Advanced virtual technology captures how coral reefs recover after bleaching

Researchers at the Scripps Institution of Oceanography and engineers at UC San Diego have used new imaging software to detect dramatic recovery after bleaching on the reefs surrounding the remote Palmyra Atoll in the tropical Pacific. The research was published on April 5 in Coral reefs.

In 2015, Palmyra experienced the warmest waters in its history, causing widespread bleaching that affected more than 90% of the corals surrounding the island. The researchers found that despite widespread bleaching, most corals recovered with less than 10% of deaths.

The findings are based on a comprehensive monitoring of the reefs and provide more precise observations on the evolution of these reefs over time. The researchers used a long-term dataset of thousands of images of the same reef area collected over an eight-year period. These images were assembled with the help of custom software to create 3D photo mosaics of the ecosystem, a virtual representation of corals. The technology was developed by the 100 Island Challenge team, a collaborative group of marine ecologists and engineers using the latest technologies to monitor coral reefs around the world.

"This imagery provides a way to get back into the environment in a virtual world," said Mike Fox, senior author and postdoctoral fellow at the Woods Hole Oceanographic Institution, who did the research as a PhD. student at Scripps. "This allows us to bring the reef back to the laboratory."

The researchers combined this imaging technology with a new custom visualization software, VisCore, which allows users to re-examine the thousands of photographs that make up the mosaics. VisCore took more than 15,000 images for each coral reef area of ​​10 square meters, then processed the data to turn it into a 3D map in which users can immerse themselves in virtual reality.

The 100 Island Challenge literally opened up another dimension to Viscore by bringing together a highly interdisciplinary research team to create the data, algorithms and tools that now allow scientists to virtually explore the reefs in the lab; travel in time virtually from year to year; monitor the growth and decline of individual colonies; and study spatial and temporal relationships across the reef.

The project was made possible by the merger of Scripps researchers and the Jacobs School of Engineering at the University of San Diego, said Falko Kuester, professor of computer science and structural engineering at the University of San Diego .

"We want to give voice to coral reefs, tell their stories and engage stakeholders to protect them," he said.

Hundreds of videos generated by researchers are available on YouTube for public viewing.

"The program gave us the unique opportunity to virtually review each of our dives and examine the reef from a new angle," Fox said. "When we went back into the images, we realized that the bleaching was even worse than we remembered when we were diving on the reef to collect the data."

In addition to documenting bleaching, researchers were able to closely monitor the recovery of coral. After looking at the photomosaics of the reef after bleaching, Fox and his team have documented the growth of an important species behind the construction of the reef, the crustal coralline algae. This algae contributes to the cohesion of the reefs and can promote the colonization of juvenile corals.

In areas where the coral is dead and covered with seaweed smothering the reef, the researchers found that in about a year this seaweed had been replaced by pink coral. This is partly due to the health of the larger ecosystem, as Palmyra has large populations of herbivorous fish capable of controlling the destructive growth of algae.

Tracking these recovery processes in specific coral colonies over time gives researchers a better understanding of how individual corals – and the wider reef they are part of – are coping with environmental stresses at the same time. era of climate change influenced by man.

Traditionally, changes in coral reefs were measured with transect sampling, during which divers noted observations along a specific line across the reef.

"It's like trying to measure national population growth by going to a random American city and asking people if they had a child," said Scripps researcher Stuart Sandin, who co-authored the paper. and co-founder of the 100 Island Challenge. "You're not going to show the bigger picture."

With reef mosaics and the precision of the VisCore system, coral scientists can look at demographic clues in a vast area. The specific nature of the data colonies gives more precision and, just as monitoring the population growth of a country, can show regional and national trends.

"By combining innovative technology and more traditional approaches, our team has been able to demonstrate that Palmyra's reefs have not suffered the same fate as many other reefs during the recent global bleaching event," he said. said Jen Smith, Scripps researcher. author on paper and co-founder of the 100 Island Challenge. "Despite extreme warming, corals have been able to recover without widespread mortality, and these results are certainly an important counterpoint to the global decline in reef health globally."