If the underwater forest is a natural experiment, the gas rig offers an experimental control. Beneath the sea surface, the towering bases of the rig serve much like the eroding underwater stumps or any object tossed into these vacant waters: They are all “fish collectors,” Dr. Helmuth said, providing structure for sea life and people to enjoy.
The team wanted to see if deploying wooden blocks along the base in the future might address questions that can’t be asked at the underwater forest: Did the forest attract marine life that was already in the surrounding areas, similar to what is drawn to a gas rig? Or did it give rise to a unique ecosystem? How long does wood typically last underwater among wood-eaters under different environmental conditions?
The vessel, having reached the rig, idles on foamy water beneath its rigid steel beams, in a sticky, highway-scented mist. Three divers jumped in, disappeared and returned a few minutes later with good news: Visibility was perfect, and they captured great footage of the sea life to compare with footage from a previous dive in the forest.
Fog swallowed the rig as the boat left it behind. Then it swallowed the boat. Temperature dropped. The divers changed into dry clothes. Everyone rested.
The ship passed a lighthouse where shallow water washed over a beach. Buoys appeared, marking the ship channel in and out of Mobile. Farther off, shrimp boats floated between gas rigs.
If the rigs are a reminder of human activity, the forest is a reminder of what climate change can do, Dr. Helmuth said later. Since the Industrial Revolution, the change in environmental conditions produced by humans is comparable to what it took for natural processes to grow, kill and bury the forest over the course of 100,000 years.
The rolling weather signaled that time had run out for further examination of the forest. Luckily, during a sea-sickening dive on the prior Saturday, they still managed to collect six large buckets of logs, branches and roots.