Coral Reef Arks: An In Situ Mesocosm and Toolkit for Assembling Reef Communities

Coral arks can answer key questions about how marine communities assemble, change over time, and respond to changing environmental conditions, including how the biology changes the abiotic environment. Coral arks provide a replicable, scalable, and vertically adjustable research platform for building and experimenting with coral reef communities in their natural environment and at the ecosystem scale. This method of combining ARMS and arks to build ecosystem mesocosms can be applied to benthic marine communities living throughout the planet, especially those found in coastal areas.

After transporting the sand screws to the benthos, place the sand screw upright, and bury the sand screw by twisting it until the first disc has been covered in sand, or loose rubble. Place a five foot long metal turning bar through the eye of the anchor, so that most of the turning bar sticks out of one side of the eye. While walking, or swimming in circles on the benthos, screw the sand screw into the substrate until only the eye remains sticking out of the benthos.

Install three sand screws in a triangular pattern connected by a chain bridle for increased holding power. To assemble the geodesic frame, screw a stainless steel hex nut onto a 2.5-inch stainless steel bolt 3/4 of the way to the top of the bolt. Insert the bolt into one of the inside-facing holes on the strut, and secure it with a locknut to prevent the hub from sliding down the length of the strut.

Now, push the end of each strut through one of the hub's holes. Fasten another bolt through the strut's outer hole, and finish with a locknut to prevent the strut from sliding out of the hub. Repeat for all five struts in one hub.

Then add hubs and struts until the geodesic sphere is assembled. After unspooling the 1/8-inch stainless steel wire rope, begin threading it through the struts. Create 12 loops out of nylon cable ties about the size of a silver dollar, one for each hub.

As the wire rope is threaded through the struts, pass the rope through the zip tie loop at the hub, and then continue to the next strut. Continue threading the wire rope through all the struts connected in the middle of each vertex by the zip tie loop. After threading the cable back to the starting point, pull the zip tie loops using pliers to bring the lengths of wire rope close together.

Fit a 1/2-inch stainless steel cable clamp onto all the wire rope lengths and tighten down securely. Repeat for all the vertices of the structure. Now, mate and clamp both the ends of the metal wire using three 1/2-inch cable clamps.

Add the rigging system composed of two lengths of three by eight inch stainless steel cable that is hydraulically swaged onto an eye at each end. Pass the bottom ends of the cable through the top and bottom of the ark, fitting the end caps onto the top and bottom hubs using a mallet. A turnbuckle system in the middle connects the two lengths of stainless cable.

Screw the eyebolts into the turnbuckle, and tighten them until there is sufficient tension on the structure to make the system rigid. Add each molded fiberglass grating cut into two half pentagons into the ark interior using heavy duty 250 pound strength zip ties to anchor the sides of the platform to the ark struts. Place one length of fiberglass I-beam to join both halves of the fiberglass platform underneath the structure, and secure to the underside of the platform using two stainless steel U-bolts, and secure with nylon insert locknuts.

Repeat for the other four I-beams, equally distributing them down the length of the platform. This joins and supports the two halves of the platform, creating a full pentagon. Tighten the heavy duty zip ties at the edges of the platform and clip off the excess.

At the end of this step, the internal platform is firmly integrated into the ark structure. Use stainless steel mousing wire to mouse the ends of the turnbuckle and all the shackles. At the end of this step, the ark will have two integrated platforms, top and bottom attachments for hardware attachment, and a central cable that bears the bulk of the tension force placed on the structure via anchoring and positive buoyancy.

Once the frame is completely assembled, install the geodesic frame at the deployment site. To measure the in-water weight of the arks, attach the submersible load cell to a block and tackle pulley system to temporarily transfer tension on the mooring line to the strain gauge system. Attach the base of the block and tackle to a secure location on the ark mooring system, such as an intermediate shackle point, or to a sea floor anchor.

Attach the top of the load cell to a secure location on the ark mounting framework. Without removing, or altering the mooring components on the ark, pull the line through the block and tackle and pulley system such that the tension is transferred from the ark mooring system to the pulley system, cleating the line with each pull. Ensure the mooring line is completely slacked to allow the strain gauge to collect tension measurements.

After at least several minutes of data collection, slowly transfer the tension from the block and tackle pulley system back to the ark mooring line. Ensure the shackles and other mooring components are properly seated and secure. The response of two shell ark structures shows a drag force of less than 10 kilograms and net buoyancies of 82.7 and 83.0 kilograms.

The current speeds during the measurement period were relatively stable at about 20 centimeters per second. The ark's environment exhibited higher average daytime light intensities, higher average flow speeds, lower dissolved organic carbon concentrations, and lower diel fluctuations in dissolved oxygen concentrations than the benthic control sites located at the same depth. Differences in temperature between the arks and the control sites were insignificant.

The arks also displayed microbial communities with higher virus to microbe ratios than the control sites, driven by a lower abundance of microbes and a higher abundance of free viruses in the mid-water ark's environment. The microbial communities on the arks were composed of on average physically smaller cells than the microbial communities at the sea floor sites. The survival of experimentally translocated corals was assessed every three months at the arks and control sites.

Nine months after the translocation of the first cohort of corals, more corals were still alive in the arks compared to the control sites. Coral ark systems are designed for long-term ecological monitoring projects, so anchoring systems and structural designs should be selected considering both normal and extreme conditions at deployment sites. Abiotic factors associated with coral arks communities can be adjusted by changing the depth of the systems, enabling investigations into how reef viral and microbial communities respond to changing environmental conditions.