I'm reading a webtoon called "Deep Sea Water"—if the sea levels rise and all land disappears, will humanity be pushed out by marine life?

In the story, people live miserably on ships, being pushed aside by creatures that have grown massive like mutants.
If most of civilization is destroyed during the process of rising water levels, would it be correct to assume humanity would be pushed out because it would be difficult to develop civilization and sustain the population with food without any land?