This is really beautiful, and the colors are nice too~
That said, this painting also absolutely terrifies me (I'm deathly afraid of the sea) so you've accomplished many things here~
oh! I watched a documentary about Amazonian manatees once and this was actually included! they said apparently people would mistake them for mermaids because manatees don't really show themselves out of the water, they just poke their heads out slightly to get food off the surface and to breathe and stuff. And the food they tend to eat (leafy things floating on the surface and stuff like that) sometimes would get stuck on the tops of their heads as they poke em out of the water, giving the illusion that they have hair. This caused sailors and such, mainly at a distance of course, to mistake them for woman who lived underwater.
the little doggy freaking out and the boat tilting (from the weight of the creature im assuming XD) are a nice touch too.