Artificial reefs

University of Applied Sciences Van Hall Larenstein and Wageningen University and Research recently conducted a comparative study of artificial reefs within the Caribbean. This study provides new insights into the impacts of these structures on local marine life and neighboring ecosystems and highlight the need for comprehensive monitoring and integration into marine management plans. 

Photo credit: Rudy Van Geldere

Since the 1960s, artificial reefs have been placed around the Caribbean for tourism, to aid in improving fish stock, providing coastal protection and for scientific research. Unfortunately, there has been limited research to fully understand these reefs’ impact or compare artificial reefs to their natural neighbors. Researchers debate whether artificial reefs actually improve fish populations by encouraging increased reproduction or whether they are merely attracting fish from nearby reefs. Understanding how artificial reefs affect local fish populations and neighboring reefs will be critical in implementing meaningful conservation strategies in the future.  

 The Study 

 A new study conducted by University of Applied Sciences Van Hall Larenstein and Wageningen University and Research within the AROSSTA (Artificial Reefs on Saba and Statia, www.hvhl.nl/arossta) project aimed to evaluate the ecological effects of artificial reefs within the Caribbean. To do so, 212 different artificial reefs were analyzed based on reef type, location, deployment year, purpose, material, ecological development and fisheries management status.  

 The Results 

The results proved very insightful. It was determined that the three most common purposes for artificial reefs were to serve as new dive sites (41%), for research (22%) and to support ecosystem restoration (18%). In addition, they found metal and concrete to be the most widely used materials. They also found a number of factors which could help bolster fish populations, such as reefs which more complex geometries and those placed in areas of dense seagrass. 

This study also found that of all the artificial reefs, only 38 are located within marine protected areas which prohibit fishing. This means that over 80% of all artificial reefs are fishable. This is especially true for the Southern and Southwestern Caribbean Including Aruba, Bonaire and Curacao) where 100% of the reefs are within legal fishing zones. As artificial reefs attract part of their marine organisms from surrounding habitats, intensive exploitation by fishers can adversely affect the fish stocks in the surrounding area and thus counteract any potential ecosystem benefits. 

Photo credit: Mark Vermeij

Future Conservation

Effective marine conservation will require additional information on the impacts of artificial reefs on these local environments. The benefits of increased fish biodiversity and populations could be quickly undone by overfishing within the same area. The authors therefore conclude that the current management status of most artificial reefs in the Caribbean is a threat for its fish stocks. If implemented properly, artificial reefs could be a critical tool for future conservation efforts. Therefore, this study concluded that artificial reefs should be carefully monitored and integrated into future marine management plans.  

To find out more, you can read the full study  by clicking the DCBD link below.

https://www.dcbd.nl/document/artificial-reefs-caribbean-need-comprehensi...

Article published in BioNews 46

Manmade structures such as seawalls, breakwaters, and jetties are increasing in frequency in marine coastal environments. Overtime, these structures are unintentionally recruiting marine life such as corals, resulting in the formation of artificial reefs. A recent study in the Caribbean has revealed how the biodiversity on these artificial structures compares to natural reefs.

Coral reefs are visually very aesthetic, but above all they play a central role in the ocean. Coral reefs support over 800,000 marine species and supply numerous ecosystem goods and services. Yet sadly, corals are threatened by a combination of global climate change and local human activities such as fishing, shipping and coastal development. Natural recovery is too slow, so active restoration efforts are crucial to prevent the loss of our coral reefs.

CORALS UNDER THREAT

One method of coral reef restoration is the construction of artificial reefs. Artificial reefs come in various forms. Some are designed and deployed specifically to enhance marine life. Others, such as shipwrecks and urban structures –including jetties, seawalls and breakwaters– recruit marine life unintentionally. With increasing coastal development, the frequency of urban structures in the marine environment is increasing, yet marine communities on urban structures receive less attention in scientific research.

This old artificial reef was visibly manmade with smooth basalt blocks cemented together (Source: Naturalis Biodiversity Center)

Filling this gap, a team of researchers explored the biodiversity of urban structures at St. Eustatius, an island of the Caribbean Netherlands. Their findings are published in the scientific journal Marine Pollution Bulletin. The team consists of Claudia Hill from the University of Groningen and Myrsini Lymperaki from the University of Amsterdam, under the supervision of professor Bert Hoeksema, who is affiliated with Naturalis Biodiversity Center and the University of Groningen.

