In the end that's exactly what Nereis wants. She wants humans to see past the romantic image that we have created in our head of the mysterious depths and vast expanses of ocean life and remember that the seas are filled with living creatures. Our lives are irrevocably linked to her health; if the oceans die our chances of survival are next to nothing, and she will surely die if we continue to only see her in terms of something rich and strange instead of a living breathing organism.
Patricia McKillip has created the perfect red herring with Something Rich And Strange. Her characters and scenarios make for an updated and entirely plausible story of the Siren's song, as it touches upon the oceanic outcome for those who would hear and heed. The author plays upon our willingness to believe in the cruelty of the deep sea and Sirens until at the last second she stands it upon its head and shows us that we are as blind as Jonah when it comes to what lies beneath the waves.
Patricia McKillip has a command of the English language that is as beautiful as any writer I have read. She can summon sights and sounds to magically appear in the mind's eye, like few others. If I ever were able to go to the deep places of the ocean I have no doubt — having read Something Rich And Strange — that I will already have a good idea what they will look like.
This is not a "message book" in the sense that you are beaten over the head with anything. It's a wonderful story that just happens to remind us of our obligations to those we share our world with. Fantasy and myth are wonderful, but sometimes reality is even more spectacular.