A mollusc shell pathway in Isle of Mull, Scotland. Credit: James Morris

Across the world, hundreds of millions of people rely on the ocean for their food and livelihood. In 2013, this meant that about 180 million tons of seafood was caught and produced globally, the weight of nearly 500 empire state buildings. Unsurprisingly, this consumption level comes at massive a cost: Not only is it depleting our ocean’s fish stocks, but also creating huge amounts of waste. Every year, millions of tons of crab, shrimp, lobster, and mollusc shells end up in landfills or get dumped into the sea. But now, a team of researchers from the Royal Belgian Institute of Natural Sciences (RBINS) are searching for a way to turn this seafood trash into sustainable treasure.

“Mollusc shells are viewed by the aquaculture and seafood industries as ‘nuisance waste’ and largely disposed of in landfills,” explained Dr. James Morris, from the RBINS, in a press release. “Not only is this an expensive and ecologically harmful practice, it is a colossal waste of potentially useful biomaterials.”

Advertisement

Morris and his team believe that given mollusc shells’ chemical makeup, they could easily be recycled for industry use rather than discarded in landfills. Mollusc shells are composed of over 95% calcium carbonate, a compound which is used in a variety of industries, including agriculture, construction, and engineering; calcium carbonate’s uses include improving soil health, treating wastewater, and producing cement. Currently, the majority of the world’s calcium carbonate comes from marble and limestone, both of which require mining and refining before they’re ready for industry use in ubiquitous products like cement.

However, according to the RBINS, over 7 million tons of mollusc shells are discarded by the seafood industry each year. This readily available source of calcium carbonate could be a gold mine. According to Nature, the market price of ground calcium carbonate is over $65 per ton; this means that if mollusc shells were refined to ground calcium carbonate, they could be worth tens of millions of dollars. “Reusing shell waste is a perfect example of a circular economy, particularly as shells are a valuable biomaterial,” explained Morris. “Not only does it improve the sustainability of the aquaculture industry moving forwards, but it can also provide secondary economic benefits to shellfish growers and processors as well.”

Advertisement

Morris and his team are part of the CACHE, an organization focused on bringing together experts in ocean conservation and young researchers and PhDs, with the goal of training the next generation of scientists. Another of the organization’s core missions is to increase understanding of calcium production in marine environments and better predict the impact that climate change will have on marine and freshwater ecosystems.

Advertisement

Morris has also been exploring the use of discarded shells to help restore damaged oyster reefs, which would serve the dual purpose of reducing waste and protecting important ecosystems. If discarded shells are placed in reef areas, oyster larvae, known as spat, will often stick to them, and use these old shells as their permanent home. As time passes, if the reef is well managed it can grow in size and become self-sustaining. “Healthy shellfish populations can have many benefits to the environment: cleaning the water, providing a complex structure for other organisms to call home, and also acting as a coastal protection structure,” explained Morris. There have already been a handful of successful oyster reef rehabilitation projects at the local level across the U.S. that have relied on discarded mollusc shells.

An artificial oyster reef in the Netherlands. Credit: James Morris

While Morris’ work is concentrated on mollusc shells, there’s equal need to find sustainable uses for other marine waste; according to Nature, crustacean shells are 20–40% protein, 20–50% calcium carbonate and 15–40% chitin, all substances which could be repurposed.

“The proper disposal procedure for shell waste is in landfill, which costs a lot of money and can be a big burden for shellfish farmers and seafood producers,” said Morris. “Simply finding a use for shells to avoid taking them to a landfill already has economic value!”