I would like to ask of someone has also seen this sci-fi/horror movie about an island of "merfolks" Halfhuman and Halfseacreature. I don't think that this is an american film but the title goes like.. "The temple of the lost island" or " The island of the lost temple".
The story is I think about a couple having a cruise on a yacht then all of a sudden perhaps by storm or by any reason they reached and were trapped into this island. It is said that the island was cursed by a cult leader in the island.. turning the residents of that island into that kind of creatures. Then the couple discovered the hidden mystery of that island and the story is also related to a Gold thing... im just not sure about this. But in the end of the story.. the couple managed to get out of that island alive. The idea of the story is really AWESOME for me. Hope you can helpl me with this and thanks a lot!

Sounds like The Island of Doctor Moreau - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Island_of_dr._moreau)

There's a few versions of the movie

Island of Lost Souls (1932) (http://www.imdb.com/title/tt0024188/)

The Island of Dr. Moreau (1977) (http://www.imdb.com/title/tt0076210/)

The Island of Dr. Moreau (1996) (http://www.imdb.com/title/tt0116654/)

Your description reminds me of a film made in Spain.

Dagon (2001)
Aka Dagon: Sect of the Sea
Aka H.P. Lovecraft's Dagon
Aka The Lost Island
IMDb synopsis:
Based on a short story by H.P. Lovecraft, the undisputed master of the macabre, "Dagon" tells the story of Paul Marsh, a young man who discovers that the truth will not set him free. Instead, it condemns him to a waking nightmare of unrelenting horror. A boating accident off the coast of Spain sends Paul and his girlfriend, Barbara, to the decrepit fishing village of Imboca looking for help. As night falls, people start to disappear, and things not quite human start to appear. Paul finds himself pursued by the entire town. Running for his life, he uncovers Imboca's dark secret: They pray to Dagon, a monstrous god of the sea. Dagon's unholy offspring are freakish half-human creatures on the loose in Imboca. The most horrific revelation is yet to come.

Dagon (2001) - IMDb (http://www.imdb.com/title/tt0264508/?ref_=fn_al_tt_1)

Here's Part 1 on YouTube:
Dagon part 1/7 - YouTube (http://www.youtube.com/watch?v=TM5mzTjBPeY)

However, the couple do not escape. I think his fiancée is killed, and he finds that he belongs there.

EDIT: It could be another of the H.P. Lovecraft-based movies, too.