They have a lot of enemies, so these can be thought of as traits evolved for survival.
The blue hair blends with the color of the water's surface to avoid predators from above.They don't always stay on water. They make their nest in island or other safe places and eat fishes or water grasses.Aquatic Marisa's were originally an improved species made for being pets. This is the species of Aquatic Marisa that has adapted to wild life. Their hat is bigger and more water resistant.
But the most surprising things are, their hat is white and their hair is blue.Likewise the white hat makes them more difficult to find by the enemies from below