The Collapsing Arks group, made up of Mechanical Engineering students Brandon Khamenian, Chad Zuanich, Nathan Hutchinson, and Gary Baldevarona, considered one of the most persistent and frustrating challenges faced in coral restoration efforts: destruction from storms. Hurricanes destroy large swaths of reef by breaking down the three-dimensional reef structure that corals build; hundreds of years of coral growth will be destroyed in only hours. Under ideal conditions, and given enough time in between major storms, corals will recover fully and even thrive in the aftermath of hurricanes, as the breakage spreads corals to new locations across the reef.
However, climate changed has caused an increase in the frequency and intensity of hurricanes and tropical storms, and this, combined with changing reef conditions, has made it hard for corals to rebuild the three-dimensional framework essential to the success of coral reef ecosystems. Reefs worldwide are “flattening” as a result. Purpose-built and placed structures, such as infrastructure for coral restoration (coral nurseries, artificial reefs, etc.) also suffer from these types of storms, which will wipe away years of progress and investment in astonishingly short periods of time. The Collapsing Arks group decided to build a structure that would be more likely to survive major storm events, and might even be able to use storms to their advantage.
The prototype for the Collapsing Ark is made entirely from stainless steel, with custom-made joints and connection points. The structure is designed to sit on the seafloor (installed securely using pilings or other anchor points), instead of up in the water column, and thus directly increase the structural complexity of the reef it is anchored on. Fully assembled, the Ark stands almost 9 feet tall. A force plate in the interior rests against a small acrylic shear pin, which breaks when a certain force is applied. As the current speed flowing across the Ark increases to a critical threshold (for example, during a storm event), the force plate breaks the shear pin and the structure collapses, with the top pyramid inverting into the structure. This collapse lowers the vertical profile of the Ark by about one third, reducing the drag force that storm-induced currents have on the structure and in doing so, reducing the likelihood of damage. This collapsed configuration serves the dual benefit of breaking off corals growing on the structure, which over time, could infill the Ark and create large, boulder-like structures that could replace structural complexity and protect coastlines from wave action.
Testing in Mission Bay using our strain gauge system confirmed that the Ark collapses consistently when 80 lbs of force is applied; the equivalent of ocean currents moving at approximately 2 m/s. For perspective, if you have ever felt pulled by a swift current in the ocean, you were likely not experiencing more than 0.5 m/s. The Collapsing Ark group's Ark design fits nicely into projects that seek to build self-sustaining reef ecosystems that replace ecosystem services like coastal protection and recovery from storm damage.
The Electrified Arks group, made up of engineering students Courtney Brumm, David Trinh, Max Herrbach, and Gannon Gorman, identified the slow pace of reef growth and establishment as the challenge around which they would design their structure. Corals lay down a hard, calcified skeleton as they grow, which is an energetically expensive process and thus happens slowly. This slow pace of coral calcification gives the upper hand to rapidly-growing, non-calcifying algae, which compete with corals for space on the seafloor. Restoration efforts around the globe must work tirelessly to manually remove algae and other fouling organisms from their submerged structures in order to provide corals with the space to grow and propagate. Efforts that will reduce this algal overgrowth without the need for divers to do it manually are needed to bring coral restoration projects to scale.
The Electrified Arks group decided to build a structure that uses active electrolysis to kickstart reef growth and provide an improved environment for coral calcification to occur. Active electrolysis happens when an electric current is passed through two dissimilar metals in seawater, which is an electrolyte (meaning electric current will pass through it). Electrons are passed from the power source through the first metal, called the anode, through seawater to the second metal, called the cathode. The passage of electrons between these two dissimilar metals in seawater causes calcium carbonate - roughly the same stuff as corals produce for their skeleton - to spontaneously deposit on the surface of the cathode. The ingredients for calcium carbonate are in seawater everywhere - changing the chemistry of the seawater using electrolysis allows it to come out of its dissolved form and into a solid. This process also increases the alkalinity of the water surrounding the cathode, which may increase the speed at which corals grow.
To build an Ark capable of active electrolysis, the Electrified Arks group built two metal frames in the middle of their Ark structure: one made from naval brass, and one made from rebar. The group then tested two methods for generating the electricity needed to pass an electric current through the metals. The first was a solar panel system mounted on a floating buoy frame on the surface. Electrical cables connected the solar panel directly to the metal frames, and evidence for the electric current generated between the frames will be seen in the bubbles forming on the metals (these bubbles form because electricity passed through seawater splits water - H2O molecules - into H2 and O2 gas). As a second method for electricity generation, the group built a custom turbine system mounted to the Ark outer frame, designed to capture energy as water flow passes over the structure. Both systems were able to generate enough of an electric current to fuel active electrolysis, and after several days, calcium carbonate began to deposit on the metal frame.
Active electrolysis is being applied successfully in several coral restoration projects around the world but has not yet been refined or studied sufficiently to be brought to scale. This technique may be a promising method to kickstart reef restoration, and to try and engineer the ideal chemical environment for corals to grow quickly and thus outcompete fleshy algae. Projects like this, which integrate methods of harvesting energy with methods of using it, and aim to alter the environment in ways that promote coral growth - are critical to scaling up coral conservation and restoration efforts worldwide.