Investigating the influence of additional structural complexity in present day reef restoration
Date
2020
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
Coral reefs are degrading at an alarming rate, with reefs transitioning from topographically complex, species rich systems to topographically poor, species impoverished communities. One technique in combating reef degradation is through coral outplanting. Traditionally, this method uses fragments of healthy corals and transplants them to grow in a location where coral coverage is low. However, this method can lead to lack of genetic diversity and low survivorship of certain species, due to less than ideal growth conditions (i.e. light, nutrient load and water flow). Another restoration method is the inclusion of artificial structures into reef systems; while these structures provide additional substrate, the space provided is not ecologically similar to the reef they are replacing. Here, combining the techniques behind coral outplanting and artificial structures, I implemented a novel outplanting method that harnesses modern 3D-print technology, to enhance coral reef recovery through increased structural complexity. 3D-printed corals, designed from a Pocillopora damicornis skeleton, were deployed in Fiji via a patch reef system of cement plates. The system was organized into matrices (n=3) of different 3D-corals and live coral densities to determine how 3D-structures can serve as temporary habitat for coral reef organisms during reef recovery. I aimed to understand how coral reef fishes utilize patch reefs containing a mixture of 3D-printed and living corals over time. By measuring fish abundance, species richness, diversity, and fish behavior on the patch reefs over 12 months, I observed that increased artificial complexity enhanced reef fish community composition. After a year, the 50%, 75%, and 100% 3D-coral treatments had comparable fish species abundance, species richness and diversity to the natural reef. The 3D-coral patch reef treatments attracted 135% more herbivores than the natural reef, and 400% more fish used the 3D-corals as feeding grounds rather than swimming and using the artificial structures as habitat. Additionally, this design allowed me to observe the interaction between living corals and the 3D-printed material, to assess the ability of the 3D-corals to integrate into the natural reef. By measuring coral growth, color, and survivorship, I determined the maximum effectiveness of the 3D-corals while limiting the number of artificial structures placed in the natural system. I determined that all treatments containing a combination of living and 3D-printed corals (25%, 50%, and 75%) were able to successfully integrate into the living reef. None of the treatments inhibited coral growth or caused coral bleaching; coral mortality and bleaching were determinate on the species of living coral, rather than the percentage of 3D-coral. Focusing on the protection and rehabilitation of the reef ecosystem through progressive conservation methods, this study allows for an accurate assessment that utilizing 3D-printed corals is a safe and effective restoration technique that provides realistic reef habitat to complement natural reef processes
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Keywords
3D-printing, Artificial reefs, Coral reef, Outplanting, Reef fish, Restoration