Robotic reef

Our team hard at work assembling instruments on the 

scaffolding tower.

Coral reefs are growing day in, day out, constantly constructing the calcium carbonate skeletons that form the reef. The reef does not have working hours. Unfortunately, we do.  We can only take small boats onto the reef during daylight hours. That gives us only half of the story of what’s happening on the reef. Photosynthesis dominates in daylight, respiration at night – like the reef inhales all day and exhales in the night. To understand how the reef is growing and “breathing”, we need to sample changes in the seawater chemistry at all times of the day.

Katie inspects the RAS - excited that the RAS is in the

water and starting to collect samples.

One solution is to program “robots” to sample around the clock. On Dongsha, we have instruments deployed on the reef that are continuously measuring the temperature, salinity, pH, and current speed of seawater flowing onto the reef. To measure net ecosystem calcification (NEC), which tells us how quickly the reef is growing, we need to collect bottle samples of seawater after it has flowed across the reef. The calcifying organisms of the reef, including corals and coralline algae, use ions in the seawater to build their shells and skeletons. Using seawater samples, we can measure how quickly these ions are removed from seawater, which gives us a measurement of the reef-scale calcification rate – and how this calcification rate changes as “internal” waves crash onto the reef.

The largest, and most complicated, “robot” that we have deployed on Dongsha collects seawater samples for us at all hours of the day, called the “Remote Access Sampler” or “RAS”. But the RAS is 5 feet tall and weighs over 300 pounds, and we need to deploy it from a small boat at shallow depth (~2 meters at high tide) on the reef 25 kilometers from Dongsha Island. In other reef systems, we assemble the RAS on land and bring it on a boat to where we want to sample. On Dongsha, instead we built a scaffolding tower out on the reef, brought the RAS in pieces to the reef, assembled the RAS on the tower, and lowered it into the water.

Assembling the scaffolding tower and the RAS took several days, but that was time well spent. The Dongsha reef is being sampled around the clock, while we are sleeping or eating dinner on the island. This gives us time to collect additional samples, such as cores of skeleton from individual coral colonies (more on this soon).

 The time-lapse videos below show us lifting and lowering the RAS in the scaffolding tower.

- Tom DeCarlo

Joint Program in Oceanography

Woods Hole Oceanographic Institution