Today, following decades of human and natural impacts, this coral ledge topped by a lighthouse and fringed with rubble and sea grass still delights scientists and divers with its rich species diversity.

Islamorada underwater photographers Carlos and Allison Estape – volunteers with the nonprofit Reef Environmental Education Foundation (REEF) – recently embarked on their own fish count at Alligator Reef, a no-take zone ever since the 1997 implementation of the Florida Keys National Marine Sanctuary management plan. The couple is up to a little more than 100 species on a single dive, with the photographs to prove it. Lad Akins, longtime operations director for REEF, said the Upper Keys sanctuary preservation area is among only a few other known locations in the tropical Western Atlantic with a one-dive, 100-plus fish species count. Chief among them is the tiny island of Bonaire in the southern Caribbean.