He doesn’t need an ark full of animals to achieve that.
He doesn't need very much of anything, yet He chooses to do things such as salvation through boats. As I mentioned previously, Dr. Brown's book discusses the catastrophy of a cooling planet and how water was the lubricant that allowed the continents to break up and reform. Earthquakes would have been pegged at 10.0 on the Richter and I doubt very much of anything would have survived. A boat floating on a newly formed sea gave them the insulation from such an event.
Right, and He didn't NEED a rib from Adam to make Eve either, but He did it that way because it communicated many truths to us. In the case of Adam's rib, God showed us a beautiful picture of how a husband and wife would be bone of each other's bones, how Eve came from close to Adam's heart, his companion, and the bone marrow from Adam's rib blended his blood with hers, his life giving force with hers, all of this showing us just how beautiful and important husbands and wives would be to each other in God's plan.
So it was, when God found it necessary to wipe the evil from the earth and start over, he did it in such a way that would paint a picture (communicate the idea) for us of God's promise to save those who chose with free will to belong to God. The ark, was a picture of Jesus. Jesus is our ark. If we believe, if we accept the gift and "get aboard" so-to-speak, Jesus will save us from the inevitability of God's righteous judgement of our sin.