Tracking deep-sea coral health after Deepwater Horizon oil spill
Paramuricea biscaya coral hosting multiple associates, including a brittle star, aplacophoran molluscs and anemones, at a depth of 1,400m. Credit: NOAA, Oceaneering International, Inc.
Fifteen years after the devastating Deepwater Horizon oil spill poured an estimated 134 million gallons of oil into the marine environment, vital long-term monitoring work involving University of Hawai‘i (UH) at Mānoa oceanographers continues to chart the slow path to recovery for the region’s deep-sea coral communities, providing critical information to guide their restoration. These marine organisms, living at depths of 1,000 to 2,000 meters, were directly impacted by the largest offshore oil spill in U.S. history.
In mid-October, two oceanographers from the UH Mānoa School of Ocean and Earth Science and Technology participated in the latest expedition aboard the R/V Point Sur that was revisiting monitoring sites off the coast of Louisiana. The team’s mission was to capture new images of more than 200 individual coral colonies using a remotely-operated vehicle (ROV) equipped with high-resolution still and video cameras.
“Processes in the deep ocean are very slow,” observed Fanny Girard, assistant professor of oceanography at SOEST and lead investigator in the project. “Many of these animals look exactly the same as they did in 2011. It’s a sobering reminder that recovery in the deep sea takes time.”
High-tech imaging and painstaking analysis
The monitoring project, which began immediately following the discovery of impacted coral communities, represents the longest existing time-series for deep-sea corals globally. The first phase (2011 to 2017) of this work aimed to evaluate impacts to deep-sea corals to inform the Natural Resource Damage Assessment process. Following the 2016 settlement with BP Exploration & Production, the second phase of this work is now informing restoration by providing critical baseline information on coral health, growth and role as habitat for many other species.
To ensure consistency in this long-term restoration effort, the researchers employ a meticulous process to document growth rates and overall health, including changes in individual coral polyps. At the monitoring sites, they previously deployed physical markers— dive weights and floats with reflective tape—to find the exact same coral colonies and guarantee replication of high-resolution images year after year. Once the images are collected by expert ROV pilots, Girard and her graduate student Jack Howell manually compare new photos to past images, a demanding process that can take hours for a single coral colony.
“We compare the past coral images to what we’re seeing now to be sure that the new photos match the exact coral and alignment,” explained Girard. “This photo comparison is done by hand by two researchers to reduce error and ensure accuracy, and we annotate any changes.”
To accelerate this traditionally time consuming analysis, the researchers are currently developing a machine learning model to help automate the tedious process of health status assessment. This innovation will be a boon not just for this project but for other efforts to monitor deep-sea health.
Coral and brittle stars
While monitoring the corals, the researchers have made important discoveries about the health of the ecosystem.
“We’ve learned that lots of animals, particularly brittle stars, live on these corals,” said Howell, whose project is focused on associations between coral and other organisms. “This seems to be a ‘win-win’ collaboration, where the brittle star may receive food and shelter, while the coral benefits from the brittle star potentially eating parasites and cleaning up sediment that could compromise its health.”
Ultimately, the data gathered through this project—which links coral health to environmental conditions—is vital for the next steps in restoration. The expedition’s recent focus on reference sites that were not impacted by the spill will be key to setting a crucial biological and environmental baseline for future restoration success.
Project details
Funded through the 2016 settlement with BP Exploration & Production, Girard’s research provides critical data for the ongoing Mesophotic and Deep Benthic Communities restoration efforts. Led by NOAA and the Department of Interior alongside many federal, academic, and nonprofit partners, this portfolio executes many days at sea each year to complete crucial field work to inform and conduct restoration activities. Partners on this expedition included USGS, University of Rhode Island (including the Ocean Exploration Cooperative Institute and Inner Space Center), University of Southern Mississippi, and Smithsonian National Museum of Natural History.
Read also on UH News and Environmental News Network.