Mate, pumps are generally used to transfer water from one place to another. If you have to desalinate, you'd probably need an industrial filter to do so instead.
You could try Waterco's desalination system, which is from Australia. They've listed themselves in the Australian Stock Exchange by...
When you're dealing with the sea, you'll need a specialised pump grading in titanium for sure. It'll offer the protective measure needed for the long-haul use.
Even if you're planning to draw in water, or in your case, nearby water from the marine ecosystem, I'd reckon to use the pump in...