Coral reefs are highly productive ecosystems that have come under threat in recent decades as a consequence of climate change. This has fueled a surge in research on the basic biology of corals with a view to restoring reefs that have been damaged by ocean heating and acidification. Reef restoration depends on the successful recruitment of juvenile corals and this is difficult to quantify using current 3D modeling techniques because the juveniles are so very small and cryptic.
This problem has led marine biologist Dr. Kate Quigley to develop a new method for monitoring coral size and growth that relies on the use of dental scanning equipment. Digital 3D scanning is commonly used in dentistry and implant manufacturing because measurements need to be accurate right down to the μm scale in order to produce highly accurate molds. Intraoral dental scanners are also safe to use on live tissue, whereas previous 3D modeling methods often involved destroying the corals in order to measure them.
Dr. Quigley, a senior research scientist at the Minderoo Foundation, has published details of the new method in the journal Methods in Ecology and Evolution. She was inspired to develop the new scanning method by a visit to her dentist.
During her visit, Dr. Quigley remarked on the similarities between coral and human teeth – both being calcium-based and requiring measuring tools that can withstand wet surfaces. “One day, I was at the dentist, and they rolled out this new scanning machine. I knew immediately that it was something that could apply to scanning very small corals given that corals and teeth actually share many similar properties. The rest is history!”
Although the older technologies involved in 3D modeling of coral reefs have seen substantial improvement and development in the recent past, they are really only applicable to objects in the size range of meters to centimeters. They lack capability in the millimeter and micron (μm) size range, which is what is necessary when measuring the early life stages of corals. Understanding the critical life stage of juvenile coral allows scientists to predict ecosystem changes, the impacts of disturbance and the potential for reefs to recover.
“At the moment, it is difficult to accurately measure very small objects in 3D, especially if you are interested in measuring small live animals, like coral, without hurting them. During my PhD it would take half a day to produce one scan, and I was interested in scanning hundreds of corals at a time,” said Dr. Quigley.
To assess the effectiveness of these dental scanners, namely the ITero Element 5D Flex, Dr. Quigley measured juvenile corals from different species and size classes. The corals were originally collected from the Great Barrier Reef Marine Park and included species with complex branching morphology, as well as those with simple branching and those that have a flatter, encrusting life form. The trial was conducted at the National Sea Simulator at the Australian Institute of Marine Science, where the corals were temporarily removed from their indoor aquarium to have their surface areas and volumes scanned.
On average it took less than three minutes to scan and build a model of each individual coral compared to over four hours with previous methods – a 99 percent decrease in the time required to carry out such measurements. Dr. Quigley recorded equally fast and precise performances when measuring and comparing models of dead skeletons and living coral tissue, thus removing the need to sacrifice live animals in order to take measurements.
“For the first time, this new method will allow scientists to measure thousands of tiny corals fast, accurately and without any negative health impacts on the coral. This has the potential to expand large-scale monitoring of ocean health and for up-scaling coral reef restoration.”
While this is a huge improvement in terms of cutting down the time involved to monitor these small marine animals, the technology can only be used to make measurements out of the water. The scanning instrument is not waterproof and it relies on the use of lasers. In addition, the 3D scans still need to be processed manually, which is a slow process. Dr. Quigley hopes to create an automatic analysis pipeline from scanning to measurement in future, potentially using AI.
“Potentially the scanner could be made completely waterproof. However, it is unclear how well the laser technology would work completely submerged underwater. We have taken this technology on the boat before and brought up wild and laboratory-reared corals for measurement, so we are getting there!”
“The pairing of both rapid data acquisition and processing in this way has the potential to significantly improve our understanding of coral biology for pressing questions around conservation in this important biological system.”