What will happen to aquatic life if the water they live in becomes too warm?

Well, like polar bears and seals they need the water cold because they need the ice to be on. The ice is like a landing so they can watch from above and dive in and get their prey. If the ice melts then it will be hard to do that and some polar bears can drown if there isn't enough ice. Plus they are like humans in a way. We live at a certain temperature and our body is used to it. It would be like taking a human from Alaska and putting them into Arizona in the summer. The temperature is very different and it would be hard for that person to get used to it, if they lived where it's normally cool/cold. The fish and plant life are used to cold water so having warm water could kill them. Not all creatures can get used to new changes.