Which sea creature can change from male to female during its life?

A clownfish can change from male to female during its life.

Clownfish are sequential hermaphrodites: they begin life as males, and the largest individual in a social group can become female. The next-largest fish generally becomes the breeding male. If the female disappears, the breeding male changes sex and a subordinate male takes his place.

This arrangement fits the lives of clownfish in sea-anemone groups. A single anemone may shelter a small social hierarchy rather than a large, constantly changing population. Keeping a breeding female and male in place allows the group to reproduce while preserving its limited territory.

The fish live among the tentacles of host sea anemones and gain protection from predators. Clownfish have a mucus coating that helps them tolerate the anemone’s stinging cells. In return, their movements and waste can benefit the host, making the relationship a notable marine example of mutualism.