There are dead zones off many of the coasts of the most populated coastal cities around the world and the crisis is becoming too serious to ignore or deny.
Yes, human civilizations need to continue, but they also need to do it in such a way that it makes sense and does not harm our oceans, as the sea brings us life, food, and enjoyment.
Today there are dead zones off the coasts of Shanghai, Beijing and other major human cities in excess of 250 square miles.
The fish if you can find any are full of toxins and poisons and the oxygen in the water is highly depleted.
Something must be done.
  One interesting concept is to use underwater propellers to create cavitation, thus, oxygenating the water that is depleted.
A series of propellers with guards to prevent fish killing would be set up in the worst areas where the mitigation is needed.
The system would rest on the sea floor and be movable as the sea life sprang back to life.
The systems would need to be made out of space age materials to handle the salt water and the power would need to be capable of harvesting ocean wave energy to power up.
These systems must be mass produced and sent all over the world to solve this growing crisis.
Mankind needs the sea to survive and when the oceans thrive with life so can mankind.
Humans are very much part of the eco-system and also the food chain, failure to adhere to this logic will spell the demise of millions of people in the future.