Roughly a half of the oxygen on earth is produced by phytoplankton in the ocean while the other half is by plants on land.
A Nature article reveals that phytoplankton are decreasing substantially probably due to the higher ocean temperature caused by the global warming. In addition to the major source for the earth oxygen, phytoplankton are the basis of the food chain in oceans. With such essential roles for the earth environment, this significant decrease of phytoplankton will likely have a serious impacts on the future earth environment.
Dr. Falkowski, who commented on the article, expressed a concern that "We're squeezing big open-ocean fish like tuna and swordfish from both ends." That is to say we are not only overfishing big fish from above (land) but also threatening their existence by destroying the marine food chain from the bottom (ocean).
Nothing human being have been done for good?
By the way, Boris Worm, one of the article authors, is a Census of Marine Life researcher and I have met him before.
Related news article from Scientific American