There are many species of algae which thrive in salt water. In fact one set of them, blue green algae, might have advantages. These can survive in a higher saline environment, so a tank could be created which could not be contaminated by other species. However a highly saline environment is also highly corrosive, and so expenses would rise.
Salt water is pretty mild compared with many petroleums. It would be an odd complaint that it is too corrosive to deal with, and perhaps algae farms could be accommodated out in the ocean itself. The resulting bioharvest would still need to have salt flushed out of it, of course.