The Impact of Artificial Reefs on the Marine Ecosystem
This topic submitted by Matthew Friend (
friendmj@muohio.edu) at 10:59 PM on 5/15/09.
A swim in a tropical stream, Corcovado Natl Park.
Matthew Friend
GLG 413
Dr. Hays Cummins
The Impact of Artificial Reefs on the Marine Ecosystem
An artificial reef is defined as a man-made, underwater structure, typically built for the purpose of promoting marine life in areas of generally featureless bottom. The use of artificial reefs today has become a popular method in which to save the reef dwelling species throughout the world whose natural habitats are threatened due to human impacts by pollution and the introduction of foreign species to an area not previously inhabited by that species, which causes an adverse effect to the reef, also known as an invasive species. Artificial reefs are made up of numerous materials, including concrete, steel, and even old worn out tires. Around the world, reefs are built out of old used materials that would otherwise sit in a junkyard, or garbage dump. The use of artificial reefs to protect marine species has been in action for numerous years and shows no evidence of slowing. It has become a way in which we, as humans, can build a structure to help marine species as well as control the erosion of beaches, create recreational dive sites, and also produce waves acceptable for surfing. Artificial reefs have become a major staple to recreational diving, fishing, and habitat restoration; Florida has become a leader in the development and implementation of artificial reefs in order to cope with the current losses of natural reefs due to the impact of humans.
Florida has been a major proponent in the construction and use of artificial reefs in order to develop dive sites for recreational divers as well as professionals and fishermen. Some sites are made up of concrete, while others are made up of old tires, such as the Osborne Reef near Fort Lauderdale, which has become a major topic of debate currently due to the unplanned release of tires into the water which drift away and no longer serve a positive purpose. This reef was made up of over two-million tires, and as a result of displaced tires, a large scale removal plan has been put into effect in order to prevent further degradation of corals both in the Osborne Reef and surrounding reefs (Morley et al. 2008). Florida has become a leading figure in the use of artificial reefs and has created the Florida Sea Grant Connection in which further research has been funded in order to look into whether artificial reefs are a positive option for habitat restoration. William Seamen and Aaron Hoover published an article for the Florida Sea Grant Connection in which they discussed some of these projects and their overall result, most of which turned out to result in a positive manner in which the populations of crabs, algae, fish, etc. benefited from the construction of a reef (Seamen & Hoover 2001). Due to FloridaÕs location in the United States, it is most vulnerable to large storms and hurricanes which can cause the movement of some artificial reefs due to increased wave sizes and movement. As a result, the locations of some reefs are no longer current, so researches have come up with the idea in connection with the Florida Sea Grant Extension to potentially locate and map artificial reefs which have moved with the use of low frequency side scan sonar (Jackson et al. 2007). This proved to be an outstanding method for locating the current position of reefs, not only for marine census purposes, but also for recreational divers and fishermen. Other reefs around Florida and the Florida Keys are made by the scuttling of old, decommissioned, naval vessels which are towed out to their reef destination and sunk. One such ship is the USS Oriskany which was scuttled south of Pensacola, Florida and has become the largest artificial reef on record. It lies in 210 feet of water, but the top island is accessible to recreational divers at 70 feet. There are numerous other reefs around Florida constructed from the use of old, naval vessels, some of which have actually been used as research projects in which very low electrical currents have been passed through the steel in order to build up limestone on the steel allowing for the attachment and growth of coral planulae, young coral. This technique has been termed Biorock Process, which is currently being used for reef restoration, mariculture, along with shore protection.
Although Florida possessed numerous reef structures made up of old, naval vessels and tires, the majority of artificial reefs are made from concrete. This is not always the most preferred material for algae growth, so researchers have begun looking into the use of chemical attractants, or chemoattractants, in order to lure algae to the reef and encourage growth. They looked into five different chemoattractants, ferrous sulfate, zinc oxide, ammonium nitrate, sodium phosphate and ferrous lactate and found that concrete coated with ferrous lactate lured and promoted the most growth compared to all the others (Lee et al. 2008). Also, combinations of the mineral treatments were used, resulting in other positive effects but none as great at the ferrous lactate treatment.
Not only does the use of chemoattractants determine how many or what kind of microorganisms colonize a new reef, but also the overall composition of the reef determines how the reef will develop and what it will house. In a study, Fukunaga et al. looked into how two different artificial reefs in Mamala Bay, Oahu, Hawaii were colonized by polychaete species and how these compared to a natural reef of similar size and composition. One of the artificial reefs, named Sea Tiger, allowed for the colonization of polychaetes similar to that of the natural reef called 100Õ. The other artificial reef, YO257 was not colonized by the polychaetes in such large numbers as the other two reefs, but attracted many more crustaceans. They determined that the colonization of the two artificial reefs was due to the other marine fauna colonizing, and also the sheer composition of the rocks in which the polychaetes came into contact. The rock of the reef Sea Tiger allowed for the drilling and boring of the polychaetes, while that of the reef YO257 did not, thus causing the drastic changes in polychaete numbers and allowing for more crustaceans (Fukunaga et al. 2008).
