Biologist: Dead zones in the ocean threaten our most important food fish – Oxygen minimum zone ‘to start in North Africa and go all the way down to the tip of South Africa’

By Lynne Rossetto Kasper
9 May 2015 (Splendid Table) – Three years ago, I interviewed Eric Prince, a research fisheries biologist at the National Oceanic and Atmospheric Administration’s Southeast Fisheries Science Center. He and his colleagues had found that a huge dead zone, an area of the ocean with very little oxygen, had developed in the Atlantic. It spread from the east coast of South America across the ocean to the west coast of Africa; it was the size of North America. “Ninety-five percent of all the marine organisms in the ocean depend on adequate levels of dissolved oxygen,” he said. “They tend to be squeezed by this hypoxia [diminished oxygen] into a very narrow layer at the surface of the ocean. In the process of being compressed near the surface, they become a lot more vulnerable to overexploitation by surface-eaters. This involves some of our most important food fish, yellowfin tuna for example.” He explains what has happened in our oceans in the 3 years since we spoke. Lynne Rossetto Kasper: Could you explain what you found when we talked to you in 2011?

Eric Prince: The paper that I discussed with you last time was published in Fisheries Oceanography in 2010. That paper focused on the Atlantic Ocean, which is much smaller than the Pacific Ocean, which had already-documented oxygen minimum zone results in hypoxia-based habitat compression.

LRK: Meaning zones in the ocean where there was no oxygen in the water?

EP: Right, or very little. The animals in the surface mixed layer above the thermocline — there’s a tremendously productive population of animals in that zone, but not much below. That was really the essence of it: Everything we found in our previous paper in the eastern tropical Pacific, we also found very much applied to the eastern tropical Atlantic as well. Only it was a smaller body of water, the hypoxia and the oxygen minimum zone wasn’t as large. It wasn’t quite as hypoxic, meaning it had a little bit of oxygen, but not enough to support the tropical pelagic predators that we work with. […]

LRK: So with climate change …

EP: It’s getting warmer, and the surface water temperatures have been predicted by climate models to increase as much as even 5 degrees Celsius by the end of this century. I was in a meeting in London called Planet Under Pressure, and a very well-known scientist who’s really a leader in the world on hypoxia, Robert Diaz, gave a talk. I asked the question afterward: “All the projections of the temperature increase by 5 degrees Celsius — but if it even increases by half that amount, what would you predict in terms of the growth of the oxygen minimum zone? What about our pelagic fisheries?” I was really shaken by his response. He said, “The oxygen minimum zone in the Atlantic is going to start in North Africa and go all the way down to the tip of South Africa. It’s going to cover every single part of the eastern South American coast. We’re simply not going to have those fisheries.” [more]