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In Puerto Rico, discarded beer bottles could be a key to saving corals

As the climate crisis has worsened over the years, marine scientists have been ringing alarm bells about trash polluting the waters. We’re well on the way to the point when there will be more plastic than fish in the ocean, microplastics are filling up marine animal stomachs, and activists are constantly working on ocean cleanup efforts. So, at first glance, it may seem strange that one group of researchers is actively putting garbage back into the sea. But for the past two years, Isla Mar Research Expeditions and HJR Reefscaping have been working on a project in Puerto Rico that involves turning recycled beer bottles into sand, incorporating that sand into a cement mixture, and using itto plant corals to revive suffering Caribbean reefs.

Coral reefs around the world are under extreme duress, largely due to human-caused climate change and everything that comes with it: pollution, sedimentation and runoff from coastal developments, water acidification, rising surface temperatures, and increasingly frequent and intense storms. The latter is a serious concern in Puerto Rico, where hurricane season all but promises devastation — on land and underwater. When Hurricanes Maria and Irma hit Puerto Rico in 2017, for example, they harmed already vulnerable coral reefs around the Caribbean islands. As the Associated Press reported, hundreds of thousands of corals snapped off of their reefs during Maria alone.

And as is the case with most climate change-related destruction, the devastation from hurricanes compounds. Coral reefs serve as a crucial first line of defense for coastal environments. “That three-dimensional structure breaks up the wave energy and helps reduce flooding, which in turn keeps the shoreline in place and prevents erosion from washing foundations out from under buildings,” says Chelsea Harms-Tuohy, Ph.D., who co-founded Isla Mar Research Expeditions with her husband and fellow marine biologist and scientific diver, Evan Tuohy, Ph.D. candidate. “Even if you live further inland, you're counting on the buildings and structures close to the shore to serve that purpose for your own home, thus a healthy coral reef protects all of us.” In other words, it’s a vicious cycle: Hurricanes damage reefs, then weakened reefs allow hurricanes to (further) damage the land beyond the reefs, and so it goes, year after year.


And, Harms-Tuohy notes, “That's just the structural component. A healthy coral reef also supports our health and wellbeing as humans — it supports the protein sources we eat, like lobsters and fish, and provides sources for medicine.”

Meanwhile, on land, Puerto Rico (like the rest of the U.S.) lacks sufficient infrastructure for recycling, particularly glass. Most bottles pile up in landfills unless they can be put to a better use. Enter: The Medalla Light restoration initiative. The idea came to Evan Tuohy while he was enjoying a post-work beer, as so many great ideas do. The couple had recently seen a social media video about a bottle crushing machine that turns glass bottles into sand, created by a company in New Zealand. “That inspired us to ask the question, ‘Can we use crushed sand in our cement mixture to plant corals to the reef?’” Harms-Tuohy says. “It seemed like the perfect way to upcycle a piece of waste — and glass waste is a major issue for our island.”

They had already been working with HJR Reefscaping to plant coral fragments in the sea using a cement mixture containing crushed marble (known as marmolina) and seawater — one of several methods used by scientists for coral restoration. So, the team got to work researching the components of crushed glass sand to determine if it would be safe and effective for coral planting. Then they reached out to Medalla Light’s parent company, local brewery Cervecera de Puerto Rico, to explain the project and ask where their beer bottles were made.

It was a crucial question. “Since we were approaching this from a scientific perspective, we knew that these were factors we needed to be in control of,” Harms-Tuohy says. “We needed the sand to come from the Caribbean, so that we knew it would be composed of silica from our area — an essential element used by marine organisms to build their skeletons and shells. … Medalla Light bottles were our ticket to controlling the sand composition in the cement mixture.”

Not only did the Medalla Light bottle manufacturer confirm the Caribbean origins of its bottles, but the brewery also agreed to fund the project, covering costs including purchasing the bottle crushing machine and promoting the conservation message throughout Puerto Rico.

Isla Mar officially launched the project in June 2021, creating cement mixtures with varying amounts of recycled glass sand (RGS) so they can ultimately determine the best ratio for a healthy reef. While there are several coral species in the Caribbean, the scientists are using Elkhorn coral for this project. Not only is it “one of the largest and fastest growing corals in the Caribbean,” Harms-Tuohy notes, but it’s also “capable of asexual reproduction called fragmentation, where it can essentially clone itself when a fragment or branch breaks off, cement itself to the substrate, and then start growing a new coral right there.” The research team collected the fragments from damaged reefs (caused by things like storms, boat groundings, and trash), as well as human-built coral nurseries, to use in their restorations.

Once they had all the components, Harms-Tuohy and her team planted the fragments on both degraded and thriving reefs where Elkhorn already exists (or previously existed). “Sometimes the fragments are planted on top of dead coral structure, scattered around a larger area, or they can be planted in small groups to encourage growth of a larger three-dimensional reef unit,” Harms-Tuohy says, noting she and the other marine scientists take into account the presence of faster-growing things like algae and sponges that “compete with corals for space.” The goal is to give the coral the best chance to thrive and survive, and not get overtaken by other species before it can do so.

Of course, new corals still face the same risks as existing or ruined ones — and unfortunately in this case, the majority of the fragments Isla Mar and HJR planted last year suffered from coral bleaching. “Coral bleaching is a coral's stress response,” Harms-Tuohy says. “This can happen from waters that are too warm for too long, or from other stressors like poor water quality and sedimentation that smothers a coral's ability to receive sunlight.” The increasing presence of those stressors, scientists agree, is a direct result of human-caused climate change.

While all is not lost — Harms-Tuohy says they’re monitoring how well the bleached corals respond and recover, and even if they don’t make it, they could still serve as a natural substrate for new corals to grow — this was certainly a setback. After waiting a few months for the proper season, the team replanted 300 additional fragments in early 2022 to make up for it.


Despite the stumble, though, Harms-Tuohy says the project is going well; the RGS doesn’t seem to be negatively affecting coral growth, and they’ve even unexpectedly discovered that they can replace all of the marmolina in the cement mixture with the RGS. “It’s great, because now we can purchase fewer supplies and instead increase our use of this glass ‘waste’ product,” she says.

This initiative is just the start. Not only did Medalla Light agree to fund an additional year, but “we have [also] been working behind the scenes to try and brainstorm bigger ways that we can recycle or crush this glass and use the end product for worthwhile purposes on this island,” Harms-Tuohy says. “We have other marine conservation uses, but we are trying to think even more broadly to come up with creative ways that we can use RGS.”

And then there are the less tangible wins. “Once [Medalla Light] helped get this message in the spotlight, we started receiving all kinds of messages from people wanting to know where they could donate their bottles or where they could recycle them,” Harms-Tuohy says. “It was great to see so many people that really cared about this message as much as we do.”

That said, just like there’s no easy fix for climate change, this isn’t a fail-proof savior for suffering corals — and it’s certainly not a permission slip to continue polluting. “Restoration is an action in response to destruction, and we cannot rely on this to fix our problems in the ocean. Positive change must go beyond just buying a reusable bottle and saying no to plastic,” Harms-Tuohy says. “Behaviors and mindsets of whole governments — local and national — must change. We have to start looking at our oceans as a finite resource that will disappear if we don't take care of them. We have to pressure our leaders to enact the change that you as an individual are committed to making, but we need that on a much larger scale. We need to value our fishery resources enough to let them have a break from our constant take. We need to respect the regulations that are put in place to protect our marine life and watersheds.”

Put simply: “We just need to be responsible humans and realize we are sharing this planet.”


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