A NEW HOME FOR MARINE LIFE

The island of St. Eustatius, popularly known as ‘Statia’, is located in the eastern Caribbean and is a special municipality of the Netherlands. The island is steeped in history, having changed hands between numerous European empires and having thrived as a port of trade in the 17th and 18th century. Today St. Eustatius is much quieter, though traces of the past like remnants of ancient piers and jetties remain in the coastal water. “These ancient structures shelter a new home for marine life”, tells Claudia Hill, first author of the article. “With corals and other benthos living on the remains, altogether forming an artificial reef”, she continues.

This natural reef was partly biogenic and located on top of a rough lava underground. It supplied a variety of microhabitats in the form of crevices and overhangs.

ARTIFICIAL VERSUS NATURAL REEF

The research team compared the biodiversity on the artificial reef to that of a natural reef nearby. “We found a considerably higher biodiversity on the natural reef, with a wider range of species, a higher density of organisms, and different dominating species”, explains Hill. “We concluded by the greatly differing communities on each reef that artificial reefs can not serve as surrogates for natural reefs.” The researchers highlight, however, that the main cause for biodiversity differences lies in the deviant structural features on the reefs. The natural reef exceeds the artificial reef in microhabitats like crevices and overhangs that are beneficial to the growth of marine life.

What I personally found most surprising, is despite the artificial reef being centuries old, the cover and abundance of reef organisms is still not comparable to that on the natural reef.  But it is important to note, that whilst the artificial reef did not host an identical community to the natural reef, it still serves as a healthy and diverse reef in its own right.

-Claudia Hill

Therefore, there is still a place for artificial reefs in conservation work, as they serve to enhance the marine life of the local area. “Artificial reefs provide a promising outlook for the future of coral reefs, yet a precautionary approach must be taken to prevent any unwanted consequences, such as the invasion of non-native species.”

MORE INFORMATION

• Curious about further details of this study? Read the full publication in Marine Pollution Bulletin.
• For further details about the study, please contact Bert Hoeksema and Claudia Hill.

Text: Claudia Hill, University of Groningen, Naturalis Biodiversity Center
Photos: Naturalis Biodiversity Center

https://www.dcbd.nl/document/centuries-old-manmade-reef-caribbean-does-n...

Article published in BioNews 45

Caribbean coral reef ecosystems are threatened by anthropogenic impacts such as pollution, overfishing, and habitat destruction. In an effort to alleviate these pressures and restore habitat, artificial reefs such as marina breakers, Reef Balls, and mooring blocks have been deployed and consequently colonized by marine species. Many studies have investigated the benthic and fish communities developing on these artificial structures as compared to adjacent natural structures. Results have shown that artificial reefs can successfully be colonized by benthic and pelagic communities but are not always comparable to the associated communities. The purpose of this study was to compare the composition of benthic habitat and the use of this habitat by fish between manmade mooring blocks functioning as artificial reefs and natural coral reefs of Bonaire. Quadrats were used to estimate and compare percent cover of benthic organisms on the top and west faces of mooring blocks versus the top and west faces of physically paired natural reef sites (n = 8). An 8 min visual census was conducted on each face of each site pairing to estimate fish abundance and diversity for those species interacting with the habitat. Results showed greater percent live benthic cover on the natural versus artificial reef. Benthic diversity was highest on the west face of the artificial reef when comparing the interaction of face and reef type, but did not differ significantly between reef types. Fish community diversity also did not differ between reef types. However, the composition of both benthic and reef fish community diversity differed greatly between the natural and artificial reefs. It was found that Montastrea annularis and sponges dominate the natural while the brain corals (Diploria labrinthiformis and Diploria strigosa) dominated the artificial reef. Bicolored damselfish (Stegastes partitus) and brown chromis (Chromis multilineata) were found in the highest densities on the natural reef, while sergeant major (Abudefduf saxatilis) and bluehead wrasse (Thalassoma bifasciatum) were found in the highest densities on the artificial reef. This study provides evidence that placement of artificial reefs does not cause a shift in overall benthic and reef fish community diversity on the natural reef, but may change the composition of this diversity.

This student research was retrieved from Physis: Journal of Marine Science VI (Fall 2009)19: 44-52 from CIEE Bonaire.

