The ecosystem doesn’t work in a top-down, totalitarian way. The system is not always in flawless harmony. It inexorably stays with the troubles.
The Bioluminescent Predator Squids have emerged very recently. The invertebrates live in the deep sea where sunlight can not reach so that their translucent bodies are barely visible. They artfully use bioluminescence to attract prey. When the invertebrate illuminates the fishes that are not digested yet, it appears through its translucent body like a group of glowing fishes. The uncontrollable increase of their population threatens the marine biodiversity of the island by depleting the population of deep-sea animals.
Human dwellers in the islands figured out that the squids could glow due to the symbiosis with their intestinal bacteria. Humans later mimicked the relationship between the squids and the bacteria for lighting up their houses.