Zoogeography of recent cytheracean ostracodes in the bays of Texas

The bays of the Texas coast consist of a series of lagoons, impounded behind an almost continuous barrier bar, and estuaries that occupy drowned Pleistocene river valleys. The ostracodes that inhabit these bays are euryhaline and eurythermal species adapted to a brackish water environment. The collections of Recent cytheracean ostracodes in this study are from 129 sediment samples taken from ten bays that span the length of the Texas coast. Forty-one species of cytheracean brackish water ostracodes, representing 20 genera, were recognized. Two genera. Perissocytheridea and Cytherura, contain 13 species and comprise 46% of the total ostracode population. A total of 32,189 ostracode specimens were recovered. Five species are new: Cytherura maddocksae, Cytherura mustangensis, Cytherura valentini, Magacythere texana, and Cytheretta swaini. Analysis of the collected faunas reveals that well-defined ostracode biofacies are developed in the bays. Distribution appears to be controlled primarily by salinity and substrate. The Texas coast is a uniform zoogeographic province without significant change of faunas along its length but increase in salinity of lower coast bays causes a shift up-bay of the principal biofacies. Species diversity increases from Sabine Pass to Corpus Christi Bay, but decreases in Laguna Madre. Within the bays species diversity is higher in the lagoons than in the estuaries or in the inlet zones. Highest species diversity was found in samples taken near oyster reefs. Comparison of the Texas fauna with adjacent areas shows that a high degree of homogeneity exists in the brackish-water faunas of the Gulf Coast from Mexico to Florida. A lower, but still appreciable degree of commonality (18 of 41 species) exists with the southern Atlantic coast, and very low commonality (4 of 41 species) exists between the Texas fauna and that of similar environments on the Pacific coast.