Foraminifera live in the following environments in the Florida Keys area: Florida Bay, water 0-10 feet deep; the back-reef, water mostly 15-30 feet deep but ranging from 0 to 40 feet deep; the reef, locally awash at low tide but extending seaward to a depth of about 60 feet; and the fore-reef, water deeper than 60 feet. The boundaries between the back-reef and the reef and between the reef and the fore-reef environments are transitional.

The Florida Bay environment is characterized by great variations in the abundance of the Miliolidae, Peneroplidae, Nonionidae, and Rotaliidae, and by the absence of the Amphisteginidae, Textulariidae, Lagenidae, and Buliminidae. Variations in the Florida Bay fauna suggest sorting. The Amphisteginidae and Buliminidae represent families present in the back-reef environment which are not found in Florida Bay. The Peneroplidae and Amphisteginidae are most abundant and the Nonionidae are least abundant on the outer reef patches. The fore-reef environment is characterized by the appearance of the Cassidulinidae and the rise of the Anomalinidae to a position of minor abundance. Angulogerina, Bulimina, Uvigerina, and Reusella do not occur at depths much shallower than 150 feet.

These environments may be recognized and differentiated by noting the relative abundance of individuals belonging to the various families without regard to the species or genera involved.