The colonization of reefs is not the only concern of researches looking into whether artificial reefs are a positive method for attempting to conserve the marine habitats of today. Scientists have also begun to look into how reefs made by man affect the feeding habitats of fish in an area not previously exposed to an artificial reef, simulating the construction of a reef in that particular area. One particular study looked into the grazing habits of algae-preying fish in an area not previously exposed to a reef. The scientists built a reef and released algae at various distances from it in order to observe the grazing habits of the algae feeders. Their results show the construction of a reef does, in fact, cause an increase in fish grazing habits, and the reef created a zone of increased grazing where fish were then localized to a specific distance around it. They could then potentially weigh the risks of grazing too far from the protection of the reef to how exposed and vulnerable they were to predation (Einbinder et al. 2006). The larger the reef complex, the more complicated the increase in the grazing habits, number of grazers, and biomass the reef was responsible for. A similar study was performed in which reef sizes were varied and fish censuses were taken over a two year period. The results showed the larger the reef size, the greater the fish abundance and species richness (Jordan et al. 2005).
The size of a reef complex can determine the species of fish housed within, but the overall complexity of the reef can also determine the number of different species the reef can house. In a 2006 study, Perkol-Finkel et al, found that the more complex an artificial reef, the higher the number of coral and invertebrates who settle on and colonize the reef. Going along with other research, the scientists also found that the face chemistry, toxicity, and stability of the reef materials correlated with the number of species on the reef. A reef that is more stable will, in turn, house a greater diversity of species due to the decreased chances of the reef structures breaking off and potentially injuring or destroying other coral structures. The researchers concluded in their study that the structural features of an artificial reef are more responsible for determining the species that colonize rather than just the age of the reef itself.
Going along with reef substrate and complexity, current research has been performed looking into whether such objects such as offshore windmill farms could not only serve a purpose as a renewable energy source, but also as artificial reefs. The footings of the windmills could potentially allow for an increase in fish protection, as well as an increase in species diversity of organisms in an area due to an increased surface area. Much research still must be performed before there is a conclusion to the question as to whether offshore windmill farms can allow for increase marine diversity in an area, but whether positive or negative, these effects are yet to be determined (Peterson & Malm 2006).
The use of old, dredged material in the restoration New York-New Jersey Harbor has also been a topic of reef research. These materials have been deemed unsuitable for deposition to outside ocean estuaries, and current research into the project has shown both advantages and disadvantages. One advantage, due to artificial reef and berm construction, includes increased fish populations in the harbor leading to an increase in fish harvesting. A disadvantage to this plan is small scale research much first be performed before large scale operations were to proceed. Reefs would have to be built on a case-by-case basis due to the degree of difference in the bottom composition throughout the harbor (Yozzo et al).
In conclusion, artificial reefs have been shown to be a positive method for enhancing, renovating, and constructing new habitat for species threatened by the loss of their natural reefs. Artificial reefs are currently still being studied as to their longevity and how they will work in the years to come, however most research has shown that with the correct materials and, in some instances, the correct chemoattractants, marine life can find, colonize, and live in man-made structures meant to mimic an organismÕs natural habitat. With all of the coral bleaching and destruction of reefs throughout the world, something must be done to either halt reef destruction or replace current reefs in order to house the fish living within and throughout. Artificial reefs have shown to be one of the best alternatives. Man can destroy natural reefs, but man can also create a new and similar habitat just as fast, and artificial reefs so far have shown to be the answer to this ongoing issue.
Literature Cited:
ÒArtificial Reefs of the Florida KeysÓ 8 February 2002. Allen J (2000). Artificial biospheres and a model for Global ecology on plant Earth. Life Support Biosphere Science, 7(3) 273-282.
Einbinder S, Perelberg A, Ben-Shaprut O, Foucart MH, Shashar N (2006). Effects of artificial reefs on fish grazing in their vicinity: Evidence from algae presentation experiments. Marine Environmental Research, 61 110-119.
Fukunaga A, Bailey-Brock JH (2008). Benthic infaunal communities around two artificial reefs in Mamela Bay, Oahu, Hawaii. Marine Environmental Research, 65 250-265.
Jackson S.L., Parsons G.H., Davis G., Crosby K (2008). Assessment of nearshore artificial reefs in Okaloosa County, Florida by volunteers using side scan sonar. American Fisheries Society 191-200.
Jordan L., Gilliam D.S., Spieler R.E. (2005). Reef fish assemblage structure affected by small-scale spacing and size variations of artificial patch reefs. Journal of Experimental Marine Biology and Ecology, 362 (2) 170-186.
Lee HS, Sidharthan M, Shim CS, Kim YD, Lim CY, Ko JW, Han MD, Rang MJ, Bim LS, Cho HS, Shin HW (2008). Screening and formulation of chemoattractant coatings for artificial reef structures. Journal of Environmental Biology, 29(4) 605-612.
Morley D.M., Sherman R.L., Jordan L.K.B. Banks K.W., Quinn T.P., Spieler R.E. (2008). Environmental enhancement gone awry; characterization of an artificial reef constructed from waste vehicle tires. Wit Press (Environmental Problems in Coastal Regions VII) 73-87.
Perkol-Finkel S, Shashar N, Benayahu Y (2006). Can artificial reefs mimic natural reef communities? The roles of structural features and age. Marine Environmental Research, 61 121-135.
Peterson JK, Malm T (2006). Offshore Windmill farms: threats to or possibilities for the marine environment. Ambio, 35(2) 75-80.
Seaman W, Hoover A (2001). Artificial Reefs. The Florida Sea Grant Connection. Sea Grant Florida. www.flseagrant.org
Yozzo D.J., Wilber P., Will R.J. (2004). Beneficial use of dredged material for habitat creation, enhancement, and restoration in New York-New Jersey Harbor. Journal of Environmental Management 73 39-52.
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