Written by Danielle Moloney
In September, I reported about the devastating effects that hurricanes have on coral reefs for Reefbites. Dr. Rogers (2019) documented the havoc that hurricanes and other natural disasters can have on reefs, but what can be done in their wake to study reef ecosystems and interactions without the need to use corals directly? Scientists came up with a creative solution to forming experimental reef models – 3D printing coral models to stand in their place.
As early as summer 2018, Alex Goad (at the Reef Design Lab, in 2018) had created and installed a 220-piece 3D printed coral reef structure in the Indian Ocean, close to an existing coral nursery, in order to assess the success of this potential solution for reef habitat recovery. While this was a long anticipated project, skepticism has risen over the feasibility of 3D printing as a legitimate solution to mass coral degradation. Understanding how a foreign material will affect the behavior of corals (i.e settlement rates) and their associated organisms (i.e damselfish activity) is crucial to conservational 3D reef printing. As reefs are delicately balanced ecosystems, a change in the status-quo can have wide reaching impacts habitat-wide. At the University of Delaware, Dr. Danielle Dixson and Emily Ruhl (M.S) analyzed how 3D printed corals affect the behavior of damselfish and the rate of settling stony coral larvae. These two types of organisms were chosen to serve as an indicator of whether or not reef inhabitants on a greater scale would react differently to 3D printed structures vs. natural corals (Ruhl & Dixson 2019).
Dixson and Ruhl used blue green damselfish (native to the Indian and Pacific Oceans) and mustard hill coral larvae (a stony settling coral native to the Caribbean Sea) as proxies for how fish and corals may behave in the wild in the presence of a 3D printed coral structure.
In order to create a 3D model, photos were taken from 50 different angles of a coral skeleton and digitally stitched together to form a model. The model was then 3D printed by building layers of melted material incrementally from the base upward (Image 1). Researchers chose two scleractinian coral species, Acropora formosa and Pocillopora damicornis, for their morphological divergences to rule that out as a possible confounding variable (Figure 1). Four artificial models of each coral species were printed to assess the viability of different materials based on cost, weight, and effectiveness: two polyester structures and two biodegradable structures. The biodegradable material used was cornstarch, and one of the two structures was mixed with stainless steel shavings.
Dixson and Ruhl placed the damselfish and coral larvae in a tank with native coral skeleton and a 3D printed skeleton and measured their preference for either habitat. They analyzed the distance and frequency of movement for the fish (i.e activity level) as well as the rate of settlement for the coral larvae.
Results and Implications
Interestingly, the results of this experiment indicated that damselfish showed no preference or change in behavior when exposed to artificial coral substrates vs. natural coral skeletons. Conversely, the coral larvae exhibited significantly higher levels of settlement in aquaria with 3D printed coral as opposed to control aquaria that lacked any substrate.
These findings have broad implications for the future of reef conservation. Coral reefs are already struggling with degradation, so rather than performing invasive experiments on remaining healthy corals, 3D models can be used for some studies as a proxy for the real deal. Many studies on fish behavior and other aquatic measures can be standardized by using 3D models of coral to ensure the exact same color, dimensions, etc. of the coral used in the experiment. Given the success of damselfish and coral larvae in this experiment, 3D modelling for reef recovery is a promising option that research may delve into further. However, this research does have drawbacks. Aspects of 3D printing such as the effect of material used (especially plastics) are of concern, as well as the effect on the ecosystem as a whole, are cause for concern and further study.
Future studies may assess the potential for 3D coral models as a long term solution for reef recovery after emergencies such as hurricane destruction. They may also examine the implication of adding 3D coral models on other species known to inhabit coral reefs, such as algae, to predict the success of the ecosystem more holistically. Furthermore, data on the impact of the building material used to create 3D models should be measured as a potential disruption to reef systems. In the future, Ruhl & Dixson may further their experiments by testing the same measures in a tank with a 3D printed coral vs. a tank with natural coral material, rather than a tank lacking any substrate.
While 3D printing is an innovative new technology for reef research, it cannot act alone as a solution. Larger issues that plague reefs such as climate change and human impact cannot be solved with this technology, so the continuation of coral reef research, with the addition of 3D printing as a unique solution for only certain reefs where it has been thoroughly researched, is imperative.
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