Holocene marine ostracod species from Belize define four major biofacies. The Chetumal Bay biofacies, which extends southward along the mainland coast from Chetumal Bay to Belize City, is typified by low, variable salinities and water shallower than 20 ft (6.1 m).

The southern nearshore biofacies is restricted to a narrow strip along the coast south of Belize City. The faunal difference between the first two biofacies probably is controlled by differences in water chemistry of the influent streams; the rivers of northern Belize drain a low, flat-lying carbonate terrain, whereas the streams of southern Belize flow across the igneous and metamorphic rocks of the Maya Mountains.

The main-lagoon biofacies is characterized by a depth range from 20 to over 200 ft (6.1-61 m), normal-marine salinity, and a very fine-grained, commonly soupy substrate. This biofacies extends southward from the Chetumal Bay biofacies and is bounded by the southern nearshore biofacies on the west and by the carbonate-platform biofacies on the east.

The carbonate-platform biofacies faces the Caribbean Sea and is characterized by depths shallower than 30 ft (9.1 m) and water of normal-marine salinity, which supports abundant carbonate-secreting organisms, including reef-building corals. All biofacies, with the exception of the southern nearshore, may be further divided on the basis of their ostracod faunas.

The 105 species examined in this study include 4 new genera, 32 new species, and 1 new subspecies. Of the entire fauna, 29 species have been found as fossils, some dating back to the Eocene. Knowledge of the Holocene distribution of such long-ranging species offers a powerful tool for the paleoecologic interpretation of past sedimentary environments. At the generic level, assemblages from the various biofacies exhibit close similarity to ostracod associations found in Tertiary sedimentary formations of the Caribbean area.