Oysters are a delicacy for some, a staple food for others, but they are also vital to coastal ecosystems. They cling to each other and stack like stalagmites growing from the ocean floor. Over time, the hardened oyster shells form vast reefs that resemble underwater cities. They provide habitat for many aquatic species, filter water and improve its quality, and cushion waves caused by storms and shipping, protecting shorelines from erosion.

Dr. Jonathan Wilker, a chemistry professor at Purdue University, studies how oysters and other marine animals create their underwater bonds. While many marine animals produce “protein glue,” Wilker says oyster cement is unique because—in addition to a small amount of mostly proteinaceous organic matter—it contains a large amount of inorganic calcium carbonate.

Strategy

Calcium carbonate, otherwise known as limestone, is not a glue at all. So how does oyster cement work? Much like skyscrapers need to be rigid and flexible to allow them to sway slightly in the wind (without tipping over), oysters combine hard calcium carbonate with softer, sticky proteins, allowing them to withstand the strong forces of the tide while holding their colonies together. In 2010, Wilker demonstrated that the protein molecules “crosslink,” meaning they form a kind of mesh or spider web that binds all the ingredients together and gives the cement its stickiness.

Imagine a brick wall, where mortar (acting as organic matter) bonds the brick to both the other and other surfaces, while the bricks (acting as calcium carbonate) add strength and rigidity. While an actual brick wall follows a regular pattern, the structure of oyster cement is far from uniform.

Wilker's research continues to unravel the complexities of the binding material. For example, unlike oyster shells themselves, oyster cement uses two types of calcium carbonate, chemically equivalent but made of crystals of different shapes and orientations.

Other results suggest that the glue may contain material from the aquatic environment and may even include a symbiosis of bacteria that add sugar to the organic part.

Options

One of Wilker’s goals is simply to understand how nature makes materials. That’s exciting enough in itself. But he points out that this research has a range of potential medical applications, including bone repair and dental prosthetics, which involve bonding inorganic materials in moist environments. In addition, this work is leading to a sustainability mindset that could be used to build human-friendly structures along the coast—and help restore the 85 million oyster reefs that have disappeared around the world in the past century due to human activity.

Visit us on social media (Facebook, Instagram)

Summarized by AskNature.org