If there was a fungicide that killed all fungi, make a prediction on how that would affect the ecosystem and eventually us humans

Fungi is one of the main source of food in ocean. That would mean all of algea eater planktons will die. If planktons die new small sea creatures wont be able to eat anything and die. Death of fishes will kill all of fish eating animals. Their death will kill their hunters and so on. As well as we get various sources from algea , and they produce oxygen. It would be really bad . But problems would show off by time