If left alone, Lionfish will infest everything, and there will be almost no fish left on the reef which causes the reef to fail. The reef needs fish that clean other fish so they can be healthy and also needs fish and other creatures that clean the actual coral and reef structures and sponges and such. We also need little fish for native species to be able to eat and grow and this is how the reef works! When you have one creature that has no predators eating up all of these fish and not leaving