box cars, planes, etc, military vehicles have all been put on the seafloor. And Chris, what about you? What was the most surprising thing to you in this study?

TAYLOR: I was surprised at the variety of ways that states manage their artificial reefs and how they maintain the information and database for understanding what's out there in their artificial reefs and then for the various involvement of user groups in the deployment of those artificial reefs. I think the statistics that D’amy just voiced were maybe the most surprising. Texas, the big state of Texas, led the way with the most and the greatest footprint of artificial reefs, but followed by New Jersey, which has one of the smaller coastlines on the Atlantic seaboard. And then Florida, which is a massive shoreline exposed to both the Atlantic and the Gulf Coast, came up as a distant third. That surprised me a bit. It also surprised me how challenging it was for D’amy and Avery, who gathered up the majority of this information with artificial reef managers, how challenging it was to actually find out what was on the seabed or still on the seabed. And the long history of deploying artificial reefs has not been maintained or it's been maintained in a variety of ways by the states. And so gathering up all the information took a variety of approaches. And the study that D’amy and Avery led here is quite intensive in devising a variety of ways to make those estimates of the footprint of artificial reefs on the seafloor.

HOST: How did you actually calculate the reefs themselves? How did you pull the data?

PAXTON: So I'll start with that one. So the calculations, we thought, were going to be relatively simple, Marissa. We thought we were going to be able to go out and work with the states and understand exactly what objects had been deployed, how big those objects were, and thus what area of the seafloor they covered. Turns out that that worked for many structures, but not all. So for some structures, we had this measured footprint. We had estimates of the length and width, for example, of train box cars that had been deployed or concrete pipes that had been deployed. But for other structures, we did not have those measured values. And so our team had to come up with a way to estimate those missing values as footprints. And D’amy do you want to share a little bit about how we did that?

STEWARD: Sure. So we were able to create essentially a classification system. We had general categories that we could assign because there's such a variety, as you've heard, of structures. We formed these broad categories and we could assign a range of sizes to them. And by doing so, we were then able to group all of these structures from across the U.S. into various categories to help facilitate this calculation for the structures where maybe we didn't know how much area of the seafloor covered. It really allowed us to figure out some of the unknowns and apply estimates to structures we otherwise would not be able to calculate.

PAXTON: And an example there would be there's all sorts of different concrete modules that have been deployed. So you may have modules that are built out of concrete that are triangular, trapezoidal shaped. You may have some that are dome shaped. You may have some that are cube shaped. And we were able to group all of those into a category for concrete modules and use the information about the concrete modules whose footprints we knew to inform what that estimate should be for the others that we didn't have that information for. So it was an iterative process and it was informed by the data that we had, I think is the key there as well.

HOST: It's so interesting to hear again about the diversity of the different types of structures that are used to create these reefs. I know we'd previously touched on the challenges with the reefs. Someone had mentioned about an invasive species can sometimes be attracted to certain structures which can cause problems with the ecosystem. Avery, I wanted to ask you, are there any risks associated with in particular human-made reefs?

PAXTON: There are risks associated with human-made reefs from the ecological perspective. So one of those we already mentioned and you just reviewed is that they can help spread invasive species. I think at a kind of broader level than that though is that sometimes these artificial reefs can function ecologically in a very different way than some of their natural reef counterparts and because of that it may lead to unintended ecological patterns and processes. So an example of that could be that in many cases, there's this debate over whether if you put an artificial reef down, you will see fish very quickly, but those fish are probably coming from a nearby natural reef, and so there's a kind of cost benefit analysis that goes into that, and ideally what you want is you want fish to be able to be produced or more new biomass of fish at these sites which could help offset some of that loss, maybe, of fish moving from a nearby habitat to your artificial reef when it's installed. And then Chris do you want to add any more on that in terms of other ecological risks associated with artificial reefs?

TAYLOR: Yeah I think we mentioned some of the materials that were deployed previously that were thought to be a good idea like tires. If they become overly mobile they can wash up on beaches and their mobility, their movement across the seafloor, can potentially damage other habitats and that's something that I think the artificial reef managers are paying much more close attention to these days. They're looking at the materials, they're making sure that they're preparing the materials, cleaning the materials before their deployment so they're not having that direct and immediate impact, negative impact to the environment.

PAXTON: So to me the most important thing from this study is that because we drew upon the best available records of artificial reefs from 17 states and had such a high level of teamwork and collaborations with different state agencies, we were able to calculate the first nationally coordinated calculation of the artificial reef footprint in the U.S. ocean. And so to me that piece in and of itself is pivotal because before this project started, we didn't have that information in a standardized national format and so now we can use that information to try to improve our understanding of how these artificial reefs, which are dotting the seafloor nationally, function ecologically. And I think I'll pass it to Chris maybe to talk a little bit more about that ecological function piece.

TAYLOR: Now that we have that number right we have a number that seems much smaller than we than I think anyone expected. It gives us sort of a scale and a magnitude to understand how like how many fish could these habitats hold in each of their regions, how many species could these different material types hold and then sort of understanding the quantity of magnitude of how many fish are on these habitats and how many they they might produce to contribute to the sustainable ecosystem, which can lead towards management which can lead towards conservation which can lead towards measures of understanding how you optimize the types of materials that you put out there and where you put them. We just lacked that basic information of quantity and distribution that would help us do a better job in the future of managing the ecosystems through deployment of things like artificial reefs.

STEWARD: Now that we have this national number with the categorization that we use to be able to work across state boundaries, I think we've kind of established a collaboration across states so we can continue to add to this national calculation and continue to improve it and refine it, but also as we introduce more artificial structures in the future, we can update this number, and I think it's an exciting step that we now have that number, but now it leaves us with so much room to grow and continue to collaborate across state boundaries and have this national number. I think it's a really exciting future.

HOST: To wrap up our discussion today, I’d like to go around and have our guests share any final thoughts.

PAXTON: I know we've talked about the diversity of different types of structures that have formed artificial reefs, and we've given lots of examples, but I wanted to share a few more examples. So there's missile platforms, there's cables, there's vehicles like we already talked about and then one of the structures I was not expecting was voting machines. In some situations, voting machines have actually been reefed to form these artificial habitats.

TAYLOR: I think this study overall just surprised us in a number of ways that the types of materials, the creative reuse of human-made materials and how they were deployed, some of those materials were maybe a good idea and some of them maybe could use some rethinking but just understanding the quantity of those materials on the seabed helps us understand the contributions of habitats and the substrates towards the functioning of the ecosystems, and I think that's a good this study sort of as a baseline it helped us sort of quantify

these things and develop these sort of magnitudes of and relationships between the habitat types and the communities and ecosystems that they support.

STEWARD: I just want to say this was an amazing collaborative effort both within NOAA, across state boundaries, it really was a team effort and I think we're really fortunate to have such an amazing group of scientists working together and everyone was really passionate and excited you know it really was a labor of love to you know start in the southeast and say you know what let's cover the entire U.S. coastline this just in a really impressive group of people and I just feel very fortunate to have been a part of this and just a huge shout out to everyone who is involved both within NOAA and again across state boundaries and everyone came together and I think we have a great product.

HOST: This has been the NOAA Ocean Podcast. Thanks for listening and check out our show notes to learn more about artificial reefs. Be sure to catch all our episodes in your podcast player of choice.

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