Dark Tides series by Devyn Quinn (Books 1-3)

Devyn Quinn lives in the scenic Southwest, though she has called several other states home. She is a huge fan of dark gothic literature, and read tons of books on history and biographies. She especially enjoys reading books on Hollywood before the 1960's. Now divorced (happily so), Devyn lives with her cats, four ferrets (yes, four!), and Shih Tzu, Tess.
Genre: Paranormal Romance

1. Siren's Call
Lighthouse keeper Tessa Lonike savors her solitude on Little Mer, an island off the coast of Maine, guarding her true identity as a mermaid. But when Tessa spots a man thrashing around in the ice cold waters during a storm, she must use her ability as a mermaid to pull him to shore. And a year later, when Kenneth meets her again, he's determined not to let Tessa slip away. But when Tessa'a archaeologist ex-lover comes back to town with a clue to her heritage, she may be forced to leave her happiness behind...

2. Siren's Surrender
Never embracing her mermaid heritage, Gwen Lonike lives in the human world as the owner of a Maine B&B. But when the gateway to a lost mermaid kingdom is opened, freeing its dangerous queen, Gwen can no longer hide, nor keep her secret from covert agent Blake Whittaker, who's assigned to trail a strange thread of paranormal activity.
How long can Gwen and her sisters remain safe from a destructive queen, and from Blake's superiors, whose ultimate mission could prove the greatest threat of all?

3. Siren's Desire
After defeating the covert agency that threatened to destroy her and her sisters, Addison Lonike grudgingly resumes her life as an EMT in Maine. She would love nothing more than to take on the dangerous Mer queen, Magaera, who is hell-bent on destroying them. But with two baby nieces on the way, she can’t take the risk. That is, until Mason McKenzie arrives…
Captain of the naval task force on the hunt for Queen Magaera in the Mediterranean, Mason sees the perfect recruit in Addison. But while at sea, the pair is pulled under a wave of passion that threatens their independent natures—and their mission. An encounter with a new race of male sea-shifters further complicates Addison’s desires. Now, she must choose between a life of the sea, or fulfilling the deepest longings of her heart…