The tropical, reef-bounded continental shelf of Belize encompasses a wide variety of marine and marginal-marine environments. The distribution patterns of foraminiferal assemblages in this area reflect this environmental diversity. The distribution is strongly influenced by the effect of both the seaward barrier and the adjacent landmass on the hydrography and sedimentation of the narrow shelf.

Nine foraminiferal assemblages are defined on the basis of taxonomic composition, faunal dominance, faunal diversity, and faunal density of total (living plus dead) foraminiferal populations.

A high-diversity miliolid-dominant assemblage occurs throughout the stenohaline, shallow-water areas of the barrier and outer platforms-areas characterized by calcium carbonate deposition and coral-reef growth. Areas of high turbulence on the windward edge of these platforms contain a unique Archaias-Asterigerina-dominant assemblage. A low-diversity miliolid-dominant assemblage is present in the northern shelf lagoon and Chetumal Bay, which are areas of variable salinity, shallow water, partially restricted circulation, and carbonate mud deposition. A unique low-diversity miliolid assemblage dominated by Archaias occurs in a part of Chetumal Bay behind a large carbonate island.

In the relatively deep southern shelf lagoon, a low-diversity Cribroelphidium-dominant assemblage occurs in two areas: (1) the landward part of the embayed Gulf of Honduras, an area influenced by high stream discharge, and (2) the lagoonal area that is adjacent to the barrier platform and is characterized by restricted circulation and mixed carbonate-terrigenous sedimentation. A high-diversity Cribroelphidium-dominant assemblage is present in deep lagoonal, stenohaline areas of uninhibited circulation. A Cribroelphidium-Quinqueloculina-dominant, mixed faunal assemblage marks the zone of influx of shoal-derived material into the lagoon. The deepest part of the continental shelf is the site of a Globocassidulina-dominant assemblage. The mainland coast of Belize is characterized by a Quinqueloculina-Cribroelphidium-dominant assemblage associated with nearshore quartzose sand and silt and a suite of marginal-marine assemblages including delta, marsh, and mainland-lagoon populations.

Data on living populations provide information concerning foraminiferal ecology but do not produce consistent, mappable faunal assemblages. Marked differences between the quantitative parameters of living and total populations in some areas are thought to result from recent shifting of environmental conditions and relict faunas, faunal displacement, seasonal and/or inadequate sampling of habitats, and unknown factors perhaps reflecting seasonal reproduction or differential rates of reproduction among species.