Officials for years have been cleaning up tire after tire from the ocean floor off Broward County — removing what was once meant to create a fish habitat but turned out to be an environmental mess. Hundreds of thousands of tires so far have been pulled out. And as more of them are taken away, the work grows more challenging. The cleanup was easy when the “diver just had to tie them up and send them up,” said Pat Quinn, a biologist for Broward County who is supervising the tire removal work.