Scientists testing a new method of coral restoration they have called ‘rubble stabilisation’ are celebrating an early win in the coastal waters of Hawai’i this week after an area left severely damaged by a ship running aground some 12 years ago has shown ‘positive early signs’ of a bounce back.

Through a process that involves securing loose, broken parts of the reef to the seafloor to give corals a stable surface to grow, scientists from the National Oceanic and Atmospheric Administration are hopeful they will be able to foster live coral growth by deploying a pioneering method and getting hands-on in this first-of-its-kind coral reef DIY project.

The origins of this restoration effort date back to 2022 when divers from NOAA and the State of Hawai’i discovered that the coral habitat at the site of a ship grounding some 12 years prior was not recovering in the way they had expected.

One of the main issues was that sections of the reef were still covered by loose rubble.

It was in 2010 that the M/V Vogetrader cargo ship ran aground, damaging almost 3,500 square metres of vibrant coral reef – an important habitat for fish and other marine species. An initial damage assessment documented the loss of an estimated 100,000 coral colonies.

It turned out that the ship’s hull had gouged and disintegrated the reef framework itself into what was described as a ‘field of rubble’. Three years on and in 2013, habitat restoration commenced with the removal of 354 square-metres of rubble and the outplanting of 643 coral colonies. 

It was hoped this would be enough to kickstart a natural recovery process that “wouldn’t require future intervention.”

Almost a decade on from the ship grounding, however, and studies revealed that only 45% of the outplanted coral colonies had survived. What’s more, a significant amount of rubble remained, rolling and tumbling across the seafloor impacting the survival rates of baby corals recruiting to the site.

Coral reefs are critical to life across Hawai’i. Fish rely on healthy coral reefs for food and shelter, while native Hawaiian communities rely on a healthy fish population. They also rely on the coastal protection coral reefs provide as they absorb wave energy and buffer shorelines from damage and threats to human life during storms and floods.

To address the issue, NOAA Fisheries and experts from the Cooperative Institute for Marine and Atmospheric Research set out to find a solution for the site’s biggest issue: the rubble. 

Borrowing an emerging technique observed in other ship grounding coral restoration projects, namely those successfully deployed in Puerto Rico, marine habitat resource specialist Shannon Ruseborn adapted the approach for the rougher, Hawaiian waters.

In Puerto Rico, the method had returned some positive results. After the process, 14% of the reef was covered by live coral. It has also increased the reef ruggedness index by more than 100 per cent.

“It seems simple: loose, tumbling live rocks are secured to the seafloor, creating stable surfaces for coral to grow,” said Ruseborn. “But the waters of Hawai’i are rougher than tropical reefs. Whether it could even be done was an open question.”

In partnership with the Coral Restoration Foundation, workshops were held to educate NOAA staff on the new method which included learning how to install boulder pipes and testing different ways of attaching mesh to the seafloor.

“The decline of our reef’s 3D structure – either through events such as mass bleaching or ship groundings – will continue to threaten our reef communities. I think manual rubble stabilisation has exciting potential to give these degraded reefs a leg up on recovery,” said Courtney Couch, a coral reef researcher at NOAA.

“That said, no one method is going to work for all reefs. So we are extremely fortunate to have the opportunity to bring experts together during our recent workshop to discuss and test different approaches together. We couldn’t have begun this process without the training.”

Over the course of the three-week mission, the researchers had established methods across 20 sites: ten sites had installed mesh plots while another ten had built cemented boulder piles. A final ten sites were identified as control sites.

The team will head back to the site in spring this year to check how secure the sites are after Hawai’i’s winter swells. If they remain intact, the team plans on partnering with Kuleana Coral Restoration to outplant corals onto the mesh and boulder piles.

The hope is these outplanted corals will grow and add more stability to the plots. From this point, they will monitor the sites every six months.

“This will help us figure out whether new corals are settling and surviving and what tweaks to make in the future to ensure its success,” said Ruseborn.

“After the last few years and all of our efforts that got us to this point, it’s going to be hard to wait until the spring to see what’s happening down there. I am excited that we’re trying something new. The project will determine if this can be a tool in the restoration toolbox in Hawai’i. We’re all going to remain cautiously optimistic that we can help bring this reef back to life.”

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