"Seventy percent of the world's oxygen comes from phytoplankton. Sharks, as an apex predator, feed on many of these plankton-eating fish. Slapped with a stigma as people-killers from the popular "Jaws" series, sharks actually save lives — they help provide the world's oxygen supply."Let's put this one to rest -- forever. The answer is no. There are no scientific studies that link shark populations to the global supply of oxygen. If we are mistaken, and there is a study, please forward it.
Now we are just as guilty as others in promulgating this shark-oxygen relation (here and here), and for that we apologize. Mea culpa.
In our list of 10 Things You Can Do To Protect Sharks we list #1 as Educate yourself about the global situation of sharks. On this oxygen issue, we recommend starting your education with Rick Macpherson's recent blog at Deep Sea News and Patric Douglas' blog at Sharkdiver.com.
This is not, however, a repudiation of the fact that sharks maintain overall ocean health. There are many, many studies that link sharks to coral reefs. Also, the removal of large sharks can negatively impact whole ecosystems by, for example, allowing an increase in the abundance of their prey (fewer sharks eat less prey), or influencing prey species through non-lethal means, by causing behavioral changes to prey habitat use, activity level and diet. A science report by the Pew Environment Group titled Sharks:State of the Science is an excellent resource for referencing many of these studies.