By 2050 oceangoing plant and animal life will disappear on a scale equal to the five great global extinctions of the past 600 million years

the International Programme on the State of the Ocean : researchers
The deadly triad of pollution, overfishing, and climate change are impacting the world’s oceans to greater extents than even the IPCC’s worst-case scenarios had predicted.
It would be a tragedy to lose so many species of fish, coral, aquatic mammals, and other cherished wildlife, not only for their sakes, but for humans who depend upon the oceans for their livelihoods, as well — as the report’s authors explicitly state, fishing and maritime industries, large and small, across the globe, could be driven out of business. BUT… The world community can avert this massive loss of life, the report states, through concerted international action to mitigate greenhouse-gas emissions, rescue endangered oceanic ecosystems, and protect the oceans’ health on a global scale.

"International Earth system expert workshop on ocean stresses and impacts", 2011