SBU Study: Think There's Plenty of Fish in the Sea? Think Again

In a study published this week in the online journal Proceedings of the Royal Society B, a pair of researchers at Stony Brook has found that there aren't as many fish in the sea as people seem to think.

Dr. John J. Wiens, an associate professor in the Department of Ecology and Evolution, and student Greta Carrete Vega explored the reasons why the ocean is home to only 15 to 20 percent of the world's species despite covering 70 percent of the Earth's surface.

Their research pointed to striking differences between the biodiversity of freshwater habitats and that of salt water habitats.

“There are more fish species in freshwater than in saltwater habitats, despite the much greater area and volume of the oceans,” Wiens said, adding that freshwater environments occupy only about 2 percent of the Earth’s surface. “More remarkably, our results suggest that most marine fish alive today are descended from freshwater ancestors (even though fish and animals in general first evolved in the oceans).”

The researchers studied the biodiversity of ray-finned fish, which covers 96 percent of all fish species. Based on the evolutionary tree analysis of molecular data and fossils, they hypothesized that hundreds of millions of years ago, extinctions in marine habitats has led to the present-day lack of diversity in marine fish.

“Our results suggest that ancient extinctions in the marine environment may have wiped out the earliest ray-finned fishes living in the oceans, that the oceans were then recolonized from freshwater habitats, and that most marine fish species living today are descended from that recolonization (leaving less time for biodiversity to build up in the oceans),” Wiens said. “This pattern of ancient extinction and more recent recolonization may help explain why the oceans are now so species-poor, even for fish.”