Project
SeaCrete: Bio-inspired and bio-sourced alternative for concrete in marine ecological recovery
Biogenic reefs, hard structures formed by living organisms such as e.g. corals, oysters, mussels and tubeworms, provide vital components of healthy marine systems worldwide. The North Sea historically was rich in oyster-dominated reefs, which have been fully removed by over a century of overharvesting and recurrent seafloor destruction by trawling. The same happened situation occurs with tropical reefs.
These extremely biodiverse and productive habitats form the basis for local livelihoods and coastal protection, in many places however, they are destroyed by destructive fishing practices and coastal developments. This means loss of multiple ecosystem services such as settlement substrate for seafloor flora and fauna, food supply, shelter, spawning grounds, and water filtration, thereby enhancing biodiversity and supporting fishery conditions. Given their high economic and ecological importance, restoration of reefs is extremely urgent. Current efforts to kick-start reef restoration mostly involve introduction of large amounts of concrete artificial reef materials where the corals and shellfish can settle on.
However, concrete has several disadvantages: it has
a large CO2 footprint, requires extensive amounts of sand, and is considered an unnatural material by several people. In nature, oyster and coral reefs continuously develop on older biogenic reef materials. Ideally, old oyster shells and dead coral rubble should be reused as filler, if only they could be mechanically held together for several years underwater until new organisms had the opportunity to develop on them into a robust natural reef. Current underwater adhesives, however, are based on reactive two-part epoxide chemistry that is unnatural, expensive, and harmful, while also being very easy to use. Recycling of wasted empty shells or coral rubble would be ideal to kick start reef rehabilitation if they could be glued together using a biocompatible, underwater adhesive.
For this problem, nature offers a possible clever solution: The sandcastle worm, P. californica, produces an underwater adhesive by combining positively and negatively charged polypeptides for fast adhesion underwater. Applying small quantities of this ‘glue’ to bind nature-sources reef material together would form the natural structure required for nature-based habitat rehabilitation.
SeaCrete is a combination of a coacervate adhesive that binds together oyster cultch, coral rubble or any other desired material. It is a paste-like material that can be molded into different shapes for specific applications (see photos), and upon submersion in sea water because a solid, elastic material that lasts for months, to potentially years on the sea floor. Several properties of Seacrete are easily tuned: elasticity can be increased using a higher amount of aggregate, rugosity can be altered using aggregate of different dimension. Crucially, as Seacrete is an elastic material that is flexible yet stiff, long-term stability on the sea floor is to be expected (currently several months).
In addition to oyster recovery, Seacrete is also being explored as a substrate for coral outplanting, sea grass relocation, and urchin restoration.
Below are a few photos of the ecological projects that we are currently exploring with Seacrete.
