SCIENCE

By the Numbers: A Marine Advisory

Scientists say the outlook for the world’s oceans is bleak—unless we stop overfishing and reduce air and water pollution

Sarah Zielinski

August 2010

Nancy Knowlton marine biologist — Nancy Knowlton is a marine biologist at the Smithsonian's National Museum of Natural History and a leading authority on coral reefs. Christian Ziegler

16.1 billion pounds: total amount of fish that commercial fleets kill or fatally injure before discarding at sea each year

3 pounds: amount of wild mackerel or anchovies needed to produce one pound of farmed shrimp or salmon

82.4 percent: decline in the spawning population of western bluefin tuna since 1970

33 percent: amount of U.S. crude oil production from offshore sources

0.7 parts per billion: concentration of weathered crude oil in seawater that kills or damages Pacific herring eggs

100 percent: projected increase, by 2100, in the number of coastal dead zones, where bacteria spurred by pollution deplete oxygen from the water and make it impossible for marine animals to survive

0.7 percent: proportion of the world’s oceans that are part of marine protected areas

15 million years ago: the last time CO2 levels in the atmosphere were as high as they are today

2037 projected year when the Arctic will become almost entirely free of summer sea ice due to melting

2050 projected year when coral reefs worldwide will shrink because of increased ocean acidity as atmospheric carbon dioxide, from burning fossil fuels, dissolves in seawater

Nancy Knowlton, a marine biologist at the Smithsonian’s National Museum of Natural History and a leading authority on coral reefs, says a significant increase in ocean acidity puts virtually all marine animal species at risk. That’s because acid can kill larval fish and shellfish and keep corals and animals at the base of the marine food web from building skeletons. “In the long term,” Knowlton says, “if we don’t deal with carbon dioxide emissions, we’re in real trouble.”