Article: Burns JHR, Delparte D, Gates RD, Takabayashi M (2015) Integrating structure-from-motion photogrammetry with geospacial software as a novel technique for quantifying 3D ecological characteristics of coral reefs. PeerJ 3:e1077
What is 3D printing and how is it used to study coral reefs?
The 3D printer has proved to be a wonderful machine, printing things from primitive body tissues, to car parts, and even printing cool designer shoes! Three-dimensional printing was birthed in engineering fields, but new technology has taken 3D printing to a whole new level, printing replicas of the most ecologically and economically productive structures on the planet—coral reefs. The goal of printing a coral reef is to accurately evaluate coral growth in order to better understand how these diverse ecosystems respond to human and environmental stressors such as climate change and fishing.
The complex architecture of coral reefs is composed of calcium carbonate structures that provide diverse microhabitats ranging from intricate cave systems, to tiny crevices that only the smallest invertebrates can inhabit. The overall shape and topographic complexity of coral colonies drive key processes like photosynthesis and reproduction. Recent advances in both computer technology and photogrammetry make 3D models cost and time effective. Using the new low cost structure-from-motion (SfM) 3D reconstruction technology, Burns et al. set off to quantify the structural complexity of coral reefs.
Building the 3D model and how it proved useful
For the baseline coral reef, images were collected at the French Frigate Shoals (Fig. 1). Divers swam in a grid pattern of 25 by 6 meters, continuously photographing the benthic substrate during a 60-minute dive. Using these images 3D models were constructed using a modeling software. The spatial properties of coral configurations within the given coral reef were then quantified. Together these steps (Fig 2) produced a 3D structure of the actual coral reef from the French Frigate Shoals. Through this model, researchers were able to analyze a variety of key features going into coral reefs that would normally be extremely difficult to observe underwater. Some features that were examined and proved useful in building our knowledge were:
– Surface contour of the coral reef (rugosity) – As corals grow in height, the rugosity of the coral reefs grows more complex. Therefore, as a general rule of thumb, the higher (more complex) the rugosity, the more available habitat there is for the colonization of benthic organisms, shelter, and foraging area for mobile fishes.
– Percent coverage of coral – this shows how much coral is growing on the benthic substrate, if it’s growing in more of a vertical pattern or more outward, and how much of the reef is taken up by coral compared to open cave spaces.
– Coral growth– in order to understand the growth pattern of corals, it helps to know how they grow. By analyzing individual growth and size patterns of corals within the reef, a better understanding of coral growth can be made.
The researchers found that plating and branching corals had the most complex growth pattern, finding that as these corals grow vertically they tend to be more convex, while horizontal growth proved to be concave. The combination of both concave and convex growth patterns plays a role in creating more microhabitats, which leads to more species diversity and richness.
Using this new cost effective model of photogrammetry and software to build a 3D model provides an accurate, and useful, method of analyzing the structural complexity of coral reef ecosystems. The way corals grow with each other proves to be an important predictor of the diversity of fish and invertebrate species found on the reefs. Through 3D models, scientists can really analyze the growth patterns of corals without interfering with the natural habitat of the coral reef ecosystem. Key coral species that contribute to reef diversity can also be identified with the 3D model. This will help researchers understand the effects environmental perturbations have on the coral reefs. Future research can combine the 3D models with other ecological parameters to improve our knowledge and capacity to monitor changes in coral reef health.