There are artificial reefs in Florida Keys National Marine Sanctuary

The term “artificial reef” covers a wide variety of human-made materials deliberately placed on the ocean floor in order to attract marine life and also for recreational purposes such as diving or fishing.
 
In general, artificial reef development is prohibited in national marine sanctuaries due to regulations that prohibit placing items on the sea bed or depositing materials. Currently, Florida Keys National Marine Sanctuary is the only national marine sanctuary to have approved artificial reefs within its boundaries.

The Florida Fish and Wildlife Conservation Commission runs one of the most active artificial reef programs along the Gulf and Atlantic coasts. Local county governments in Florida hold most of the permits for artificial reefs. There are more than 300 active artificial reef permits along the Florida coast, approximately 61 of which are located in sanctuary waters. The vast majority of these artificial reefs were deployed in waters of the Florida Keys prior to Sanctuary designation in 1990. 

Artificial reefs placed within Florida Keys National Marine Sanctuary were only deployed after an extensive evaluation and permitting process to ensure that their placement on the seafloor would not be detrimental to sanctuary resources and that the proposed benefits of the artificial reef were likely to be achieved.