I agree that taking one specific animal out of a complex system that had a long time to adjust will produce big changes. Killing the wolves allowed the deer to thrive. We wanted lots of deer, so that was good for some time. Now we don't hunt enough of them, so we need wolves again.

I agree that the oceans change - a lot - due to human influence. Some species will dwindle in numbers and disappear. It takes a long time for new species to emerge. But what I'm not so sure is that the overall change necessarily would have to be so negative in the long run.