If you're going salt water fly fishing in a tropical climate for the first time it's easy to become over whelmed with the amount of gear that is out designed especially for doing so. While much of your equipment will suffice with proper care the one item used in tropical salt water fly fishing that can't be universal with your freshwater gear is your fly line. Salt water lines that are designed for warm water applications are really different from cold water lines. While many different tapers are available, similar to fresh water lines, it's the coating that makes all the difference. You are buying the line for temperature, not water type.
The harder coating on salt water fly lines will prevent them from getting limp and sticky under the tropical sun.
Lines for salt water have a much stiffer coating covering their core, while freshwater lines will wilt and be sloppy and sticky in the heat, salt water lines will continue to cast well and deliver your fly to its' target. You will also find that salt water lines of the same weight will be thinner than freshwater lines.
There are many choices out there for salt water lines these days.
This is because salt water is denser than freshwater so lines are more buoyant in salt water. There are many specialized saltwater fly lines on the market these days, with tapers designed for Bonefish through Billfish and everything in between but the beginner can't really go wrong with a "general purpose" salt water line.