Radiolarian species composition, density, and diversity can be used to define the structure of the water column and circulation patterns of waters overlying the south Texas shelf. Radiolarian species that occur in the western North Atlantic, Caribbean, and Gulf of Mexico are also found in the south Texas shelf waters. The radiolarian assemblage from the western North Atlantic has the greatest density and diversity. Radiolarian densities and diversities are lower in the Caribbean and Gulf of Mexico, and are lowest in the waters over the shelf. Radiolarian densities and diversities on the shelf reflect incursions of open ocean waters at varying depths. Certain

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radiolarian assemblages and their position on the shelf, as well as radiolarian density and diversity can be used to identify winter, spring, and fall physical oceanographic conditions on the south Texas shelf. Radiolarians can also be used as indicators of physical oceanographic conditions in studies of ancient shelves.

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