Peter Ward, UW Biology Professor, authored an article recently featured in Nautilus. Peter has been studying the nautilus in the Mesophotic Zone for 45 years, and in this span of time, he has also seen the unfortunate and devastating effects that climate change has had on the conditions that have sustained life for millions of years.
"We were all very tired. My crew and I had been tracking nautiluses off tiny Ndrova Island in Papua New Guinea for close to a week. Every day we spent 16 hours on small dugout canoes and then got eight hours of fitful sleep on the deck of a Melanesian sea craft. Rice and fresh tuna for breakfast, lunch, or dinner. In the open boats, the sun, the wind, the rain, the dark, all seemed to merge. Time melted in fatigue.
A week before, we had fitted the nautiluses with acoustic transmitters that gave their position and depth. To track them, we had to stay within a kilometer as they bumped through a muddy habitat near the ocean bottom and climbed up the coral reefs lining the small islands here. We sat above them in small boats and canoes, dangling hydrophones over the side to pick up the faint acoustic signals.
It was 2015 and we were tracking the two different kinds of nautiliuses—Nautilus and its descendent, Allonautilus—found here and virtually nowhere else on Earth. Both varieties were going extinct from overfishing and changing ocean conditions. We wanted to know how they were managing to survive. Could they cross large bodies of water to find sufficient food?
In 1984, I had done this same kind of work, in exactly this place, but with inferior equipment. Now, 31 years later, my memory jangled. Major changes had occurred. Back then the water was blessedly cool as it rose up reef walls from deep ocean zones. To dive was to escape the heat of this place, a geographic hot spot athwart the equator. Now the rising water, deficient in oxygen and nutrients, was a warm death to the reefs it once sustained.
I was most struck by the absence of sharks. In 1984, we were repeatedly chased from the water. On one occasion, my dive buddy slammed his large camera against the head of an especially aggressive black tip as we scrambled over the transom and into our boat. Not so in 2015. We dived every day for two weeks. We never saw a single shark. Not even a tiny, white-tipped reef shark. I knew where they were. Or at least where their fins were. Hanging in the Thailand, Cambodia, Hong Kong, and mainland Chinese stores by the tens of thousands, waiting to become soup.
Our transmitters, miracles of miniature electronics that looked like AA batteries (albeit $1,000 each; pretty pricey for AA’s!), picked up the nautiluses as they swam above the bottom of the ocean. Each second, they sent us their position, their depth, and the temperature of the water they were in. They didn’t descend below 800 meters because at that depth the ocean pressure would cause their shells to implode. Our tracking showed they followed the ocean bottom contour toward shallower water, where there was more food, but also more danger. Their predators, sharks and large fish, are visual hunters, so the nautiluses were safer in the darker, deeper depths. At least they once were.
In 2015, our research brought me a revelation that my colleagues in marine biology and paleontology and I are still sorting out today. Although the nautilus doesn’t face as many predators, whose own hunter, humans, have reduced their numbers, the buoyant, deep-sea organism with the beautiful spiral shell faces a bigger problem. The water temperature in the ocean layer, defined as the Mesophotic Zone, through which the nautilus travels, is growing so warm that it’s destroying the life of all the organisms that thrive there."
Read the full article in Nautilus.