SOLVED. YA Fantasy Book involving mermaids and mysterious creatures. Spoilers ahead. [s]

[MG]

GENRE: YA, fantasy, mermaids, mythical creatures.

I believe this was a first book in a YA series.

BOOK READ: Between 2010-2013. This was a smallish book on my lit. teacher's bookshelf that she allowed me to borrow. 9-11 years later, I am still thinking about it and would love to find it and read it again.

PLOT DETAILS: This book features mermaids/merfolk as the main characters, set underwater. The main character was a YA-age mermaid. I remember some of the merfolk had one tail and others had two tails or leg-like appendages. The merfolk raised these creatures that I believe would grow up to very powerful and/or rulers in some way. These creatures were not humanoid. The main character somehow helped in the nursery for these creatures. These creatures can become bonded with the merfolk and I believe this bond was usually reserved for those in positions of power.

SPOILER AHEAD

(view spoiler)[ The climax of the book ends up being that the enemy character poisons the water of a room of the good guys all gathered in one area for some planned event that our main character is not at. The survivors of the coup are those who helped orchestrate it and had special masks to prevent themselves from being poisoned. The main character loses someone or multiple people important to them. The final scene of the book is the main character waking up (on a beach?) with a mark on her (hand?) meaning she has been bonded to one of the important/powerful creatures. It ends with a new call to action of her finding said creature and avenging/saving what was lost. (hide spoiler)]

[Becca]

This sounds like the Water series by Kara Dalkey - the first book is Ascension.

[MG]

Becca wrote: "This sounds like the Water series by Kara Dalkey - the first book is Ascension."

That's it! Oh my gosh, thank you so much, I have been looking for this for so long!