It consumes carbon dioxide. It does not consume 20% of the world's oxygen.
Sadly the ocean is becoming so polluted that it's very worrying that 80% of our oxygen comes from the sea especially with Fukushima still leaking its radioactivity into the beautiful ocean.
People need to stop being so greedy and start appreciate this beautiful planet.
Thinking that plants only consume CO2 is wrong. They also comsume O2. As a tree gets older is consumes less and less CO2, until at some point - this varies depending on species - they start to consume more O2 than they produce. A Very mature woodland does not produce much in terms of net O2.