Nesting animals select sites for reproduction based on adaptive behaviors that have evolved to improve reproductive success and the survival rates of offspring. Abudefduf saxatilis, commonly known as the sergeant major, is a pomacentrid fish that exhibits nesting and nest-guarding behaviors. This study in the coastal waters of Bonaire, Dutch Caribbean, evaluates whether A. saxatilis selects rough or smooth substrates for nesting, and whether there is a vertical relief requirement for the nesting site using a reef survey and a field experiment. Nests on the reef were surveyed to determine if trends exist in the number and area of nests as height and rugosity of substrates increase, and a field experiment was designed to present the fish with a choice between rough or smooth surfaces and between units of varying heights. It was hypothesized that A. saxatilis would lay more and larger nests on smooth substrates with a vertical relief >20cm in both the experimental and reef environments. A trend towards more nests on smoother surfaces was observed in both the block experiment and in the reef survey, but no trends in number or area of nests were consistent between the experiment and the reef survey. Understanding the patterns of nest selection of A. saxatilis will provide important insight into the reproductive success of this highly abundant species, and because availability of nesting sites is a bottom-up control that can influence coral reef trophic structures.

This student research was retrieved from Physis: Journal of Marine Science IX (Spring 2011)19: 12-19 from CIEE Bonaire.

Coral reefs around the world are experiencing high levels of degradation due to temperature changes, increased nutrients and destructive fishing techniques. For example, where there were once large thickets of the branching coral Acropora cervicornis along the coasts of Bonaire, Dutch Caribbean, there is now sand and dead coral. Loss of an entire highly complex habitat has likely altered the local reef fish community. Artificial reefs have been used in the past to test hypotheses about structural complexity and its effects on reef fish communities. However, no studies have sought to discover if artificial reef structures modeled after A. cervicornis would support reef fishes found in the natural branching coral colonies by mimicking the structural complexity provided by the coral. To answer this question, four patches of artificial A. cervicornis were constructed and placed near the reef crest on the leeward side of Bonaire, Dutch Caribbean. Natural thickets of A. cervicornis were used to compare differences in fish species richness, diversity and density. Artificial reef structures were found to support higher diversity but lower abundance of fish. There was no significant difference in species richness between the natural and artificial reef stands. Overall, the artificial reef structures were able to provide some shelter to certain fish species, but were not able to support the fish community that is supported by natural stands of A. cervicornis.

This student research was retrieved from Physis: Journal of Marine Science X (Fall 2011)19: 21-27 from CIEE Bonaire.

The implementation of artificial reefs is one effort used to mitigate the rate of decline of coral reefs and the deterioration of fish communities. Artificial reefs add support to struggling reefs habitats by providing additional or varied structural relief, sometimes mimicking specific coral structure types. The purpose of this study is to assess the effectiveness of branching artificial reef (BAR) habitat deployed in November 2011 by comparing the fish density and biomass, and species richness and diversity of the BAR to those of habitats in which it was placed. Three plots of BAR habitat were compared to three plots of rubble habitat and three plots of fore-reef habitat. BAR plots were found to have significantly lower fish density, fish biomass, and species richness than the fore-reef, but no statistical difference in species diversity. When compared to the rubble, BAR habitat showed significantly higher species richness, but no significant difference in density, biomass, or diversity. A comparison of family and fish phase community composition revealed that BAR habitat supports significantly more initial phase Scaridae than either adjacent habitat. It was concluded that BAR habitat adds little in the way of a complementary habitat to the terrace-fore-reef zone. The results from this study suggest that no further implementation of this form of artificial reef should be carried out along the rubble terraces of Bonaire. However, further monitoring of the BAR habitat and research into a branching structure with greater complexity, more interstitial matrix and constructed from calcareous material may be useful.

This student research was retrieved from Physis: Journal of Marine Science XI (Fall 2012)19: 88-95 from CIEE Bonaire.

Artificial reefs are commonly used to increase habitat space for reef-dwelling organisms. Coral reefs in Bonaire, Dutch Caribbean, are degrading due to factors such as disease, bleaching events, and heavy storms, reducing habitat space for reef fish. Two different artificial reefs were deployed on the leeward side of Bonaire in 2011: one block and one branching structure. Studies found that both reefs supported fish communities but utilization of the reefs by fish was not studied. The current study examines utilization of branching and block-style artificial reefs for foraging and feeding activities by herbivores and predators to assess which reef structure provides more resources for fish. Herbivore grazing and predator stalking rates were calculated as well as herbivory and predation pressure at increasing distances away from the artificial reef. The branching artificial reef supported more herbivore and predator activity compared to the block reef, suggesting structural complexity increases important sheltering and feeding areas for reef fish. Predation and herbivory pressures showed no trend with increasing distance from the artificial reef while predation pressure decreased with increasing distances from the natural reef. This suggests that the artificial reef may act as a shelter between the reef crest and the surrounding sand and rubble area, thereby increasing foraging distances of fish coming from the reef crest. Not only resident, but transient individuals, were found to use the artificial reefs for feeding and sheltering, suggesting that artificial reefs do not need to create permanent habitats in order to be important habitat for reef fish.

