What would happen to aquatic organisms if solid water were denser than
liquid water?

Let's say it's below the freezing temperature of water. Well what would happen is the water up here would freeze. And this is actually what does happen. Water at the surface would freeze, but if this ice were more dense, the solid water were more dense than the liquid water, well then the ice would sink.

Explanation:

answer; polycythemia is the correct answer;