Thanks to Rick and PZ, here's a task I can't resist, name a horror movie with an ocean theme.
The Lost Continent, after watching this you'll never again go on a marginal ship into dangerous waters with a cast of sketchy characters (wait a minute, that's oceanography!). Weird, not just horrific.
Classic, but too easy--Jaws, a movie that made me scared to swim in a lake!
Modern and obvious--Pirates of the Caribbean series, great effects and villian (kraken!)
Awesome, would have been my choice, but it's not quite ocean--Creature from the Black Lagoon, with a truly outrageous "synchronized swimming" scene where the creature swims beneath the babe.
This comes from the hallo-meme started by Rick at Malaria, Bedbugs, Sea Lice, and Sunsets, by way of Pharyngula.
Now it's my job to tag some others (sorry all, they made me do it):
Shiftingbaselines (this is a job for Randy Olson)