This student research was retrieved from Physis: Journal of Marine Science XI (Fall 2012)19: 46-57 from CIEE Bonaire.

Coral reefs are important marine ecosystems with high biodiversity that provides food and socioeconomic benefits to people in tropical regions around the world. In the last thirty years coral cover has declined and has been wiped out in some areas. The coral loss affects all benthic organisms and fishes supported by these habitats. Artificial reefs have been used to enhance coral recruitment and to provide a habitat for reef fishes. In Bonaire, Dutch Caribbean, reef fish species richness, diversity, and density were measured at two types of artificial reefs, branching and block-style, at various times of the day. Field observations of reef-fish species richness and density were conducted at midday, dusk, and night. Branching artificial reefs supported higher species richness and diversity. Multiple herbivorous species utilized this habitat for grazing while other species used it for shelter. The block-style reefs supported a higher density (ind m -2 ) of reef fish. Fish density, species richness, and diversity decreased at night at the branching reef. The decrease in fish community complexity could be because the complexity of the block-style reef was not suitable for nighttime sheltering needs. Species richness and diversity also decreased at night at the block-style reefs; but density at night was no different than midday and dusk because the blocks supported a very high number of small individuals during nighttime. Two different artificial reef structures were found to support complex fish assemblages; however the species richness and fish abundance varied between the structures. This suggests that morphology of artificial reefs is a tool that can be utilized to attract specific reef fish communities. During a time of reef degradation and habitat loss, artificial reefs can be used to supply reef fish a habitat to live. 

This student research was retrieved from Physis: Journal of Marine Science XI (Fall 2012)19: 35-45 from CIEE Bonaire.

Reef fishes and invertebrates are quickly losing their habitats due to widespread coral degradation. Artificial reefs are entering the spotlight as alternatives to this problem because they provide marine life with habitats. The role that artificial reefs will play in marine resource management is still unknown, partly because artificial reefs are often overlooked as alternatives due to a lack of knowledge about them. Without the right information on artificial reef placement, the reefs may be used inefficiently. This study focused on how reef fish assemblages and invertebrate coverage can be influenced by artificial reef isolation, distance from the natural reef. This study was conducted in Bonaire, Dutch Caribbean, at the Yellow Sub dive site. Six mooring blocks were visually censused for fish biodiversity and photographed to find percent invertebrate coverage. Three of the blocks were weakly isolated and the other three were strongly isolated from the natural reef. The study took place over a five-week span from September through October 2012. The only significant difference between the weakly and strongly isolated blocks was that there was higher fish abundance on the weakly isolated blocks. Fish biodiversity and percent invertebrate cover did not differ significantly between the two block isolations. A better understanding of what factors allow for more suitable habitats on artificial reefs will contribute to conservation efforts and could increase reef fish and invertebrate biodiversity and abundance.

This student research was retrieved from Physis: Journal of Marine Science XII (Fall 2012)19: 64-72 from CIEE Bonaire.

Increasing coral reef degradation worldwide is putting more reef fish under stressful circumstances. A possible solution to mitigating the effects of degraded coral reefs is the implementation of artificial reefs. An ongoing question of effective artificial reef utilization asks how far from a natural coral reef ecosystem should these structures be placed. Some studies support the theory that structure isolation attracts larger fish diversity in terms of aggregation and recruitment. In order to test such a hypothesis, four identical artificial structures were deployed next to a coral reef ecosystem in Bonaire, Dutch Caribbean. The impact of position relative to the natural reef was measured, placing two structures close to the reef crest and two 30 meters inshore on the sand flat. After conducting fish counts over a five week period, it was found that artificial reef isolation attracted a higher assemblage of fish, particularly juveniles. Total fish assemblage counted for 1021 fish at the sand flat and 364 fish at the reef crest, with higher fish diversity at the reef crest (1 - 0.77 = 0.23). An interesting temporal trend of French Grunt recruitment was observed at the sand flat. These results demonstrate fish preference for isolated artificial reefs, but the range of species recruited may be limited.

This student research was retrieved from Physis: Journal of Marine Science XIX (Spring 2016)19: 9-15 from CIEE Bonaire.