The reef

Martin leaned back and looked over his shoulder at me. “So? Where to now?” he asked.

“Keep going northeast, along the ridge,” I answered. In front of me, the sonar glowed with a ragged stripe down the middle of its semicircular scope. I was in the ROV control van – a shipping container filled with monitors, servers, and controllers galore – on the deck of R/V Polarstern. The ROV was 1800 m below us, on top of a narrow, rocky ridge with sheer cliffs on either side. The seafloor was rough, with stones from the size of a grape to the size of a loaf of bread scattered across or buried in the mud. Sponges were everywhere – round ones and branched ones and tall ones and puffy ones. Hundreds of them, plus a number of species we had not seen at the last station. I had written a paper about this reef, located in the center of the HAUSGARTEN observatory, back in 2012, and I was overjoyed to learn more about it.

One of my larval traps deployed on the seafloor. The lids will
open automatically after a day. Photo by the ROV Phoca team.

Martin pushed a few buttons on the dashboard in front of him, and the ROV slowly lifted off the seafloor. We flew along for a few minutes before I pulled out the green laser pointer the pilots had given me. In a dark, crowded van, it was the most efficient way for me to point at the screen.

“How about there?” I circled a small rock with the green light. Martin looked up at the monitor where I was pointing, made some adjustments to the ROV’s thrusters, and settled gently on the rocks, right in front of the one I had pointed out.

One of my cages deployed on the seafloor over a stone.
I'll come back in 2 years to see if keeping predators away
has had any effect on the sponge community. Photo by the
ROV Phoca team.

Over the course of 6 hours, the ROV flew around the top of the reef, stopping every few meters to deploy my experimental gear. I had prepared larval traps similar to the ones that were deployed on moorings, in order to see what larvae disperse close to the seafloor. I had made cages out of PVC and plastic netting to exclude predators and observe what effect they have on the sponge community. I had made simple frames to surround stones and serve as control plots. One by one, my creations were deployed on the seafloor, and with each one, my excitement mounted. I cannot wait to see what my experiments show.

Now the waiting begins – it will be two years before I can return to the dive sites and observe the results of my experiments. I am extremely grateful to the ROV team for their help and to my AWI colleagues for enabling my participation in the cruise. Hopefully I will get good results!