Definitely the phytoplankton since it provides the bulk of Earth’s oxygen production. Oxygen only exists because the ecosystem replenishes it. If all oxygen production stopped it would only take a few thousand years to deplete completely. Oxygen binds quickly with everything around it.
Phytoplankton
It’s true, but Phytoplankton is not an animal.
Definitely the phytoplankton since it provides the bulk of Earth’s oxygen production. Oxygen only exists because the ecosystem replenishes it. If all oxygen production stopped it would only take a few thousand years to deplete completely. Oxygen binds quickly with everything around it.
Real answer here