The Littler books are good, there's the larger one for the Caribbean that's excellent(90-100$ or so) Caribbean Reef Plants, then there's a South Pacific Reef plants version (50$ etc).
Please note: what is found in nature does not imply that's what's best for horticulture(that's what we do). Many hobbyists make that assumption.
I do a 3 day Macro algae collection and ID class each Summer in the Florida Keys. I use the Littler book and some old stuff from way back, all drawings and looking at salient features.
It would be nice to do an on line key that folks could reference without that much jargon, they did a similar thing for the FW plants.
Regards,
Tom Barr