We know that there has been a big shift already ?we are replacing big tuna and billfish with things like snake mackerel and pelagic stingrays. This is a fundamental change in the world's oceans."
To understand what creates these patterns of diversity, the scientists collaborated with oceanographers to examine different open ocean "habitat" features. Sea surface temperature and the level of oxygen in the water were the most important factors in determining where the big fish in the open ocean congregate. These hotspots were mostly in subtropical areas with warm waters, sufficient oxygen, and sharp temperature gradients that serve to aggregate food supply such as zooplankton and small fish.
"The peak in big fish diversity is at middle temperatures," says Myers. "Like Goldilocks and the three bears- ocean animals don't like it too hot, or too cold, they like it just right." For these predatory fish, 22 degrees C (77 degrees F) seems to be the optimum temperature.
The only other global study of oceanic diversity is for foraminifera -- tiny, single celled zooplankton. These two studies show surprising congruence. "The smallest animals in the ocean and some of the largest show the same pattern of diversity at the global scale," says Steven D'Hondt an author of the 1999 Nature paper on zooplankton. "I would have never woken up and said that tuna necessarily show the same diversity pattern as plankton. This study is just really neat. It tells us something about the connection of diversity and ocean structure and it shows that human activity is changing those patterns for the largest fish."
Hotspots for Conservation?
These open ocean hotspots appear vitally important for many different species, from zooplankton to tuna, and ?despite shrinking ?have stayed relatively constant in location over the past 50 years. This new information is timely for policy-makers as the United Nations General Assembly