The world ocean is in great danger of collapse. In a study of 154 different marine fish species, David Byler found out that many factors such as overfishing, climate change, and fast growth of fish populations will cause ecosystem collapse. When humans fish, they usually will fish the populations of the higher trophic levels such as salmon and tuna. The depletion of these trophic levels allow the lower trophic level to overpopulate, or populate very rapidly. For example, when the population of catfish is depleting due to overfishing, plankton will then overpopulate because their natural predator is being killed off. This causes an issue called eutrophication. Since the population all consumes oxygen the dissolved oxygen levels will plummet. The dissolved oxygen levels dropping will cause all the species in that area to have to leave, or they will suffocate. This along with climate change, and ocean acidification can cause the collapse of an ecosystem.