I have the Reef Set by Humann and DeLoach. It is a 3 volume set. One volume for fish, another for corals and the third for "creatures" which means marine invertebrates. It covers almost anything you are going to see in the Caribbean. It is good at noting the "key" characters of the various organisms. This set is often on reference at most dive resorts and dive operators. The thing with field guides is the more the merrier. Different guides show different things. Some guides show the immatures which can often look quite different than the adults. The less ambitious guides will cover the more common creatures which make up about 95% of what you are going to see. Being able to ID the common stuff gives you a leg up in that when you see something that is not in the guide, you KNOW it is unusual. Also, if you have a camera, even a rather poor photo is good for using to ID the creature later.